physicochemical studies of transition metal chelates · of macrocydic ligands and their transition...

PHYSICOCHEMICAL STUDIES OF TRANSITION METAL CHELATES

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T H E S I S SUBMtTTEO FOR THE AWARD OF THE DEGREE OF

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CHEMISTRY

BY

FOUZIA RAF A T

rii^ THESIS DEPARTMENT OF CHEMISTRY

ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA)

2004

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ABSTRACT

This thesis deals with the physicochemical studies of metal chelates

with multidentate ligands. The synthesis and characterization of a number

of macrocydic ligands and their transition metal complexes has been

described. The mode of bonding of the central metal ion to the ligand has

been studied by elemental analyses, IR, electronic, EPR and ^H NMR

spectra, TGA, magnetic moments and conductivity measurements.

The introductory chapter gives a brief account of coordination

compounds described in the literature. It also describes the aims and

objectives of the present work embodied in this thesis.

Second chapter describes the synthesis of two isomers of

[Cu(dien)Cl2] of two different colours (blue and yellow), where

dien = diethylenetriamine. They have been synthesized by a slight

variation in the procedure. Both complexes turn blue in aqueous, ethanolic

and DMSO solutions and attain a stable geometry. The blue isomer is

thermally more stable than the yellow one. Both of them have identical

spectra and molar absorption coefficient values in solution.

The second part of this chapter deals with the syntheses and

characterization of novel type of bimetallic salts obtained by transfer of

halide ions from one metal ion to another metal ion resulting in the

formation of a bigger anion stabilized by a copper(ll) complex cation. The

studies of these bimetallic salts was undertaken to explore the interaction

between two metal ions and halide ion transfer from one metal to another.

In chapter III, four new macrocycles containing pendant arm have

been prepared by treating 4-aminoantipyrine with (a) ethylenediamine and

(b) propanediamine. The products were further reacted with benzoylacetic

acid to yield the free macrocycles (L ) and (L'*) respectively. In the same

way, the free macrocycles (L ) and (L ) were isolated by treating 4-

aminoantipyrine, acetylacetone with (a) 1,6-diaminohexane and (b) 1,3-

diaminopropane. In order to investigate the coordination behaviour of

these ligands, their complexes with transition metal ions were synthesized.

Spectroscopic studies suggested that carboxyl and acetic acid pendant

groups do not take part in coordination. For all divalent and trivalent metal

complexes an octahedral geometry has been suggested. In the case of

trivalent metal ions the two chlorines appear to be covalently bonded while

the third one is present outside the coordination sphere.

Chapter IV (A) in this thesis describes Schiff bases derived from the

condensation of isatin with (a) ethylenediamine (L ) and (b)

diethylenetriamine (L^). The complexation of these ligands with divalent

and trivalent metal ions have been investigated. L acts as a neutral

tetradentate ligand coordinating with its two carbonyl oxygen atoms and

two azomethine nitrogen atoms while L acts as a pentadentate ligand.

3

Chapter IV (B) includes the syntheses and characterization of two

tetraaza Schiff base • macrocycle derived from the reaction of

triethylenetetramine with benzil and acetylacetone. Their transition metal

complexes have been synthesized and characterized by various

physicochemical methods.

Heterotrinuclear complexes of the type [Cu(ppn)2Cl2{Ti(Cp)2}2] and

[Cu(en)2(N03)2{Tj(Cp)2}2] have been synthesized by the reaction of

[Cu(ppn-H2)2]Cl2 and [Cu(en-H2)2]Cl2 with (Cp)2TiCl2 (where ppn-H2 = 1,3-

diaminopropane, en-H2 = 1,2-diaminoethane and Cp = cyclopentadienyl

group). The studies presented in chapter V focus on the synthetic scope of

the use of (Cp)2TiCl2 as a base. Upon binding of (Cp)2TiCl2 to the

mononuclear Cu(ll) complexes, there is a change in the geometry of the

Cu(ll) ion. EPR spectra show a change in the character of the ground state

of the Cu " ion as they move from mononuclear to trinuclear species

indicating distortion due to the attachment of CI".

In chapter VI, mixed ligand complexes of the type [M(dtc)2(bpy)] and

[M(dtc)2(phen)] (where M = Mn(ll), Co(ll), Ni(ll), Cu(ll) and Zn(ll), dtc =

N,N'-diethyldithiocarbamate, bpy = 2,2'-bipyridyl and phen = 1,10-

phenanthroline) were synthesized by the replacement of two chloride ions

in [M(bpy)Cl2] and [M(phen)Cl2] by diethyldithiocarbamate. They are further

characterized with the help of spectroscopic studies.

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PHYSICOCHEMICAL STUDIES OF TRANSITION METAL CHELATES

T H E S I S SUBMITTED FOR THE AWARD OF THE DEGREE OF

Bottor of $l|ilo!SQplip IN

CHEMISTRY

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BY

FQUZIA RAF A T

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DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

2004

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prof. K. 5. SCddCqO E-mail:[email protected] DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY ALIGARH-202 002(INDIA)

Date

Certvfixxcte/

Certified that the work embodied in this thesis entitled

"Physicochemical Studies of Transition Metal Chelates" is the result of

original research carried out by Fouzia Rafat under my supervision and is

suitable for submission for the award of the Ph.D. degree in Chemistry of

Aligarh Muslim University, Aligarh. ' C/^,

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Prof. K. S. Siddiq

mailto:[email protected]

AC10<IO\i)L€VGmENT

The/ accomplCihme'Vit of thX4^ endea^/our would/ not hove/ heev\/ fka&Oyle/ wCthotAt the/ wCd of AhnCghty Allah/. I very hu^mhly thcuxh AUdh cuxd/ pray to- hivw for farther HACce^ry (AvlCfe/.

I eicpren' my âtefulne^j cordially OAxd/ reli{,hCA\gly to-my nxperviior Prof. K. 5. SCddlqC/, Vepartmerxt of Chemlityy, AHârh Mu&lim/ UnCên^, Alig^nrh (India/) for hiy lAVi/aluahle/ aniduotA^ ûlda^vce/. HCy peni&t^B/nt diligence/ a/nd/ pen&i/erance/ wCth/ prompt reiponire/ wa^ courteou^^ a^xd/ iympathetCo txnvardy me/ throt^ghout the/ tenure/ of thi^ re4iearchprogram^yie/.

The/ Chalrmuw, Vepartme^^t of Che^mlatry, iAf êal^jy a<:kno\uledged/for pro^/Cdlng^ necoAary rcicarch/facility.

Hy yvncere/ gratilud/e/ and/ thanky go- to- Prof. J. Ca^cCbo-, Vepartment de/ Qulmlca/, UnOênltat Autonoryia/ d/e/"Barcelona/, Spalw and/Prof Y. Chehuxle/, Vepartment of ChemC&tyy, AddC&'Ahaha/linOi/erittyy Ethiopia/for their help i¥\/ mxlklng/ the/ quantvbatOife/ and/ cfuolCtctttve/ anaJyêy of the/ contpound/y poîihle/.

I a/m/ graijeJfvl/ to- the/ CoiAncd of Scientific and/ lndAA4trialf Keiiearch/ (CSIK), Wcw VeUU/ for aMjardCng- me/ Senior Ke&earchfeUowihip (SUf).

I am/ graljeJfvl/ to- Prof. K. J. Singh/, Prof. M. Mu4lxfiq and/ Vr. LutftARah/ for their valuable/ crOticiirm/, comtructi^/e/ dlica&iuyn/ and/ ivwportvmt yu^ggeatiorw.

I wiih/ to- e^cprcifi' my gratCtud/e/ to- my friend/ Kifat Tahaûryv for her encourage^nent and/ moral/ support. I aUo- e^re^y my hearty thanky to- all/ my coUeague^ for their con!itructO\/e/help froywtVme/to-tvme/.

I cxpray my sincere/ gratXtude/ to- my parenty, my hrothery and/ my sdyteryfor their comtant encourage4nent, QjyifiMXM\ce/ and/ affection/ which/ enabled/ me/ to- reach/ thiy ytage/ofmy life/and/to-convpl&t^ thiy worh.

(fow^fia/ Uafat)

Dedccate^/

I'D-My

List of Publications

1. Novel N4 Macrocycles and Their Transition Metal Chelates. K. S. Siddiqi, N. Nishat and Fouzia Rafat, Synth, and React. Inorg. Met.-Org. Chem., 2003, 33, 1835 -1855.

2. Preparation of the Two Isonners of [Cu(dien)Cl2]. K. S. Siddiqi, Fouzia Rafat and S. H. Kar, Synth, and React. Inorg. Met.-Org. Chem., 2004, 34, 93 - 99.

3. Synthesis and Characterization of Trinuclear Complexes Containing Cu(ll) and Ti(IV). Fouzia Rafat, K. S. Siddiqi and Lutfullah, Synth, and React. Inorg. Met.-Org. Chem., 2003, 34, 763 -774.

4. An Anionic Moiety, MCU ' (M = copper, zinc, cadmium and mercury) Stabilized by Bis(diethylenetriamine)copper(ll) Cation. K. S. Siddiqi, Fouzia Rafat, M. Y. Siddiqi, Lutfullah and Yonas Chebude, Polish J. Chem., 2004, 78, xxx -xxx.

5. Synthesis and Characterization of Complexes of Isatin Schiff bases. K. S. Siddiqi, Fouzia rafat and M. Y. Siddiqi, Polish J. Chem.,

(Accepted).

6. Synthesis and Physicochemlcal Properties of Schiff Base Macrocyclic Ligands and Their Transition Metal Chelates. K. S. Siddiqi, Fouzia Rafat and N. Nishat, J. Chinese Chem. Soc, (Communicated).

ABSTRACT

ABSTRACT

This thesis deals with the physicochemical studies of metal chelates

with multidentate ligands. The synthesis and characterization of a number

of macrocyclic ligands and their transition metal complexes has been

described. The mode of bonding of the central metal ion to the ligand has

been studied by elemental analyses, IR, electronic, EPR and ^H NMR

spectra, TGA, magnetic moments and conductivity measurements.

The introductory chapter gives a brief account of coordination

compounds described in the literature. It also describes the aims and

objectives of the present work embodied in this thesis.

Second chapter describes the synthesis of two isomers of

[Cu(dien)Cl2] of two different colours (blue and yellow), where

dien = diethylenetriamine. They have been synthesized by a slight

variation in the procedure. Both complexes turn blue in aqueous, ethanolic

and DMSO solutions and attain a stable geometry. The blue isomer is

thermally more stable than the yellow one. Both of them have identical

spectra and molar absorption coefficient values in solution.

The second part of this chapter deals with the syntheses and

characterization of novel type of bimetallic salts obtained by transfer of

halide ions from one metal ion to another metal ion resulting in the

formation of a bigger anion stabilized by a copper(ll) complex cation. The

studies of these bimetallic salts was undertaken to explore the interaction

between two metal ions and halide ion transfer from one metal to another.

In chapter III, four new macrocycles containing pendant arm have

been prepared by treating 4-aminoantipyrine with (a) ethylenediamine and

(b) propanediamine. The products were further reacted with benzoylacetic

acid to yield the free macrocycles (L ) and (L'*) respectively. In the same

way, the free macrocycles (L ) and (L ) were isolated by treating 4-

aminoantipyrine, acetylacetone with (a) 1,6-diaminohexane and (b) 1,3-

diaminopropane. In order to investigate the coordination behaviour of

these ligands, their complexes with transition metal ions were synthesized.

Spectroscopic studies suggested that carboxyl and acetic acid pendant

groups do not take part in coordination. For all divalent and trivalent metal

complexes an octahedral geometry has been suggested. In the case of

trivalent metal ions the two chlorines appear to be covalently bonded while

the third one is present outside the coordination sphere.

Chapter IV (A) in this thesis describes Schiff bases derived from the

condensation of isatin with (a) ethylenediamine (L ) and (b)

diethylenetriamine (L^). The complexation of these ligands with divalent

and trivalent metal ions have been investigated. L acts as a neutral

tetradentate ligand coordinating with its two carbonyl oxygen atoms and

two azomethine nitrogen atoms while L acts as a pentadentate ligand.

Chapter IV (B) includes the syntheses and characterization of two

tetraaza Schlff base macrocycle derived from the reaction of

triethylenetetramine with benzil and acetylacetone. Their transition metal

complexes have been synthesized and characterized by various

physicochemical methods.

Heterotrinuclear complexes of the type [Cu(ppn)2Cl2{Ti(Cp)2}2] and

[Cu(en)2(N03)2{Ti(Cp)2}2] have been synthesized by the reaction of

[Cu(ppn-H2)2]Cl2 and [Cu(en-H2)2]Cl2 with (Cp)2TiCl2 (where ppn-H2 = 1,3-

diaminopropane, en-H2 = 1,2-diaminoethane and Cp = cyclopentadienyl

group). The studies presented in chapter V focus on the synthetic scope of

the use of (Cp)2TiCl2 as a base. Upon binding of (Cp)2TiCl2 to the

mononuclear Cu(ll) complexes, there is a change in the geometry of the

Cu(ll) ion. EPR spectra show a change in the character of the ground state

of the Cu^* ion as they move from mononuclear to trinuclear species

indicating distortion due to the attachment of CI".

In chapter VI, mixed ligand complexes of the type [M(dtc)2(bpy)] and


N,N'-diethyldithiocarbamate, bpy = 2,2'-bipyridyl and phen = 1,10-

phenanthroline) were synthesized by the replacement of two chloride ions

in [M(bpy)Cl2] and [M(phen)Cl2] by diethyldithiocarbamate. They are further

characterized with the help of spectroscopic studies.

CONTENTS

Title Page#

Chapter I Introduction 1

Chapter II 20

(A) Preparation of the two isomers of [Cu(clien)Cl2] (Blue isomer and yellow isomer)

(B) An MCI/" moiety (M = Cu(ll), Zn(ll), Cd(ll) and Hg(ll) stabilized by bis(diethylenetriamine)copper(ll) cation

Chapter III Novel N4 macrocycles and their transition metal 43 chelates

Chapter IV 69

(A) Synthesis and characterization of complexes of Mn(ll), Fe(lll), Co(ll), Ni(ll), Cu(ll) and Zn(ll) with Schiff bases derived from isatin and polyamines

(B) Synthesis and physicochemical properties of Schiff base macrocyclic ligands and their transition metal chelates

Chapter V Synthesis and characterization of trinuclear 104 complexes containing Cu(ll) and Ti(IV)

Chapter VI Synthesis and characterization of metal complexes 120 containing dithiocarbamate and polypyridine

CHAPTER I

INTRODUCTION

INTRODUCTION

The condensation of primary amines with carbonyl compounds was

first reported by Schiff and since then the condensation products are

referred to as Schiff bases.

The coordination complexes of a wide variety of Schiff-base ligands

have been extensively studied and reviewed. "^ Those with ligands

containing sp^- hybridized nitrogen atoms, particularly when acting as bi- or

poly-dentate ligands, give very stable coordination compounds. Of them,

diimine ligands containing the 1,4-diaza-1,3-butadiene skeleton (N=CC=N)

with two conjugated C=N iminic bonds, have attracted most interest.

Closely related to those are the di-Schiff base ligands containing two N sp^

donor atoms as part of a non conjugated ( =NCCN=) system. Those

derived from salicylaldehyde and diamines (N,N'-bis(salicylidene)

ethylenediamine) are recognized chelating agents, giving complexes of

almost all metal ions, in which complex formation is determined by metal-

nitrogen and metal-oxygen bonds.°

Mikuriya^ and coworkers made a detailed study of crystal structure

and magnetic properties of alkoxobridged copper(ll) complexes with Schiff

base ligand (Fig. 1). Recently, Ceder et al. ° have synthesized the

organometallic complexes containing di-Schiff bases acting as neutral

bidentate (NiX(R)NN) ligands.

Fig. 1

Haikarainen et al. ^ have synthesized and characterized new bullcy

salen type ligands (Fig. 2) and their complexes with first row transition

metals, Mn, Fe, Co, Ni and Cu.

ClPhjP .Q^-\f-. e PhjCl

Fig. 2

The metal derivative of these ligands have drawn substantial

attention from the researchers for their biological activities. ' ^ Many Schiff

base ligands have also been derived from sulpha drugs^^^^ and their

coordination chemistry studied."" " ^ The molecules of life such as amino

acids have been exploited for the synthesis of Schiff base ligands and their

transition metal complexes 22-31 Schiff-base metal complexes are

considered to be a new kind of potential anticancer and antivirus

reagent. " ^ However, the antitumor activities of these compounds are

difficult to measure because of their low solubility in both aqueous and

organic media. Moreover, since they are administered as suspensions, the

particle size may affect their activities. Recently, Xiao and Zhang^ have

successfully synthesized a novel water soluble polymeric Schiff-base

nickel(ll) complex and studied its interaction with Calf thymus DNA.

Chemistry of isatin (indole-2,3-dione) dates back well to the 19*

century because of its relationship with the pigment indigo. Isatin and

some of its relatively simple derivatives are pharmacologically relevant e.g.

isatin "inhibits natriuretic peptide-induced hyperthermia in rats" ^ and some

of its semicarbazones show anticonvulsive activity.^^

Isatins have a major importance in organic chemistry as they can be

used for the synthesis of a variety of heterocyclic compounds, such as

indoles and quinolines. ^ The synthetic versatility of these compounds has

led to their extensive use in the pharmaceutical industry since they can be

used as raw materials for drug synthesis.

In nature, isatin and substituted isatins are found in plants,^* for

instance the melosatin alkaloids (methoxy phenylpentyl isatins),^^ and also

in humans as they are metabolic derivatives of adrenalin.'*"

Several Schiff bases and hydrazones of substituted isatins were

prepared by reacting isatin and aromatic primary amines/hydrazines.'*^"^^

Recently, a new series of the corresponding Schiff base was synthesized

by reacting isatin with formaldehyde and diphenyl amine.'*^

We also, have synthesized Schiff bases from the condensation of

isatin with (a) ethylenediamine (L ) and diethylenetriamine (L^). The

complexation of divalent and trivalent metal ions have further been

investigated.

Macrocyclic chemistry is now a well established interdisciplinary field

bridging organic and inorganic coordination chemistry. The multidentate

macrocycles give rise to unique, rather cryptic geometries'*^^ on

complexation with metal ion.

The recognition of a metal ion by a macrocyclic ligand and

modification of the properties of the resulting complex is controlled to a

large extent by a match between the size of the metal ion and the cavity

provided by the macrocycle. The chemistry of macrocyclic compounds is,

therefore, considered as an important field of research due to the

encapsulation capability of a metal ion within a ligating framework.

The macrocyclic ligand (Fig. 3) has been prepared by metal-

templated, Schiff-base condensation of 2,6-dicarbonylated pyridine and

1,2-diaminocyclohexane.'*^ Their efficiency as catalysts for double-

stranded DNA hydrolysis and NMR imaging have also been reported by

Bligh and coworkers.'*^ Recently Tsubomura et al.'*° have reported the

crystal structure of metal complexes of that ligand. The framework of the

macrocycle is so flexible that the complexes can adopt a variety of

conformations. Most complexes of such ligands adopt a folded butterfly

conformation. Ayala et al."* and some other workers^°' ^ have pointed out

that there is a correlation between the size of the metal ion encapsulated

and the cavity formed by the macrocycle. Generally, the complexes

containing large metal ions have a tendency to show planar conformation.

On the other hand, the ones containing small metal ions show folded

conformation.'*^

Fig. 3

Macrocydic ligands can be synthesized either by metathesis or via

template synthetic routes. The latter is preferred because of the

conformational requirements of the reacting species. Hori et al.^^ have

prepared the macrocydic ligand by template method in the following way

(a) the preparation of an acyclic proligand possessing N(amine)202 and

0(formyl)202 metal-binding sites and (b) the 1:1 condensation of the

proligand with a diamine by a template reaction Fig. 4. Template method

gives high yielding and selective routes to new ligand and their complexes.

X

HjN-L'-NHj

Template cyclization

Fig. 4

The coordination chemistry of transition metals in (+11) oxidation

state (M = Cu(ll), Ni(ll) or Pt(ll)) with macrocyclic tetraamine N4 has

extensively been studied.^'^^ Especially, the 14-membered tetraamine

macrocycles incorporate metal ions into their N4 cavities to form kinetlcally

and thermodynamically stable complexes. ^ For example, the 1,4,8,11-

tetraazacyclotetradecane-5,7-dione ligand (dioxocyclam) possess two

amide and two secondary amine groups.^ (Fig. 5)

In the present work, the synthesis and characterization of two

tetraaza 12 and 13 membered Schiff base macrocycle derived from the

reaction of triethylenetetraamine with benzil (L ) and acetylacetone (L°)

has been described. Their complexes with transition metal have been

synthesized and characterized by various physicochemical methods.

Ox .0

^ N-

H

—N N ^ H

Fig. 5

The coordination properties of macrocycles bearing pendant groups

have attracted great deal of attention. ®"^^ The crystal and molecular

structure of [3-(4-pyridiniumcarbonyl)1,3,5,8,12-pentaazacyclotetradecane]

nickel(ll) was described^^ in which pyridine acts as a pendant group.

Metallocyclam subunit has been appended to pyridine through metal

template procedure which involves the condensation of amides of 3 and 4-

pyridine carboxylic acid with formaldehyde and nickel(ll) complex with the

open chain tetraamine. These metallocyclam units act as building blocks of

supramolecular system.

Recently, a new pyridine armed aza crown ether was prepared with

the reductive amination of monoaza-15 crown-5 with sodium

borohydrideacetate in 1,2-dichloroethane.^ (Fig. 6)

Indeed macrocyclic systems incorporating appended 2-pyridyl

methyl arms have been documented to exhibit a wide variety of interesting

Fig. 6

and often novel metal coordination behaviour.®^

Recently Gou and coworkers^^ prepared four novel tetranuclear

copper(ll) complexes of 2:2 macrocyclic Schiff bases with functional

X

H2L' : X = CH3, Ar = Furanyl, H2L2: X = CI, Ar = Furanyl

HiL^: X = CI, AT = Phenyl HjL^ : X = CH3, Ar = Phenyl

Fig. 7

pendant arnns (H2L " ), by the condensation of sodium 2,6-diformyl-4-X-

phenolate (X = CI, CH3) with the reduced 1:1 Schiff base of diformyl-4-X-

phenolate (X = CI, CH3) with the reduced 1:1 Schiff base of 2,2',2"-

tris(amlnoethyl)amine (tren) and 2-formyl furan (or benzaldehyde) followed

by in situ transmetallation with copper(ll) perchlorate (Fig. 7).

Lindoy and Dong® have also synthesized a series of tetraaza N-

benzoylated cyclam derivative by treating benzyl bromide and cesium

carbonate to a stirred solution of 1,4,8-tris(tert-butoxy-carbonyl)-1,4,8,11-

tetraazacyclotetradecane in dry acetonitrile. Deprotonation by using 3M

HCI-MeOH results in the formation of cyclam derivative (Fig. 8).

n k" H

/ -N N—I

^

r^N N

1—N N—I

H "H

N N-

I—N N—' H

Fig. 8

In this thesis some new 13, 14 and 17 membered Schiff base

macrocycles ( L \ L , L^ and L'*) containing pendant groups and their

transition metal complexes have been synthesized with a view to studying

the nature of the complexes. The possibility of the binding of the pendant

group has also been explored. For this purpose, the 4-aminoantipyrine was

allowed to react with (a) ethylenedlamine and (b) propanediamine to form

Schiff base which was further allowed to react with benzoylacetic acid

resulting in the formation of N4 macrocycles (L ) and (L'*) respectively. In

the same way, the macrocycles (L ) and (L ) have been obtained from a

Schiff base derived from the condensation of 4-aminoantipyrine with

acetylacetone and its subsequent reaction with (a) 1,6-diaminohexane and

(b) 1,3-diaminopropane.

Chemistry of heterobimetallic complexes has assumed importance,

owing to their diverse application in homogeneous catalytic processes, in

enzyme model systems for metalloproteins, viz. superoxide dismutase,

oxidases, peptidases and magnetic exchange between the paramagnetic

centers. ^^^ Bioinorganic chemists have made considerable efforts to

study the active sites involving more than one metal center due to their

diversity in biology^ ' ^ e.g. dicopper sites in hemocyanin and tyrosinase,

diiron(lll) sites in ribonucleotide reductase and heterobimetallic sites of

iron(lll) and copper(ll) in respiratory cytochrome oxidase, which catalyses

10

the four electron reduction of dioxygen to water in the mitochondria of

eukaryotic cells.

Heterobinuclear complexes containing cyclopentadienyl rings have

attracted increasing interest in the chemistry of metal complexes/'*

Fig. 9.

In this thesis, the synthesis and characterization of heterotrinuclear

complexes of type [Cu(ppn)2Cl2{Ti(Cp)2}2] and [Cu(en)2(N03)2{Ti(Cp)2}2]

are reported, where ppn-H2 = 1,3-diaminopropane, en-H2 =

1,2-diaminoethane and Cp = cyclopentadienyl.

Dithiocarbamate is another class of versatile chelating ligands and

forms stable complexes which display interesting and often quite novel

properties. Much attention has been devoted to the study of

dialkyldithiocarbamates^^^^ and their respective complexes with a wide

variety of cations. They are also used as fungicides, pesticides,

vulcanization accelerators, floatation agents and high pressure

lubricants.'' Dithiocarbamates were chosen for two reasons: first, they

provide varying degree of charge to the overall complex. Second, they can

11

be easily prepared from the readily available secondary amines or amino

acid derivatives.

Dithiocarbamate ligands have generally been found to coordinate to

a transition metal ion as a bidentate^^^ or a monodentate ligand^°' ^

(A and B).

M ;x ; : r r ^NR /C NR, S' /

(A) (B)

The dithiocarbamate ions have been used widely in analyses of

many elements, because the ions form chelate complexes, which exhibit

high extractabilities into organic solvents, with many kinds of metal ions. ^

Recently, some bioactivities of the dithiocarbamate ions such as inhibition

of growth of cancer cells has made dithiocarbamate important in the field

of biology and medicine. Since these bioactivities significantly alter with

coexistence of heavy metal ion, a relationship between the metal

dithiocarbamate and the bioactivities has become significant.

Mixed ligand complexes of the type [M(dtc)2(bpy)] and


diethyldithiocarbamate, bpy = 2,2'-bipyridine and phen = 1,10-

phenanthroline) were synthesized by the replacement of two CI" ion in

[M(bpy)Cl2] and [M(phen)Cl2] by N,N'-diethyldithiocarbamate. Effort has

12

been made to explore whether diethyldithiocarbamate bonded to a metal

Ion is In bidentate or monodentate fashion. The complexes are further

characterized by elemental analyses , IR, electronic, EPR and ^H NMR

spectra, magnetic moments and conductivity measurements.

13

REFERENCES

1. S. Yamada, Coord. Chem. Rev., 1965,1, 415.

2. L. Sacconi, Coord. Chem. Rev., 1966,1, 126.

3. R. H. Holm, G. W. Everett Jr. and A. Chakravorty, Prog. Inorg. Chem., 1966, 7, 83.

4. R. H. Holm and M. J. O'Connor, Prog. Inorg. Chem., 1971,14, 241.

5. S. Yamada and A. Takeuchi, Coord. Chem. Rev., 1982, 43, 187.

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14

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15

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16

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17

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18

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19

CHAPTER II

(A) PREPARATION OF THE TWO ISOMERS OF

Cu(dien)Cl2

BLUE ISOMER

YELLOW ISOMER

PREPARATION OF THE TWO ISOMERS OF Cu(dien)Cl2

The diethylenetriamine (dien) is known to form two fused-five

membered rings with metal ions."* For most metal chelates, specially the

complexes of first row transition metals with polyamines, five membered

chelate rings are the most stable ones." Two concepts are generally

referred to explain the increased stability of chelate complexes as

compared to those with monodentate ligands

(i) The proximity of the other ligand atom(s) of the chelate once the

first metal ligand bond is formed.'* This is based on the

geometrical consideration and is rather qualitative.

(ii) The more positive entropy of the formation of the chelate

complex.

Diethylenetriamine (dien) may act as a tridentate ligand towards

transition metal ions and may coordinate with a bent or planar

conformation of the ligand molecule.® Stephens has reported that the

compound [Cu(dien)2](N03)2 has a tetragonally distorted octahedral

[Cu(dien)2f * unit with C2 symmetry and uncoordinated NO3' groups.^ The

five coordinate complexes of Cu(ll) and Ni(ll) with dien have been

reviewed extensively to their molecular structures'^ and the possible

source of electronic origin that may contribute to the observed structural

20

distortions.''""^^ The compounds [Cu(dien){N03)2] and [Cu(dien)(formiate)2]

were prepared by Nikolov^^ and Stephens ' in order to assess the possible

manifestations of the Jahn-Telier effect in multidentate Cu(ll) complexes. It

has been observed that the [Cu(dien)(formiate)2] complex is square

pyramidal while [Cu(dien)(N03)2] complex is either trigonal bipyramid with

the dien ligand in a meridional position or a square pyramid with an apical

oxygen atom of the nitrate group. The dien ligand shows little variation in

the [Cu(dien)f * and [Cu(dien)2] * units though it is somewhat more relaxed

in the second unit. The strain in the chelate rings is felt by inner ring

chelate or bite angles. It is observed that the strain is less in the mono-dien

compound than in the bis-dien compound.

The possibility of the formation of a series of compounds of Cu(ll)

with dien in 1:1 molar ratio having different colours and different

stereochemistry has not been explored. The synthesis of Cu(ll) complex

with dien was, therefore undertaken in order to examine if it yields more

than one complex of the same composition but different physical

properties. It is expected that the rigidity of the dien molecule would hinder

the free distortion of the complex subject only to the Jahn-Teller forces that

restrict the number of possible geometries.

Synthesis of blue isomer of [Cu(dien)Cl2]

To a solution of CuC^ 2H2O (10 mmol, 1.7 g) in methanol (15 mL),

diethylenetriamine (10 mmol, 1.0 g) in methanol (15 mL) was added. The

21

resulting blue mixture was left for three hours at room temperature when it

yielded a blue crystalline compound. It was filtered, washed with cold

methanol and dried over CaCl2 in vacuo. Yield, 1 g (44%).

Synthesis of yellow isomer of [Cu(dien)Cl2]

For the synthesis of yellow complex a 1:4 aqueous methanolic

solution (25 mL) of diethylenetriamine (10 mmol, 1.0 g) was added to the

methanolic (15 mL) solution of CUCI2 2H2O (10 mmol, 1.7 g). The pH of the

mixture was adjusted to 2 by the addition of 0.1 M HCI which was

monitored by pH meter.""* The resulting green mixture was evaporated to

dryness which yielded a yellow amorphous compound. It was filtered,

washed with an ice-cold 1:2 ethanol - methanol mixture and dried over

CaCl2 in vacuo. Yield, 0.78 g (33%).

RESULTS AND DISCUSSION

By varying the method of synthesis, diethylenetriamine (dien) yielded

a set of two complexes of different colours, blue and yellow, but with the

identical composition [Cu(dien)Cl2]

CuCl2-2H20 + dien

Mm Blue isomer

Aq. MeOH pH = 2

-*• Yellow isomer

22

Both complexes turn blue when dissolved in water, ethanol or DMSO

although in the solid state they are stable with sharp melting points. Both of

these could not be recrystallized because they give only a blue solution

which becomes sticky after standing for fifteen days. The change in colour

and other physical properties of the complexes are due to non-planarity of

the dien molecule. Although the changes are very small, they have a

considerable effect on the geometry of the complex. The electronic spectra

of both the complexes in solution are identical with a common peak around

600 nm. The molar absorbance coefficient (e) values range between

2.32-2.35 L mol'"" cm-\

Table I. Analytical Data, Melting Points and Physical Properties of the Isomers of [Cu(dien)Cl2]

Isomer

Yellow C4H,3Cl2CuN3

Blue C4H,3Cl2CuN3

M.p. (°C)

245

238

Yield (%)

33

44

Analysis, % C H

19.6 (20.0)

19.5 (20.0)

5.6 (5.5)

5.6 (5.5)

Found (Calcd.) N CI

16.5 (17.7)

16.5 (17.7)

29.8 (29.8)

29.7 (29.8)

Molar conductance

ohm'' cm^ mol' DMSO MeOH

51 156

50 152

It is noteworthy that a slight variation in the method of synthesis

makes a large difference in the colours and melting points of the

complexes. Analytical data and molar conductance of the complexes are

23

given in Table I. The complexes were dried at about 100 °C before

analyzing them.

As a consequence of a change in the orientation of the dien ring

there is a change in the position of the nitrogen atoms which causes a

change in the colour of the isomers. Also from the crystal and molecular

structure of blue [Cu(dien)(N03)2], it has been confirmed that the geometry

of Cu(ll) is square-pyramidal. ' ^

v_y Fig. 1. Possible geometrical variation in [Cu(dien)Cl2]

The molar conductance of 1.0 x 10' M solution of the complexes in

DMSO and MeOH measured at room temperature is intermediate between

1:1 and 1:2 electrolyte^^ (Table I). This is possibly due to stepwise

dissociation of the complex in solution where the equilibrium is largely

shifted towards the right although the solvent molecule may occupy the

place of chlorine to maintain the square planar geometry of the complex in

solution.

24

The dissociation can be shown as follows

[Cu(dien)Cl2] ^ [Cu(dien)Cir + Cr

[Cu(dien)Cir -> [Cu(dien)r + CI"

The electronic spectra of the isomers in DMSO are similar (Table II).

They show a common peak at 255 nm which moves slightly towards

262-267 nm on dilution (Log £ = 3.39). The lower-energy bands

(612-629 nm) are broad and weak and are assigned to T2g <— Eg

transition. The high energy band is most probably due to the dien

molecule. Since the two isomers turn blue in DMSO and MeOH, it is

believed that, in solution, both complexes achieve square-planar geometry.

Table II. Colour of the Solid, Solution, Absorption Bands and Log e of the isomers

Colour Colour X, Loge X, of the of (nm) (DMSO) (nm) solids solution (L mol"' cm"')

Loge (MeOH)

(L mol"' cm"')

Yellow Blue 255 3.39 612 2.32

Blue Blue 256 3.39 629 2.35

It is concluded that the change in orientation of [Cu(dien)Cl2] is due

to the non-planarity of the dien molecule. The IR spectrum of the free dien

molecule exhibits two bands in the range of 3360-3295 cm" which are

shifted to lower wave number after chelation. The bands at 3280-3150 cm"

9S

and 3230-3020 cm' are assigned to the primary and secondary amino

groups, respectively. It is evident that the dien molecule is coordinated in a

tridentate manner. A very strong band at 660-980 cm"'' has been observed

for both isomers. There are two more prominent bands at 1030-1055 and

1085-1180 cm'\ The IR spectrum of the yellow complex recorded in air

shows a band at 1180 cm' which does not change even after six weeks

while the blue complex shows a band at 1085 cm" which also does not

change within this time period. Both these complexes are highly stable so

long as they are kept as solids. These minor differences support the

existence of isomers of [Cu(dien)Cl2] probably due to a slight change in

Cu-N bond lengths (Fig. 1).

From the IR spectral study, it has been shown that Cu(ll) appears to

be five coordinate but the EPR study indicates that interaction occurs

between two copper atoms of different units . It is possible only through

chlorine bridging between two such moieties as shown below (Fig. 2).

HN-

H2 -N

-N H2

CI

"•V CI

H2 N-

N-

•NH

Fig. 2. The bridged structure of [Cu(dien)Cl2]2

26

The bridging structure between two Cu(ll) atoms does not alter the

geometry of the complex as suggested by EPR. For the yellow complex,

one broad signal is observed, possibly due to Cu(ll)-Cu(ll) dipolar

interactions. The flow of electrons from chlorine to metal and back (Fig. 2)

may produce a dipole on one metal which may interact with other Cu(ll) ion

of the opposite dipole. The value of g for the yellow complex is 2.11 Gauss.

For the blue complex, only one site of Cu(ll) with gj. and g|

components is observed. The dipolar interaction between Cu(ll>-Cu(ll)

does not obliterate the gx and g|| components. The value of the gi

component for this complex is 2.184 Gauss and the value of g| is 2.051

Gauss. It supports that 6^ may be the ground state as gi > g|| > 2.02.'' It

has been reported^^ that for an ionic environment gp > 2.3, while for a

covalent environment g|| < 2.3, indicating that the present complex exhibit

considerable covalent character. The g values are related by the

expression

which measures the exchange interaction between copper centers. If

G > 4, exchange interaction is negligible and if G < 4, considerable

exchange interaction occurs in the solid complexes. For the blue isomer

the axial symmetry parameter (G) lying at 0.277 indicates a considerable

exchange interaction.

27

CHAPTER II

(B) AN MCl4 ' MOIETY ( M = Cu(II), Zn(II), Cd(II) and

Hg(II) STABILIZED BY

BIS(DIETHYLENETRIAMINE)COPPER(II) CATION

[Cu(dien)2]lCuCl4l

[Cu(dien)2]lZnCl4]

[Cu(dien)2][CdCl4]

[Cu(dien)2]lHgCl4l

AN MCI/- MOIETY ( M = Cu(ll), Zn(ll), Cd(ll) and Hg(ll) STABILIZED BY

BIS(DIETHYLENETRiAMINE)COPPER(ll) CATION

Tetracoordinated complexes in which all ligands bonded to the

metallic core are halogen atoms are well established. Bailer and Busch

term such compounds as strictly halide complexes. ^ The synthesis and

stabilization of such complexes is a recent matter of concern. °' ^

Schrobilgen and coworkers have reported the synthesis and stabilization of

tetrachloroarsonium and tetrabromoarsonium cations using weakly

coordinating bulky anions as counteranions.^° It has been reported that

[AsCl4][As(OTeF5)6] is stable while [AsBr4][As(OTeF5)6] undergoes slow

decomposition at room temperature but is kinetically more stable than

AsFe' and AsF(OTeF5)5' salts, which rapidly decompose upon warming at

room temperature. It has also been reported that the As(OTeF5)6' anion is

more weakly coordinating towards AsCU" than AsFe". A family of cyano

bridged copper(ll) - copper(l) mixed valence polymer containing diamine

ligands of formula [Cu(pn)2][Cu2(CN)4] has been prepared with the aim of

analyzing how their architecture may be affected by the steric constraints

imposed by the diamine ligand. ^ It is, therefore, considered essential to

evaluate the phenomenon associated with the formation of tetrachloro

complex anions (MCU ") of copper, zinc, cadmium and mercury stabilized

by a transition metal complex such as bis(diethylenetriamine)copper(ll)

28

cation. Here the synthesis and characterization of novel bimetallic salts of

the type [Cu(dien)2][MCl4] are reported.

EXPERIMENTAL

Diethylenetriamine and hydrated metal chlorides (BDH) were used

as received. Elemental analyses were carried out with a Perkin Elmer,

Seriesll CHNS/0 analyzer 2400, USA. Chlorine was determined

gravimetrically as AgCI. IR spectra (4000-200 cm" ) were recorded on a

RXI FT-IR spectrometer as KBr discs. The conductivity measurements

were carried out with CM-82T Elico conductivity bridge in DMF. The

electronic spectra were recorded on a Cintra 5GBC spectrophotometer in

DMF. Magnetic susceptibility measurements were done with a 155 Allied

Research vibrating sample magnetometer at room temperature. EPR

spectra of copper complexes were recorded on a RE-2X Jeol EPR,

spectrometer fitted with 100 KHz field modulation. The TGA was

performed with a Perkin Elmer thermal analyzer. The experiment was done

in nitrogen atmosphere using calcinated AI2O3 as reference material. The

weight of the sample taken was 8 mg and the heating rate was 10°C min'\

Synthesis of [Cu(dien)2]Cl2

CuCb 2H2O (10 mmol, 1.7 g) dissolved in methanol (25 mL) was

added to a methanolic solution (15 mL) of diethylenetriamine

(20 mmol, 2.17 mL) at room temperature, which immediately yielded a blue

29

crystalline compound. Since the yield was increased by cooling, the

contents were cooled to about 5 "C for 1 h. It was then filtered, washed

with cold methanol and diethyl ether and dried over CaCIa under vacuo.

Yield, 2.4 g (71%).

Synthesis of [Cu(dien)2][CuCl4]

A methanolic solution of CUCI2 2H2O (10 mmol, 1.7 g) was added to

[Cu(dien)2]Cl2 (10 mmol, 3.4 g) dissolved in methanol (20 mL). The mixture

was stirred for five minutes which resulted in the precipitation of bright blue

complex. The precipitate was removed by filtration, washed with methanol,

diethyl ether and dried over CaCl2 under vacuo. Yield, 4.2 g (89%).

Synthesis of [Cu(dien)2][ZnCl4]

A methanolic solution of zinc chloride (10 mmol, 1.4 g) was added to

[Cu(dien)2]Cl2 (10 mmol, 3.4 g) dissolved in methanol (20 mL). The mixture

was stirred for five minutes which resulted in the precipitation of blue

coloured complex. The precipitate was removed by filtration, washed with

methanol, diethyl ether and dried over CaCl2 under vacuo. Yield, 3.7 g

(79%).

Synthesis of [Cu(dien)2][CdCl4]

A methanolic solution of CdCb 2H2O (10 mmol, 2.2 g) was added to

[Cu(dien)2]Cl2 (10 mmol, 3.4 g) dissolved In methanol (20 mL). The mixture

30

was stirred for five minutes which resulted in the precipitation of blue

coloured complex. The precipitate was removed by filtration, washed with

methanol, diethyl ether and dried over CaCl2 under vacuo. Yield, 3.5 g

(67%).

Synthesis of [Cu(dien)2][HgCl4]

A methanolic solution of mercuric chloride (10 mmol, 2.7 g) was

added to [Cu(dien)2]Cl2 (10 mmol, 3.4 g) dissolved in methanol (20 mL).

The mixture was stirred for five minutes which resulted in the precipitation

of light blue complex. The precipitate was removed by filtration, washed

with methanol, diethyl ether and dried over CaCb under vacuo. Yield, 3.8 g

(63%).


The reaction of cupric chloride with diethylenetriamine in methanol in

1:2 ratio yields bis(diethylenetriamine)copper(ll) dichloride. Further

reaction of this compound with dichlorides of Cu(ll), Zn(ll), Cd(ll) and Hg(ll)

gives stable ionic bimetallic complexes.

CUCI2 + 2dien ^ ^ ^ ^ Pu(dienyCl2 (1)

[Cu(dienyci2 ^ MCI2 ^ ^ ^ ^ [Cu(dieny [MCI4] (2)

where M = Cu(ll), Zn(ll), Cd(ll) or Hg(ll)

31

The elemental analyses (Table III) correspond to [Cu(dien)2][MCl4]

[( M = Cu(ll), Zn(ll), Cd(ll) and Hg(ll)]. Electrical conductivity of 10" M

solution of the bimetallic species in DMF (81-98 ohm' cm^mor"") fall in the

range of 1:1 electrolyte.^^ The quantitative estimation of chloride ion as

AgCI confirms the presence of four chloride in the bimetallic species. ^ It is

apparent that these complexes are formed by the chloride ion transfer from

bis(diethylenetriamine)copper(ll) dichloride to metal dichloride added,

resulting in formation of larger anions, MCl/' which are stabilized by the

bis(diethylenetriamine)copper(ll) cation. It has been found that the reaction

of [Cu(en)2]Cl2 with [M(PPh3)2Cl2] M = Ni(ll) or Co(ll) yielded

[Cu(en)2][NiCl4] and [Cu(en)2][CoCl4], respectively, (equation 3) with the

precipitation of triphenylphosphine which was separated by dissolution in

diethyl ether leaving behind [Cu(en)2][MCl4].

[Cu(en)2]CL, - [M(PPh3)2Cl2] ^ ^ ^ [Cu(en)2][MCU] (3) -2PPh3

where M = Co(ll) or Ni(ll)

The products remain the same even if [Cu(en)2]Cl2 is allowed to

react with C0CI2, NiCl2, indicating that the triphenylphosphine molecule has

been replaced by the ionic chlorides of the precursor. The quantitative

estimation of chloride ion as AgCI confirms the presence of four chloride

ions in all the bimetallic species.

32

The magnetic moment values and electronic spectral bands and

their assignments for the complexes are given in Table IV. All the Cu(ll)

complexes showed a broad d-d absorption band at about 627 nm

assigned to the Tag <- Eg transition which is characteristic of an

octahedral copper(ll) ion. * Stephens has also reported a distorted

octahedral geometry for the Cu(ll) complex with diethylenetriamine.^ The

position of d-d band remains unaltered while the absorption band in the UV

region slightly varies for all of the bimetallic complexes. The absorption

band at about 350 nm is unambiguously attributed to the charge transfer

M" •»— Cr, revealing the presence of MCU " species, in accord with the

observations^^ reported for CuCU '. It is clear that the position of charge

transfer band is red shifted as the size of zinc group metal increases.

The magnetic moment values of the mononuclear and all the

binuclear complexes, excepting [Cu(dien)2][CuCl4] falls in the 1.89 to 1.97

BM range, corresponding to one unpaired electron of copper(ll) ion. This

suggests that there is no remarkable influence of the d ° system of zinc,

cadmium and mercury on the single unpaired electron available on the

copper(ll) ion. Since the copper(ll) ion is a d^ system, the observed value

should correspond to one unpaired electron. The observed magnetic

moment for [Cu(dien)2][CuCl4] is 2.47 BM, which lies between the

calculated value for one and two unpaired electrons but the tendency is

more toward the latter. Since the complex contains two copper(ll) ions Hetr

33

Cua2-2H20 + 2H2N. .NH.

H2N.

HjN

Cu' ,NH2

NH,

CI.

MCI.

2@

MCL 2e

Fig. 3. Synthesis of bimetallic complexes

34

X <D CL

E o

\ j

o ^ * o (/)

(0 c

u

a> u C CO

3 TD O o k4 CS

(0

c

E 111 TJ C CO C/)

_o w

' l _ 0} o

O 75 o "w

u o

t/1

o

o

. f3

o

CO

a.

</3

X

a o U

o e

o

U

oo o

vq

CN

(N

(N

0 0 <N

(N

u 'a' (U

u

o o m

OS

OS

as ON

<N O tN

OO 0 \

OS oo

0 \ as (N

OS IN

i n

so

as as

o (N

as

OS

^ ^ c3 ^ ^ •^ J3 Q 43 ffl

J -

u u

3

u

u a N

I

<N

• * '

O N

-^

00 «n

o NO

OS

o6

oo

NO

s

-3-U

u

 — 1

o NO 1 - H

NO

J 3 (U

a>

"c 0} E o

C

T3 C TO (0 C .o * (0 c (0 H o 'c 2 o

LU

« 0) o c 0) 3 CT

Ct

OJ

C/5

<u o c u IT

H PL,

O 4 -

c S o

o c o l-H o u i3

c o

• 4 - *

'e/3

C CO i-i

H

I S

2 i

3

u o

w o

U -T

u a

OQ

"E, S o U

0^ OO

- fS 0\ en

0^

00

JJ 1

i DO

1

00

M (N

i 00 H

ea

m (N

i 00 H

H U

00

m rs i

00 H U

00

w fS

i 00 H

H U

r <N v£)

SO (N r

<o <N VO

(N VO m

^ (N VO

m r-m

r-~ CM VO

00 OO m

o ^-H

m

_ ( t (N

1—1

»o (N

Tf en CN

o o OO

o OO

o o o

U

3

u

g 3

u c N

.a

CJ

- 7 U

u

a (U

3 U

OS O

OO Tf •*

»-H

r-Tj-

,—1

•* • ^

o\ m • ^

«n >r) Tj-

o

VO fN cn m

«n en »—( m

<n m ts ro

00 *-H

cs m

(N OS <S fn

(N (N (N m

m t cs m

m en <s m

<N o tn en

r~-Tf «N m

u

u

value is expected to correspond to two unpaired electrons. However, 2.47

BM value is lower than expected and suggests that the complex ions are

not arranged in a regular- tetrahedral manner leading to zero orbital

contribution to magnetic moment value. Since the anionic part has

distorted tetrahedral geometry the [Cu(dien)2] "' unit also complies with the

same degree of distortion in geometry.

It is difficult to distinguish NH frequency from NH2 frequency

because they fall nearly in the same region. The IR spectrum of the free

dien molecule exhibits two bands (3360-3295 cm' ), which are shifted to

lower wave number after chelatio-n (3135-3247 cm" and 3235-3326 cm' ).

Two sharp absorption bands at 1013 to 1085 and 1439 to 1455 cm" are

due to v(C-C) and v(C-N) modes, respectively. A sharp peak at about 500

cm" is assigned to v(Cu-N). All the bimetallic complexes show similar

spectra, except that one additional IR band is observed in the 234-310

cm" range, associated with the metal chlorine stretching frequency of the

MCl4 " moiety.

EPR spectra of the precursor [Cu(dien)2]Cl2 and bimetallic

complexes were studied and the following inferences were drawn. The

spectra of [Cu(dien)2]Cl2, [Cu(dien)2][CuCl4] and [Cu(dien)2]lCdCl4]

complexes at room temperature showed a strong signal and their g||, gi

values have been calculated. The complexes did not show hyperfine

37

structure at room temperature. It may be attributed to strong dipolar and

exchange interaction between copper(ll) ions in the unit cell. The room

temperature g values of [Cu(dien)2]Cl2 (g|| = 2.052 and gi = 2.118),

[Cu(dien)2][CuCl4] (g|| = 2.11 and gi = 2.035), and [Cu(dien)2][CdCl4]

(gil = 2.215 and gi = 2.0523) indicated a tetragonal environment for the

Cu(ll) ion in each case. As g|| > gi for [Cu(dien)2][CdCl4] and

[Cu(dien)2][CuCl4] the ground state wave function is indicated to be dx%^

but for the complex [Cu(dien)2]Cl2, g± > g|| suggests that dz may be the

ground state. It means that the ground state changes sharply during the

formation of bimetallic complexes.

In the EPR spectra, the peak width can be explained by the

magnetic dipolar interaction with the neighbouring Cu(ll) ions if we

suppose that there are four Cu(ll) ions in the immediate neighbourhood

surrounding the central Cu(ll) ion or each Cu(ll) ion will interact

magnetically with the four other nearest Cu(ll) ions. According to the well

known Van-Vleck formula^^ for polycrystalline samples connecting line

width with distance between the lines we have

( A V = 3/5g*p'*h-'s(s+1)Ikr^jk

where the symbols have their usual meanings, and in the summation

sign j represents the central ion and k runs from 1 to 4 corresponding to

four nearest Cu(ll) ions. But Van VIeck formula is correct if there is only

38

one signal in the EPR spectrum. In our case, two signals were obtained

corresponding to gi and gi|. Using the method discussed in the book, ^ the

real width of the two signals was evaluated and then Van VIeck formula

was applied. The distance (Cu-Cu) comes out to be rjk = 6.24, 5.87 and

6.92 A° for [Cu(dien)2]Cl2, [Cu(dien)2][CuCl4] and [Cu(dien)2][CdCl4]

complexes respectively. The Cu-Cu distance in all the three complexes is

significantly higher which means that Cu does not form a M-M bond in all

the three complexes. Further support comes from magnetic moment

values. If the two Cu ions form a metal-metal bond the odd electrons will

be paired and the complex will be diamagnetic. If they do not form a bond

then the complex will be paramagnetic. All the three complexes are

paramagnetic but the magnetic moment value for [Cu(dien)2][CuCl4]

complex measured at 25 °C is 1.23 BM per Cu atom, rather than the spin

only value of 1.73 BM. This suggests that there is a weak Interaction or

weak coupling of the unpaired spins on the two Cu atoms in this

complex. ^

Thermal analysis of [Cu(dien)2][CuCl4] was studied in the

temperature range 25-1000°C, using a combined thermogravimetric

analyzer and differential thermal analyzer.

The thermogram of [Cu(dien)2][CuCl4] can be divided into two major

portions showing weight loss of various components. The first step shows

the weight loss of about 42.93% in the temperature range of 226 to 484°C

39

which compares well with the calculated value of 43.36% corresponding to

two dien moiety. The second step runs steeply from 484 to GGd'C showing

a weight loss of nearly 42.65% which is equal to the anionic CuCi/" portion

(43.22%). In the end, the residue left is copper metal (13.36%).

The DTA studies show that both the decomposition of organic

moiety and anionic part are exothermic processes.

40

REFERENCES

1. G. Davey and F. S. Stephens, J. Chem. Soc. (A), 1971, 103.

2. G. Schwarzenbach, Helv. Chim. Acta., 1952. 35, 2344.

3. R. D. Hancock, J. Chem. Educ, 1992, 69, 615.

4. D. R. Rosseinsky, J. Chem. Soc. Dalton Trans., 1979, 732.

5. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5"" Edition, John Wiley & Sons, New York, 1988.

6. F. A. Cotton and R. M. Wing, Inorg. Chem., 1965, 4, 314.

7. F. S. Stephens, J. Chem. Soc. (A), 1969, 883.

8. B. J. Hathaway, Coord. Chem. Rev., 1970, 5,143.

9. R. R. Holmes, Prog. Inorg. Chem., 1984, 32, 120.

10. M. Bacci, Chem. Phys., 1986,104, 191.

11. M. I. Arriortua, J. L. Mesa, T. Rojo, T. Debaerdemaeker, D. Beltran-Porter, H. Stratemeier and D. Reinen, Inorg. Chem., 1988, 27, 2976.

12. D. Reinen and M. A. Atanasov, Chem. Phys., 1989,136, 27.

13. R. Alimann, M. KrestI, C. Bolos, G. Manoussakis and G. St. Nikolov, Inorg. Chim. Acta., 1990,175, 255.

14. C. Bazzicalupi, A. Bencini, E. Berni, A. Bianchi, C. Giorgi, V. Fusi, B. Valtancoli, C. Lodeiro, A. Roque and F. Pina, Inorg. Chem., 2001, 40,6172.

15. M. J. Bew, R. J. Fereday, G. Davey, B. J. Hathaway and F. S. Stephens, Chem. Commun., 1970, 887.

16. W. J. Geary, Coord. Chem. Rev., 1971, 7, 81.

17. M. C. Jain, A. K. Srivastava and P. C. Jain, Inorg. Chim. Acta., 1977, 23, 199.

41

18. D. Kivelson and R. R. Neiman, J. Chem. Phys., 1961, 35,149.

19. J. C. Bailer Jr and D. H. Busch, Chemistry of the Coordination Compounds, Reinhold Publishing Corp., New York, 1956, p5.

20. M. Gerken, P. Kolb, A. Wegner, H. P. A. Mercier, H. Borrmann, D. A. Dixon and G. J. Schrobilgen, Inorg. Chem., 2000, 39, 2813.

21. W. J. Casteel, P. Kolb, N. LeBlond, H. P. A. Mercier and G. J. Schrobilgen, Inorg. Chem., 1996, 35, 929.

22. E. Colacio, R. Kivekas, F. Lloret, M. Sunberg, J. Suarez-Varela, M. Bardaji and A. Laguna, Inorg. Chem., 2002, 41, 5141.

23. A. I. Vogel, Text Book of Quantitative Inorganic Analysis, Longmans Group, England, 1986, p507.

24. P. V. Bernhardt, E. G. Moore and M. J. Riley, Inorg. Chem., 2001, 40, 5799.

25. G. Marcotrigiano, L. Menabue, G. C. Pellacani and M. Saladini, Inorg. Chim. Acta., 1979, 34, 43.

26. L. A. Blumenfeld, V. V. Voevodski and A. G. Semenov, Application of EPR in Chemistry (in Russian), Siberian Sector, Academy of Sciences, U.S.S.R.. 1962, p79-85.

27. L. A. Blumenfeld, V. V. Voevodski and A. G. Semenov, Application of EPR in Chemistry (in Russian), Siberian Sector, Academy of Sciences, U.S.S.R., 1962, p105-110.

28. J. D. Lee, Concise Inorganic Chemistry, Fifth edition, Blackwells Science Ltd., Oxford, 1996, p829-30.

42

CHAPTER III

NOVEL N4 MACROCYCLES AND THEIR TRANSITION

METAL CHELATES

NOVEL N4 MACROCYCLES AND THEIR TRANSITION METAL CHELATES

The coordination chemistry of macrocyclic ligands is a fascinating

area of study for inorganic chemists. " Tetraazamacrocyclic ligands are of

special interest, as the coordinating side chains may increase the stability

of the metal complexes and tune the selectivity between various metal

ions. " The coordination properties of macrocycles bearing pendant

groups have attracted great deal of attention. "® Pendant groups are used

to attach substrates covalently to enforce specific oxidation states and

coordination geometries and to influence the strength of the ligand field.

The crystal and molecular structure of [3-(4-pyridiniumcarbonyl)-

1,3,5,8,12,-pentaazacyclotetradecane]- nickel(ll) has been reported^ in

which pyridine acts as pendant group. Template reactions and in situ

method have been used extensively for the easy, high yielding and

stereospecific synthesis of complex ligand molecules. A metallocyclam

subunit has been appended to pyridine through a metal template

procedure which involves the condensation of amides of 3- and 4- pyridine

carboxylic acid with formaldehyde and the nickel(ll) complex with the open

chain tetraamine. These metallocyclam units act as building blocks of

supramolecular system and act as two-electron redox systems. In the

43

recent past, a 36-membered macrocycle with four ethylenediamine entities

has been reported.^°

The synthesis of transition metal complexes with macrocycles

containing a variety of functional groups on the periphery has been

reported." These groups have been termed superstructures. Such

compounds are of particular importance in view of their use in the

treatment of malignant tumors. ^ Increasing interest has been shown in the

design of new macrocycles with predetermined guest complexation.^^ In

view of these observations it was considered worthwhile to investigate in

detail, the synthesis of four tetradentate macrocycles and their chelates

with transition metal ions.

EXPERIMENTAL

4-Aminoantipyrine, ethylenediamine, 1,3-diaminopropane, 1.6-

diaminohexane (Koch Light) ethyl acetoacetate (S.D. Fine chemicals),

acetylacetone, benzoylchloride, and hydrated metal chlorides (BDH) were

used as received. Benzoylacetic acid was synthesized and recrystallized

by the literature method. Elemental analyses were carried out with a Carlo

Erba 1106 analyser. The metals were determined by complexometric

titration using EDTA and CI was determined gravimetrically. The IR

spectra (4000-200cm'') were recorded on a 621 Perkin-Elmer grating

spectrometer as KBr disc. The electronic spectra were recorded in DMSO

44

on a Carl-Zeiss VSU2P spectrophotometer. Magnetic susceptibility

measurements were done with an Allied Research model 155 vibrating

sample magnetometer and the molar conductances were measured at

room temperature using a Systronlcs 321 conductivity bridge.

Synthesis of L and L

To a solution of 4-aminoantipyrine (20 mmol, 4.06 g) dissolved in

100 mL of hot ethanol, acetylacetone (10 mmol, 1.03 mL) was added and

the mixture was refluxed for half an hour in a round bottom flask. On

cooling this mixture to room temperature, a light-orange precipitate was

obtained (Fig.1). It was redissolved in THF (100 mL) and

1,3-diaminopropane (10 mmol, 0.85 mL) (for L ) or 1,6-diaminohexane

(10 mmol, 1.16 g) (for L ) were then added and the mixture was again

refluxed for about 10 h. It was then cooled to 0 "C and an excess of 0.1

molar HCI (20 mL) was added to cause precipitation. The product was

thoroughly washed with diethyl ether and dried in vacuo. Yield, 1.27 g for

L (25%) and 1.48 g for L (27%).

Synthesis of L^and L

A mixture of 4-aminoantipyrine (20 mmol, 4.06 g) and

ethylenediamine (10 mmol, 0.66 mL) (for L ) or 1,3-diaminopropane

(10 mmol, 0.85 mL) (for L"*) in 100 mL ethanol was refluxed for about 20 h.

It was cooled to 0 °C and acidified with 20 mL of 0.1 molar HCI which

45

afforded a brown product. It was redissolved in hot ethanol (100 mL) and

benzoylacetic acid (20 mmol, 3.2 g) was added to it .It was further refluxed

for about 30 h and then cooled to 0 °C followed by the addition of 0.1 molar

(20 mL) HCI which yielded a precipitate (Fig. 2). It was washed thoroughly

with ethanol and dried in vacuo. Yield, 1.81 g for L (25%) and 1.7 g for L'*

(23%).

General Methods for the Synthesis of Complexes

Initially we tried to synthesize the complexes by adding the metal

salts to ligand solution, however the yields were very poor (10 to 15%). To

overcome this problem, the complexes were synthesized in situ, in which

salts were immediately added to the solution of the ligands under

preparation.

Acetylacetone (2 mmol, 0.20 mL) was added dropwise to an

ethanolic solution (50 mL) of 4-aminoantipyrine (4 mmol, 0.80 g). After

refluxing this mixture for about half an hour 1,6-diaminohexane (2 mmol,

0.23 g) was added and further refluxed for 24 h. The mixture was then

cooled to 0 °C and hydrated metal chloride (2 mmol) in ethanol (25 mL)

was added which afforded brisk precipitation of coloured complexes. It was

filtered, washed with cold ethanol and dried in vacuo.

46


A mixture of 4-aminoantipyrine, acetylacetone and

1,3-diaminopropane or 1,6-diaminohexane was refluxed. It was cooled to

0 °C and an excess of dilute HCI was added to cause precipitation of L

and L as shown in Fig. 1.

For the synthesis of L and L , a mixture of 4-aminoantipyrine,

1,3-diaminopropane or ethylenediamine was refluxed for 20 h. It was

cooled to 0 "C and precipitated with dilute HCI. This product was dissolved

in ethanol and refluxed with benzoylacetic acid. Addition of dilute HCI

afforded the ligands L^and L' CFig. 2).

Metal complexes were synthesized directly by the addition of

hydrated metal chloride solution to the ligand solution in the same solvent.

Since the yield of the complexes was too poor (10 to15%), in situ method

was employed. In this method the ligand was not isolated. The metal

chloride was added to the solution of the ligand under preparation.

Elemental analyses of the complexes correspond to the

compositions MLCb and M'LCb where M = Mn(ll), Co(ll), Ni(ll), Cu(ll) and

Zn(ll) and M' = Cr(lll) and Fe(lll). The molar conductance measured in

DMSO (15-42 ohm' cm^mole'"') indicated that the divalent metal complexes

are non electrolytes '' while those of M(lll) ions are 1:1 electrolytes

(Table I).

47

It has been observed by many workers^^^^ that in Schiff base

macrocyclic complexes the C=N stretching frequency appears in the

1620-1660 cm" region. A comparison of the IR spectra of the free

macrocycles with those of their complexes indicated a substantial shift in

v(C=N) and v(C-N) (Table II). The presence of v(NH) in L and L'' and their

complexes has been supported by the appearance of a band in the

3080-3230 cm' region. It is interesting to note that v(COOH) consistently

appears at 1430 cm' in both the free (L^and L'*) and chelated macrocycles

which implies that the pendant group is not coordinated in any case

although macrocycles having pendant donor groups that are capable of

coordinating with the central metal ions are known. ^

Some 'scorpiand' type molecules are also reported having H2N-CH2

'tails' to a tetraamine macrocycle."" The far IR spectra of the complexes

show intense halogen-sensitive absorptions in the 255-300 cm' region.

The bands in the 320-390 cm' range are assigned to v(M-N) vibrations. A

band at 1070 cm" in all the ligands and complexes is assigned to v(N-N)

in pyrazole.

The magnetic moment values and electronic spectral bands are

given in Table III. The spectra of Co(ll) complexes with L\ L , L and L'*

have identical features, indicating that the stereochemistry around the

Co(ll) ion in solution are alike. An octahedral Co(ll) species exhibits three

48

H.C NH2

o o -N.

H3C" ^K ^ O

H3C CH2 \ c H 3

EtOH -2H2O

H3C CH3

H3C. /N N ^ CR3

" ^ ^ ^ ^

H2N NH2

Ice EtOH

j -2H2O

H3C. CH3

HjC^,. ^ N N ^ ^ CHi

n = OforL' 2

and n = 3 for L ' \ ; ^ V^

1 2 Fig. 1. Synthesis of Ligands L and L

49

H,C \

+ H2N NH2

"V^ Ice EtOH -2H2O

H,C

N

NH2 H2N CH3

N.

\ C/n

+ V^

2 C6H5\ CH2COOH C II O

EtOH Ice

, r -2H20

H5C6 H

H,C

COOH C6H5

-N

CH2COOH

N C " CH3

H3<- N N N

A ^" A N ^ CH3

n^OforL^

and n = 1 for L V X

Fig. 2. Synthesis of Ligands L and L

50

L ' or L^ (prepared in situ)

H3C

+

MCU

EtOH

H,C

N N

n = OforL' n = 3 for L

M = Mn(II), Co(II), Ni (II), Cu(II) and Zn(II)

CH3

N CI N

N CI N

CH3

N"^ CH3

L^ or L'* (prepared in situ)

HiC

MCln

H^ COOU HsCfi^ . X /C6H5

n = 0 for L' n = 1 for L"

CH2COOH N CI N C ^ CH3

• C l ^ <

M = Mn(II), Co(II), Ni (II), Cu(II) and Zn(II)

A ^" >. N-^ CH3

1 T 2 T 3 Fig. 3. Synthesis of Complexes of Ligands L , L , L and L

51

L ' or L^ (prepared in situ)

n = OforL'

n = 3 for L M' = Fe(III), Cr(III)

H,C.

+

M'CU

EtOH

H3C

N H3C- \ N

CH^

.N CI N X I y ^ M ' ' ^

N CI N

- <

CH3

N N ^ ^CH3 CI

L^ or L^ (prepared in situ)

n = 0 for L^

n = 1 for L

M' = Fe(III), Cr(III)

H3C

M'CU

H5C6 H

H3C -;N

,N CI N

X IX N CI

COOH C6H5 CH2COOH

= <

CH3

^ ^ ^ " ^

N N ' "CH3

CI

Fig. 4. Synthesis of Complexes of Ligands L , L , L and L

52

CO

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transitions. We, too, have observed three absorption bands at 22,988 cm"\

18,018 cm-'" and 12,987 cm"'' for [Co(U)Cl2], 22,988 cm-\ 19,047 crrT'' and

12.048 cm- for [Co(L^)Cl2], 21,978 cm-\ 18,018 cm-'' and 12,987 cm^ for

[Co(L )Cl2] and 21,052 cm-\ 19,047 cnT'' and 10,989 cm"'' corresponding to

''Tig(P)^'Tig(F), %g(F)^^Tig(F) and %(F)^^Tig(F) transitions,

respectively. These bands in the visible region are consistent with spin

allowed d-d transition for a six coordinate octahedral Co(ll) ion. The

magnetic moment value of Co(ll) complexes with L\ L^, L^ and L'' is very

low which is probably due to an equilibrium between low and high spin

states of Co(ll). However, the electronic bands and the pink colour of the

complexes are consistent with an octahedral environment around cobalt(ll)

ion.

Three bands characteristic of octahedral Ni(ll) ion in a high-spin

state are anticipated. ® In the present case, the bands are observed at

27,027 cm-\ 23,809 cm" and 13,986 cm-"" for [Ni(L^)Cl2]. 25,974 cm-\

16,000 cm- and 11,111 cm"" for [Ni(L2)Cl2], 25,974 cm-\ 22,988 cm-"" and

13,986 cm- for [Ni(L )Cl2] and 27,777 cm-\ 24,096 cm" and 13,986 cm"

for [Ni(L )Cl2] corresponding to ^Tig(P)^%g(F), ^Tig(F)^%g(F) and

T2g(F)'«— A2g(F) transitions, respectively. The electronic spectral bands

and the relatively low magnetic moments suggest a distorted octahedral

geometry for Ni(ll) ion.

65

The observed magnetic moment values for chromium(lll) complexes

are close to that calculated for a d^ ion, corresponding to an octahedral

geometry.

The magnetic moment for all of the manganese(ll) complexes

ranges between 5.98 - 6.12 BM which correspond to a high-spin

octahedral structure for the metal ion. ^

The iron(lll) complexes exhibit three bands. In the high-spin

complexes the theoretical magnetic moment value is 5.91 BM. We have

obtained, for these complexes, values in the range for a high-spin

octahedral geometry for the Fe(lll) ion. °

The copper{ll) complexes show one or two charge transfer bands.

The band exhibited in the 11,235 -13,157 cm" region is assigned to the

^T2g<- Eg transition which is characteristic of an octahedral copper(ll) ion.

The magnetic moment value also supports the above geometry.

66

REFERENCES

1. K. Motoda, H. Sakiyama, N. Matsumoto. H. Okawa and S. Kida, Bull. Chem. Soc. Jpn., 1992, 65, 1176.

2. C. Lodeiro, A. J. Parola, F. Pina, C. Bazzicalupi, A. Bencini, A. Bianchi, C. Giorgi, A. Masotti and B. Valtancoli, Inorg. Chem., 2001, 40, 2968.

3. E. V. Rybak-Akimova and K. Kuczera, Inorg. Chem., 2000, 39, 2462.

4. N. F. Curtis, C. E. F. Rickard and J. M. Waters, Aust J. Chem., 2000, 53, 945.

5. S. C. Rawie, A. J. Clarke, P. Moore and N. W. Alcock, J. Chem. Soc. Dalton Trans., 1992, 2755.

6. M.J. Gunter and B. C. Robinson, Aust. J. Chem., 1990, 43,1839.

7. M. B. Inoue, C. A. Viliegas, K. Asano, M. Nakamura, M. Inoue and Q. Fernando, Inorg. Chem., 1992, 31. 2480.

8. N. W. Alcock, K. P. Balakrishnan, A. Berry, P. Moore and C. J. Reader, J. Chem. Soc. Dalton Trans., 1988, 1089.

9. A. D. Bias, G. D. Santis, L. Fabbrizzi, M. Licchelli. A. M. M. Lanfredi, P. Pallavicini, A. Poggi and F. Ugozzoli, Inorg. Chem., 1993, 32, 106.

10. T. Shimada, M. Kodera, H. Okawa and S. Kida, J. Chem. Soc. Dalton Trans., 1992, 1121.

11. J. H. Cameron, H. B. Harvey and I. Soutar, J. Chem. Soc. Dalton Trans., 1992, 597.

12. D. Parker, Chem. Soc. Rev., 1990,19, 271.

13. R. M. Izatt, J. S. Bradshaw, K. Pawlak, R. L. Bruening and B. J. Tarbet, Chem. Rev., 1992, 92, 1261.

67

14. W. J. Geary, Coord. Chem. Rev., 1971, 7, 81. 15. M. G. B. Drew, A. H. Binothman, S. G. Mcfall, P. D. A. Mcllroy and S.

M. Nelson, J. Chem. Soc. Dalton Trans., 1977,438.

16. F. C. J. M. V. Veggal, S. Harkema, M. Bos, W. Verboom, C. J. V. Staveren, G. J. Gerritsma and D. N. Reinhoudt, Inorg. Chem., 1989, 28,1133.

17. B. K. Daszkiewicz, J. Chem. Soc. Dalton Trans., 1992,1673.

18. K. K. Nanda, R. Das, M. J. Newlands, R. Hynes, E. J. Gabe and K. Nag, J. Chem. Soc. Dalton Trans., 1992, 897.

19. J. Lewis and R. G. Wilkins, Modern Coordination Chemistry Interscience, Newyork, 1960, p406.

20. C. J. Ballhausen, Introduction to Ligand Field Theory, IVlc Graw Hill, NewYork, 1962, p253.

68

CHAPTER IV

(A) SYNTHESIS AND CHARACTERIZATION OF

COMPLXES OF Mn(II), Fe(III), Co(II), Ni(II),

Cu(II) AND Zn(II) WITH

SCHIFF BASES DERIVED FROM ISATIN

AND POLYAMINES

SYNTHESIS AND CHARACTERIZATION OF COMPLXES OF Mn(ll), Fe(lll), Co(ll), Ni(ll),

Cu(ll) AND Zn(ll) WITH SCHIFF BASES DERIVED FROM ISATIN

AND POLYAMINES

2,3- Indolinedione also known as isatin has been found to be similar

to oxindole (2-indolinone)\ an endogenous polyfunotional heterocyclic^

compound exhibiting biological activity in mammals. Recently, it has been

shown that under acetylating condition, Schiff base derivative from isatin is

transformed to spiroheterocycles^. Keeping in view the medicinal and

biological properties of isatin and its derivatives, it was thought worthwhile

to synthesize and characterize complexes of transition metal ions with

Schiff bases derived from isatin and polyamines.

EXPERIMENTAL

1,2-diaminoethane (Fluka), diethylenetriamine (BDH), isatin (Reidel)

and hydrated metal chloride (BDH) were used as received. Elemental

analysis was carried out with a Carlo Erba 1106 analyser. CI was

determined gravimetrically. The IR spectra (4000-500 cm' ) were recorded

on a 621 Perkin-Elmer grating spectrometer as KBr disc. The conductivity

measurements were carried out with CM-82T Elico Conductivity bridge in

DMF. The electronic spectra were recorded on Cintra 5GBC

spectrophotometer in DMF. Magnetic susceptibility measurements were

69

done with 155 Allied Research Vibrating sample magnetometer at room

temperature. H NMR spectra were recorded on a Brucker Ac 250

spectrometer at 250 MHz, using TMS as a reference in DMSO-de. EPR

spectrum of copper complex was recorded on a RE-2X Jeol EPR,

spectrometer fitted with 100 KHz field modulation.

Synthesis of iigand L

Ethylenediamine (5 mmol, 0.33 mL) was added dropwise to isatin

(10 mmol, 1.47 g) dissolved in 50 mL hot methanol and the mixture was

refluxed for about 4-5 h. It was cooled to 0 °C and acidified with HCI

(1 mmol), which yielded a light yellow precipitate. It was washed with

methanol and dried in vacuo. Yield, 0.84 g (53%).

Synthesis of Iigand L

Diethylenetriamine (5 mmol, 0.54 mL) was added dropwise to isatin

(10 mmol, 1.47 g) dissolved in 50 mL hot methanol and the mixture was

refluxed for about 10 h. It was cooled to 0 °C and acidified with HCI

(1 mmol), which yielded a light yellow precipitate. It was washed with

methanol and dried in vacuo. Yield, 0.92 g (51%).

Synthesis of complexes of Iigand L

Ethylenediamine (5 mmol, 0.33 mL) was added dropwise to

methanolic solution (50 mL) of isatin (10 mmol, 1.47 g). After refluxing this

mixture for about half an hour hydrated metal chloride (5 mmol) was

added. 5 mL Buffer solution of pH 9.2 was also added and then refluxed

70

for 24 h. It afforded brisk precipitation of the complexes. The contents were

cooled to room temperature, filtered, washed with cold methanol and dried

in vacuo. Yield, (68-79%).

Synthesis of complexes of ligand L

Diethylenetriamine (5 mmol, 0.54 mL) was added dropwise to

methanolic solution (50 mL) of isatin (10 mmol, 1.47 g). After refluxing this

mixture for about half an hour hydrated metal chloride (5 mmol) was

added. 5 mL Buffer solution of pH 9.2 was also added and then refluxed

for 24 h. It afforded brisk precipitation of the complexes. The contents were

cooled to room temperature, filtered, washed with cold methanol and dried

in vacuo. Yield, (60-70%).


The Schiff bases were synthesized by refluxing a 2:1 mixture of

isatin and ethylenediamine (L ) or diethylenetriamine (L^). However, the

complexes were synthesized by template reaction by refluxing all the three

ingredients, isatin, polyamines and hydrated metal chlorides in methanol.

All the complexes are stable in air and decompose at high temperature.

They are highly soluble in DMF and DMSO. The molar conductance

measured in DMSO (10-35 ohm' cm^mole""") indicated that the divalent

metal complexes of ligand L are non electrolytes^ while those of ligand L

are 1:1 electrolytes (62-79 ohm' cm^mole"^).

71

+ HN 2 & ^

H

Ice MeOH

I -2H2O

9. 9

MCL

M = Mn(ll), Co(ll), Ni(ll), Cu(ll) and Zn(ll)

Fig. 1. Synthesis of metal complexes of ligand L

72

@;x: HN 2

NH H

MCln

10' 11 10 H X \ 9

CI

M = Mn(ll), Co(ll), Nl(ll), Cu(ll) and Zn{ll)

Fig. 2. Synthesis of metal complexes of ligand L

73

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Fe

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74

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The IR spectra of the free ligands and their complexes are listed in

Table II. The free ligands L and L show characteristic bands for v(C=0)

at 1732 cm' and 1735 cm"\ respectively. The bands at 1651 cm" and

1639 cm" may be due to C=N stretches of ligands L and L respectively.

In all the complexes, the v(C=0) was shifted by 10 to 25 cm" to lower

frequencies, due to the coordination of the C=0 groups. Also, the v(C=N)

bands were shifted by 20 to 30 cm' to lower frequencies, due to its

participation in coordination. A broad band at 3259 cm' may be assigned

to the stretching frequency of intramolecular hydrogen bonded v(NH) in L

and the band at 3260 cm""* in the spectrum of L may be assigned to the

v(NH) of the indole part. The N-H stretching vibration was not significantly

affected in all complexes which indicates that it is not involved in

coordinating to the metal ion. The free L exhibits the v(N-H) at 3388 cm"

which undergoes a negative shift of about 50 to 80 cm" range as a

consequence of coordinating of N atom with the metal ion.^ The L thus

acts as a pentadentate ligand while ligand L acts as a neutral tetradentate

ligand coordinating with its two carbonyl oxygen atoms and two

azomethine nitrogen atoms.

The magnetic moment values and spectral bands are given in

Table III. The electronic spectra of the Mn(ll) complexes showed two

ligand field bands in the region 21,598-22,223 and 17,513 cm'

80

corresponding to '*T2g(G)-i-%g and '*Tig(G)-<-%g transitions, respectively.

These bands are consistent with an octahedral geometry around the Mn(ll)

ion/ The magnetic moments of [Mn(L )Cl2] and [Mn(L^)CI]CI are 5.52 and

5.48 BM, respectively. These values are slightly lower as compared to high

spin Mn(ll) complexes. This can be attributable to the spin exchange in the

solid state.

The electronic spectral bands for [Fe(L )Cl2]CI and [Fe(L )CI]Cl2 are

observed at 23,474 and 25,000 cm'\ respectively. The weak band is not of

much help in deciding the transitions although the magnetic moment (5.87

and 5.9 BM) is indicative of a high spin octahedral geometry for the Fe(lll)

ion.^

The electronic spectra of the cobalt(ll) complexes exhibited two

ligand field bands in the region 17,513-20,920 and 22,026-22,988 cm""

which may be ascribed to %g(F)<-'*Tig(F) and ^Tig(P)<-^Tig(F) transitions,

respectively. These bands correspond to an octahedral geometry around

the cobalt(ll) ion. The observed magnetic moment values for the cobalt(ll)

complexes fall in the range expected for three unpaired electrons^^°

(Table III).

The Ni(ll) complexes exhibit three bands in the region 12,195-

12,445, 17,513-17,921 and 24,390-25,316 cm' which may reasonably be

assigned to % ( F ) ^ X ( F ) , 'T ig(F)^X(F) and 'Tig(P)^%g(F)

transitions, respectively. The [Ni(L )Cl2] and [Ni(L^)CI]CI complexes show a

81

Peff. value of 3.12 and 3.09 BM respectively, which is expected for a six

coordinate Ni{ll) complex. ^

The Cu(ll) complexes show one or two charge transfer bands. The

band appearing in 14,641-14,045 cm"'' region is assigned to the T2g<- Eg

transition. The observed room temperature magnetic moment of

[Cu(L )Cl2] and [Cu(L^)CI]CI is 1.83 and 1.78 BM, respectively, which

correspond to the presence of single unpaired electron. The position and

width of the band indicates distorted octahedral geometry. ^ The proposed

structures of the metal chelates are shown in Fig. 1 and 2.

The EPR spectrum of the polycrystalline complex [Cu(L )Cl2] at room

temperature showed a strong signal and its g||, g i and axial symmetry

parameter (G = g||-2/gj.-2) has been calculated. The complex did not show

hyperfine structure at room temperature. This may be attributed to strong

dipolar and exchange interaction between copper(ll) ions in the unit cell.

The room temperature g values are g|| = 2.28 and gx = 2.089 which

suggest that dx%^ may be the ground state for the complex.

The G value measures the exchange interaction between copper

centers in the polycrystalline solid. If G > 4, exchange interaction is

negligible and if G < 4, considerable exchange interaction occurs in the

solid complexes. ^ For this complex the G value is 3.146, which indicates a

considerable exchange interaction in the complex.

82

In ligand L^ the ^H NMR gave signals at 66.7 to 7.8 (m, 8H,

aromatic protons), 610.3 to 11.1 (brm, 2H, Ni, Ni' protons) and 64.1

(ss, 4H, Cg, Cg protons).

In [Zn(L^)Cl2], the ^H NMR gave signals at 67.8 (d, 2H, J = 8.09, C7

and C7 protons), 67.4 (dd(t like), 2H, J(6,7) = 8.08 and J(6.5) = 7.32, Ce and

Ce protons), 67.0 {dd(t like), 2H, J(5,6) = 7.32 and J(5,4) = 8.04, C5 and C5

protons and 66.9 (d, 2H, J(4,5) = 8.04, C4 and C4 protons) are easily

ascribable to structure in Fig. 1. In the low field regions of the spectrum NH

group of indole part (2H) shows a singlet at 610.8. As expected, methylene

protons (4H) appear as multiplet at 64.3.

In ligand L^ the ^H NMR signals appear at 66.8 to 7.3 (m, 8H,

aromatic protons), 64.3 (s, 8H, Cg, C10, Cg and C10 protons), 69.8-11

(m, 3H, Ni, Ni' and Nn protons).

In complex [Zn(L^)CI]CI, the ^H NMR signals appear at 66.8 to 7.3

(8H, aromatic protons), 64.2 to 4.3 (m, 8H, Cg, C10, Cg' and C10 protons),

610.8(s, 2H, Ni, Ni' protons) and 610.1(m, 1H, Nn protons).

In view of the above values, it is clear that in complexes, the signal

corresponding to Ni and Ni protons are shifted upfield as singlet due to

weakening of hydrogen bonding which in turn is due to coordination of

oxygen atoms to metal ions. The signal corresponding to Nn proton is

shifted downfield in complex [Zn(L^)CI]CI due to strong deshielding of the

metal cation. The methylene protons in complexes show multiplet signal,

83

because the atoms are now fixed and do not rotate freely. Finally, the

aromatic protons did not show any change in the position of their proton

signals, it is ascertained that they are not involved in coordination. We,

finally conclude that in complexes the signals corresponding to each

proton become sharp and resolved because the atoms are now fixed and

the molecule has rigid structure as compared to that of the corresponding

ligand. Thus the H NMR spectra reinforce the conclusions drawn from the

IR studies.

84

CHAPTER IV

(B) SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES

OF SCHIFF BASE MACROCYCLIC LIGANDS AND

THEIR TRANSITION METAL CHELATES

SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES OF SCHIFF BASE MACROCYCLIC LIGANDS AND

THEIR TRANSITION METAL CHELATES

Complexes of metal ions with synthetic macrocycles assume

importance due to their resemblance with many naturally occurring

systems and also because they are capable of furnishing an environment

of controlled geometry. Schiff base metal compounds have been widely

studied because of their applications in biological systems.""* For example,

manganese complexes involving tetradentate Schiff base derivatives are

most versatile and interesting synthetic systems. ^ Thus some of these

types of complexes were found to be artificial mimics of the biological

enzymes such as Mn-catalase^ , Mn-superoxidedismutase, Mn-

ribonucleotide reductase and in particular, the Mn-peroxidase that protects

cells against hydrogen peroxide induced oxidative stress. It has been

observed that the catalytic activity of the Schiff base complexes is very

sensitive to minor structural changes. Recently, photophysical and catalytic

properties of the complexes of Schiff base ligands have been sdtudied.^^

In the literature, several Schiff base ligands have been reported and

their coordination chemistry with a number of metal ions has been

extensively investigated.^° Most recently, pentadentate (N3O2) ligands with

several ring substituted salicylaldehydes have been prepared and their

85

coordination chemistry with a variety of metal ions has been thoroughly

explored. ^

In the last decade, Schiff base ligands have received more attention

mainly because of their wide application in the field of synthesis and

catalysis. ^ The attraction is still growing, so that a considerable research

effort is today devoted to the synthesis of new Schiff base complexes with

transition^" and main group metal ions^ to further develop applications in

both catalysis and material chemistry. ^

We report in this communication a series of complexes of metal ions

with N4 Schiff base macrocycles derived from the condensation of

triethylenetetramine with benzil (L'') and acetylacetone (L®).

EXPERIMENTAL

Benzil, acetylacetone (Fluka) triethylenetetramine (Ranbaxy) and

hydrated metal chlorides were used as received. Elemental analyses

(C, H, N) were carried out with a 1106 Carlo Erba analyzer. Chlorine was

determined gravimetrically. IR spectra (4000-400 cm' ) were recorded on a

RXI FT-IR spectrometer as KBr disc. The conductivity measurements were

carried out with CM-82T Elico conductivity bridge in DMF. The electronic

spectra were recorded on a Cintra 5GBC spectrophotometer in DMF.

Magnetic susceptibility measurements were done with a 155 Allied

Research vibrating sample magnetometer at room temperature. ^H NMR

86

spectra was recorded on a Bruker ACF 300 spectrometer at 300.12 MHz,

using TMS as a reference in DIVISO-de. EPR spectra of polycrystalline

sample was recorded on a RE-2X Jeol EPR, spectrometer fitted with 100

KHz field modulation. The TG was performed with a Rigaku TG 8110

thermal analyzer. The experiment was done in nitrogen atmosphere using

calcinated AI2O3 as reference material. The weight of the sample taken

was 10 mg and the heating rate was 10°C min'\

Synthesis of ligand L

To a hot methanolic solution (100 mL) of benzil (2.1 g, 10 mmol),

triethylenetetramine (1.5 mL, 10 mmol) was added and the mixture was

refluxed over waterbath for 3 to 4 h. It was left overnight at room

temperature, which yielded light yellow precipitate. It was filtered, washed

thrice with cold methanol and dried in vacuo. Yield, 1.86 g (58%).

Synthesis of ligand L

Acetylacetone (1.03 mL, 10 mmol) was taken in 100 mL of hot

methanol and triethylenetetramine (1.5 mL, 10 mmol) was added to it. The

mixture was then refluxed for half an hour and was left overnight at room

temperature which yielded a light orange precipitate. The product was

filtered, washed with cold methanol and dried in vacuo. Yield, 1.12 g

(53%).

87


Triethylenetetramine (1.5 mL, 10 mmol) was added dropwise to a

methanolic solution (50 mL) of benzil (2.10 g, 10 mmol). After refluxing this

mixture for about half an hour, hydrated metal chloride (10 mmol) was

added and further refluxed for about 4 h. The complexes were obtained

under reflux. The contents were cooled to room temperature, filtered,

washed with cold methanol and dried in vacuo. Yield, (63-76%).


Triethylenetetramine (1.5 mL, 10 mmol) was added dropwise to a

methanolic solution (50 mL) of acetylacetone (1.03 mL, 10 mmol). After

refluxing this mixture for about half an hour, hydrated metal chloride

(10 mmol) was added and further refluxed for about 4 h, which afforded

coloured complexes. It was filtered, washed with cold methanol and dried

in vacuo. Yield. (56-79%).


The ligands were synthesized by refluxing a mixture of

triethylenetetramine with benzil (L ) and triethylenetetramine with

acetylacetone (L®). The contents were left overnight which yielded the

ligand. However, the complexes were synthesized by the template method.

The low molar conductance of divalent complexes in DMF solution

indicated their non-electrolytic nature^ (Table IV).

88

H \ -N NH2

/ N NH2

H

%c/^*

c/' ^c^,

\i—I

H . /

-N N = a

(L^)

.C6H5

C6H5

MCb

CI

H \ I r-N \

N - C /

/ M

\ N=a

.C6H5

^C6H5

M = Mn(ll), Co(ll) and Cu(ll)

Fig. 4. Synthesis of complexes of ligand L

89

\\—I r—N NH2

/ N NH2

H

O O II II

^ CH3^ "CH2^ > H 3

M—I ^ N N=C- '

Me

Me

(L8)

MCh

CI

H \ I

H / I

\ N = C '

/ H.

N=a

.C6H5

CgHs

M = Mn(ll), Co(ll) and Cu(ll)

Fig. 5. Synthesis of complexes of ligand L

90

H \ -N NH2 ^C^

+

O ^ ^CfiHs

^ N • NH2

H ^ l I O ^ "^C,H5

H \

XeHs -N N = C '

H ^ I I C6H5

(L^)

FeCl

CI H

\ -N

\ N = C '

/

H / -N /

F ^

N=a

'C6H5

C6H5

Cl

CI

Fig. 6. Synthesis of Fe(lll) complex of ligand L

91

H r \ I

r—N

Ha

NH2

NH2 J

O O II II

+ CH3^ "CH2^ ^CH3

H \

Me -N N = C '

^ N N = a H / Me

(L8)

FeCU

CI H

\ -N

\ N=C'

H / I

/ N=a

.CeHs

^CgHs

CI

CI

Fig. 7. Synthesis of Fe(lll) complex of ligand L

92

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The solid state IR spectra of the original ligands and their complexes

are given in Table V. The infrared spectra of L and L® show a single

absorption band in 3396-3428 cm' region corresponding to free secondary

amino group. It is shifted to lower wavenumber by about 50 to 100 cm"

after coordination of the metal ions with nitrogen atoms of the ligands.^

Generally, the v(C=N) and v(C-N) absorb in the 1600-1650 cm"

and 1350-1450 cm" ranges, respectively, although in a highly conjugated

system the v(C=N) appears at lower wavenumber as has been found by

Patra and Goldberg^^ in such systems. However, these bands have been

found to be shifted to lower wavenumber in the complexes (Table V).

The magnetic moment values and electronic spectral bands are

given in Table(VI). Cobalt(ll) complexes have been widely studied. The

spectra of complexes [Co(L )Cl2] and [Co(L°)Cl2] have identical features,

indicating that the stereochemistry around the Co(ll) ion in solution are

alike. An octahedral Co(ll) species exhibits three transitions, but in practice

only two transitions have been observed.^^ We too, have observed two

absorption bands at 15,060 and 22,138 cm'"" for [Co(L )Cl2] and at 14,903

and 16,501 cm' for [Co(L )Cl2] corresponding to '*A2g(F)<-'*Tig(F) and

''Tig(P)<—' TigCF) transitions, respectively. These bands in the visible region

are consistent with spin allowed d-d transition for a six coordinate

octahedral Co(ll) ion. The observed magnetic moment values for the

[Co(L )Cl2] and [Co(L )Cl2] are 3.98 and 4.10 BM respectively, which is

98

consistent with the predicted high-spin value for an octahedral Co(ll)

complex with considerable orbital contribution to the overall magnetic

moment. '''°

It has been reported that the visible absorption spectra of the Fe(lll)

complexes exhibit bands in the region of 23,696 to 23,364 cm'"* which

correspond to a six coordinate Fe(lll) system.^^ In the present work, we

have observed for the [Fe(L )Cl2]CI complex, in the visible region, a single

absorption band at 22,676 cm' while for [Fe(L*)Cl2]CI complex a broad

band at 23,364 cm' corresponding to ''Tag^—%g transition has been

observed. The experimental magnetic moment in our case falls in the

range 5.89-5.97 BM (Table VI) which is very close to that calculated for a

high-spin d^ ion. The magnetic moment and UV-Vis spectra of the pale

yellow complexes of Fe(lll) with ligand L and L support an octahedral

geometry for the Fe{lll) ion.

The Cu(ll) complexes show one charge transfer band centered at

42,000 to 45,000 c m \ The band exhibited in the 14,000 to 15,000 cm'

region has been assigned to the T2g-«—Eg transition which is characteristic

of an octahedral copper(ll) ion. ^ It has been reported that the magnetic

moment of Cu(ll) complexes range between 1.73 to 2.20 BM. ^ In the

present case, the observed magnetic moments are 1.94 and 2.04 BM for

[Cu(L )Cl2] and [Cu(L )Cl2] respectively, which support an octahedral

geometry for Cu(ll) ion.

99

Three absorption bands have generally been observed for six

coordinate Mn{\\) complexes. ' We have also observed three bands at

30,959, 24,012 and 21,024 cm"'' for [Mn(L )Cl2] and at 31,112, 23,513 and

22,102 cm"'' for [Mn(L )Cl2] corresponding to the transitions '^Tig(P)^%g,

'*Eg(G)<- Aig and- '*T2g(G)<-%g, respectively, which is consistent with an

octahedral geometry for the Mn(ll) ion. The magnetic moment value of

Mn(l!) complexes with L and L° is lower than the calculated one which is

ascribed to an equilibrium between low and high-spin states of Mn(ll)ion.

H NMR spectra of [Cu(L )Cl2] and [Cu(L®)Cl2] were recorded in

DMSO-de and showed NH proton signal at 58.3. The signal at 67.1 for

[Cu(L )Cl2] complex is due to phenyl group. A broad band at about 51 to 52

indicates the presence of methylene protons present in the complex.

The thermogram of [Cu(L' )Cl2] can be divided into three major

regions showing weight loss of various components. The first step shows

the weight loss of about 16% in the temperature range 137 to 310 °C which

compares well with the calculated value of 15.7% corresponding to the

loss of two chlorides. The second step runs through 310 to 510 °C showing

a weight loss of neariy 39.6% which is equal to the benzil of organic

portion (39.2%). The third part of the weight loss curve corresponds to the

triethylenetetramine which comprises of 33% of the total weight compared

to 32.8% in the temperature range of 510 to 939 °C. In the end, the residue

left is copper metal (14%). ^

100

From the EPR spectra of the polycrystalline copper(ll) complexes at

room temperature, their g||, g i and axial symmetry parameter G = g||-2^x-2

have been calculated. The complexes did not show hyperfme structure at

room temperature. It may be attributed to strong dipolar and exchange

interaction between copper(ll) ions in the unit cell. The room temperature g

values of [Cu(L )Cl2] (g|| = 2.2377 and gi = 2.076765) and of [Cu(L )Cl2]

(g|| = 2.223 and gi = 2.083 ) suggest that dx%^ may be the ground state

for both of the complexes.



negligible while G < 4, indicates considerable exchange interaction in the

solid complexes. ^ For complexes [Cu(L )Cl2] and [Cu(L*)Cl2] the G values

are 3.096 and 2.69 respectively, which indicate a considerable exchange

interaction in the complexes.

101

REFERENCES

1. G. Mannaioni, R. Carpenedo, A. M. Pugliese, R. Corradetti and F. Moroni, Br. J. Pharmacol., 1998,125,175.

2. P. B. F. Bergqvist, R. Carpenedo, G. Apelqvist, F. Moroni and F. Bengtsson, Pharmacol. Toxicol. (Coperihagen), 1999, 85,138.

3. L. Somogyi, Bull. Chem. Soc. Jpn., 2001, 74, 873.

4. A. I. Vogel, Text Book of Quantitative Inorganic Analysis, Longmans Green, England, 1986, p507.


6. K. Nakamato, IR and Raman Spectra of Inorganic and Coordination Compounds, 4* Edition, John Wiley, New York, 1986.

7. B. N. Figgis, Introduction to Ligand Fields, Wiley Eastern Limited, 1966, p226.

8. C. J. Ballhausen, Introduction to Ligand Field Theory, Mc Graw Hill, New York, 1962, p253.

9. R. J. M. K. Gebbink, R. T. Jonas, C. R. Goldsmith and T. D. P. Stack, Inorg. Chem., 2002, 41, 4633.

10. F. A. Cotton, G. Wilkinson, C. A. Murillo and M. Bochmann, Advanced Inorganic Chemistry, 6** Edition, Wiley-interscience, New York, 1999, p821.

11. B. N. Figgis, Introduction to Ligand Fields, Wiley Eastem Limited, 1966, p220.

12. P. V. Bernhardt, E. G. Moore and M. J. Riley. Inorg. Chem., 2001, 40, 5799.

13. I. M. Procter, B. J. Hathaway and P. Nicholls, J. Chem. Soc. (A), 1968, 1678.

14. A. K. Mishra, P. Panwar, M. Chopra, R. K. Sharma and J. Chatal, New J. Chem., 2003, 27, 1054.

102

15. M. Maneiro, M. R. Bermejo, M. I. Fernandez, E. Gomez-Forneas, A. M. Gonzalez-Noya and A. M. Tyryshkin, New J. Chem., 2003, 27, 727.

16. G. C. Dismukes, Chem. Rev., 1996, 96, 2909.

17. P. G. Cozzi, L. S. Doici, A. Garelli, M. Montaiti, L. Prodi and N. Zaccheroni, New J. Chem., 2003, 27, 692.

18. Z. Liu and F. C. Anson, Inorg. Chem., 2000, 39, 274.

19. M. Munoz-Hernandez, M. L. l\/lcKee, T. S. Keizer, B. C. Yeanwood and D. A. Atwood, J. Chem. Soc. Dalton Trans., 2002, 410.

20. W. Leung, E. Y. Y. Chan, E. K. F. Chow, I. D. Williams and S. Peng. J. Chem. Soc. Dalton Trans., 1996,1229.

21. D. A. Atwood and M. J. Harvey, Chem. Rev., 2001,101, 37.

22. G. A. Morris, H. Zhou, C. L. Stern and S. T. Nguyen, Inorg. Chem., 2001,40,3222.

23. G. K. Patra and I. Goldberg, New J. Chem., 2003. 27, 1124.

24. A. Diebold, A. Elbouadili and K. S. Hagen, Inorg. Chem., 2000, 39, 3915.

25. R. A. Ghiladi, R. M. Kretzer, I. Guzei, A. L. Rheingold, Y. Neuhold, K. R. Hatwell, A. D. Zuberbuhler and K. D. Karlin, Inorg. Chem., 2001, 40, 5754.

26. F. A. Cotton, G. Wilkinson, C. A. Murillo and M. Bochmann, Advanced Inorganic Chemistry, 6* Edition, Wiley Interscience, 1999, p867.

27. A. B. P. Lever, Inorganic electronic spectroscopy, 2"* Edition, Elsevier Amsterdam, 1984.

28. S. Wang. Y. Hou, E. Wang, Y. Li, L. Xu, J. Peng, S. Liu and C. Hu, New J. Chem., 2003, 27, 1144.

103

CHAPTER V

SYNTHESIS AND CHARACTERIZATION OF

TRINUCLEAR COMPLEXES CONTAINING Cu(II) AND

Ti(IV)

SYNTHESIS AND CHARACTERIZATION OF TRINUCLEAR COMPLEXES CONTAINING Cu(ll) AND

Ti(IV)

The design of heteronuclear compartmental ligands capable of

binding two or more metal ions in close proximity are important for

providing functional heterometallic molecules. The growing interest in

electrochemical, magnetic, and spectroscopic studies of multimetallic

complexes is due to their importance in inorganic and bioinorganic

chemistry. ' They are universally available in nature as active sites in a

variety of metalloenzymes'* and play a significant role in catalysis. Many of

the complexes are also used as cocatalyst in metal-catalyzed

polymerization processes.^ Copper complexes with a variety of ligands

have been used in the binding and activation of CO, NO and O2 and as

models for metalloenzymes.^^ Recently, some dinuclear complexes have

been shown to exhibit catalytic activity for water oxidation to evolve

oxygen.^ Furthermore, they provide interesting cases for the study of

magnetic interactions ' ° and may also serve as models for some

metalloproteins. Multimetallic complexes containing cyclopentadienyl rings

have attracted increasing interest in the chemistry of metal complexes. ^

Currently, several efforts have been made to facilitate the synthesis of

planar, chiral cyclopentadienyl metal complexes in terms of their potential

as mediators or catalysts in asymmetric organic synthesis.^^ Planar, chiral

104

cyclopentadienyl metal complexes have advantages as catalysts since

coordination of a cyclopentadienyl ligand to a metal atom Is generally so

strong that there is almost no chance of ligand dissociation resulting in

racemization. In fact, planar, chiral cyclopentadienyl GroupIV metal

complexes were successfully used as catalysts in asymmetric organic

synthesis and polymerization.^^

In the current communication, the synthesis and characterization of

heterotrinuclear complexes of the type [Cu(ppn)2Cl2{Ti(Cp)2}2] (2) and

[Cu(en)2(N03)2{Ti(Cp)2}2l (4) are reported, where ppn-H2 =

1,3-diaminopropane, en-H2 = 1,2-diaminoethane and Cp =

cyclopentadienyl.

EXPERIMENTAL

1,3-Diaminopropane, 1,2-diaminoethane (Fluka), CuCb 2H2O

(Merck), Cu(N03)2 3H2O (Loba) and bis(cyclopentadienyl)titanium

dichloride (Aldrich) were used as received. THF was distilled and dried by

conventional methods.

Elemental analyses (C, H, N) were carried out with a 1106 Carlo

Erba analyzer. Chlorine was determined gravimetrically. IR spectra (4000-

450 cm' ) were recorded on a RXI FT-IR spectrometer as KBr discs. The

conductivity measurements were carried out with a CM-82T Elico

conductivity bridge in DMSO and MeOH. The electronic spectra were

105

recorded on a Cintra 5GBC spectrophotometer in DMSO and MeOH.

Magnetic susceptibility measurements were done with a 155 Allied


spectrum was recorded on a Bruker ACF 300 spectrometer at 300.12

MHz, using TMS as a reference in DMSO-de. EPR spectra of

polycrystalline samples were recorded on a RE-2X Jeol EPR spectrometer

fitted with 100 KHz field modulation.

Synthesis of [Cu(ppn-H2)2]Cl2 (1)

CuCIa 2H2O (10 mmol, 1.7 g) dissolved in methanol (25 mL) was

added to a methanolic solution (15 mL) of propanediamine (20 mmol. 1.64

mL) at room temperature, which immediately yielded a deep blue

crystalline compound. Since the yield was increased by cooling, the

contents were cooled to about 5 "C for 1h. It was then filtered, the residue

was washed with cold methanol and diethyl ether and dried over CaC^

under vacuo. Yield, 3.4 g (85%).

Synthesis of [Cu(ppn)2Cl2{Ti(Cp)2}2] (2)

A suspension of [Cu(ppn-H2)2]Cl2 (0.005 mole, 1.4 g) in THF (20 mL)

was treated with 20 mL of a THF solution of (Cp)2TiCl2 (0.01 mole, 2.48

g). A small amount of NH4CI was also added to facilitate the reaction. The

mixture was refluxed on a water bath for about 24 h, when a pale yellow

product was obtained. It was cooled to room temperature, filtered and the

106

residue was washed several times with ethanol and dried in vacuo. Yield,

1.7 g (55%).

Synthesis of [Cu(en<H2)2](N03)2 (3)

Cu(N03)2 3H2O (10 mmol, 2.41 g) dissolved in methanol (25 mL)

was added to a methanolic solution (15 mL) of ethylenediamine (20 mmol,

1.22 g) at room temperature, which immediately yielded a violet crystalline

compound. It was left at 5 °C for 1h which increased the yield. It was then

filtered, the residue was washed with cold methanol, ether and dried over

CaCl2 under vacuo. Yield, 2.5 g (90%).

Synthesis of [Cu(en)2(N03)2{Ti(Cp)2}2] (4)

A suspension of [Cu(en-H2)2](N03)2 (0.005 mole, 1.5 g) in THF (20

mL) was refluxed with (Cp)2TiCl2 (0.01 mole, 2.48 g) at 50-60 ""C in the

presence of a small amount of NH4CI, which yielded a green complex

under reflux. The resulting mixture containing complex (4) was cooled to

room temperature, filtered and the residue was washed several times with

ethanol and dried in vacuo. Yield, 2.0 g (62%).


Heterobimetallic complexes are of current interest due to their

unique physicochemical properties and functions arising from interaction or

interplay of dissimilar metal ions in close proximity^^ with each other.

107

New Cu(ll) and Ti(IV) heterotrinuclear complexes with multidentate

polyamine ligand linked by Ti atom on both sides were synthesized in

order to correlate structure and magnetic properties. The use of

mononuclear species such as [Cu(ppn-H2)2]Cl2 (1) and [Cu(en-H2)2](N03)2

(3) have been made as building blocks in which ppn-H2 and en-H2 act as a

bidentate ligand blocking all the coordination sites. The amino hydrogen of

polyamines can be easily replaced by the addition of (Cp)2TiCl2 resulting in

the formation of heterotrinuclear complexes. All the heterotrinuclear

complexes have been isolated in good yield and fully characterized. The

reaction of the complexes [Cu(ppn-H2)2lCl2 (1) and [Cu(en-H2)2](N03)2 (3)

with (Cp)2TiCl2 gives the heterotrinuclear chelates [Cu(ppn)2Cl2{Ti(Cp)2}2]

(2) and [Cu(en)2(N03)2{Ti(Cp)2}2l (4), respectively. The complexes are

formed by the replacement of amino hydrogen by Ti(IV) according to the

scheme in Fig. 1.

Molar conductance measurements of (1) and (3) in MeOH suggest

them to be 1:2 electrolytes while the heterotrinuclear chelates

[Cu{en)2(N03)2{Ti(Cp)2}2] (4) and [Cu(ppn)2Cl2{Ti(Cp)2}2] (2) are non-

electrolytes in DMSO.""*

The IR spectra (Table II) of primary amines show two N-H stretching

frequencies in the 3300-3500 cm' range which are shifted to lower

frequency on chelation. In compounds (1) and (3) these bands appear in

the 3200-3300 cm' range indicating chelation of Cu(ll) with ppn-H2 and

108

en-H2. However, in compounds (2) and (4) a single absorption band

appears at 3013 and 3232 cm' which is attributed to v(N-H) of the

coordinated secondary amine, ^ as one of the hydrogen from en-H2 or ppn-

Hawas replaced by Ti(IV).

CuCb.2H20 + 2 H2N NH2

H2N NH2

H2N NH2

-4HC1

Cb

2(Cp)2TiCl2

• Ti( ^Cu Ti

Fig. 1. Synthesis of trinuclear complex (2)

109

Cu(N03)2-3H20 + H2N NH2

1 \ ^

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(N03)2

2(Cp)2TiCl2

NO3 H

Cp, N

TiC Cu Ti

H 1/

N Cp

Cp N

H

N Cp

NO 3

Fig. 2. Synthesis of trinudear complex (4)

110

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Since only one absorption band at 1387 cm" has been observed for

[Cu(en)2](N03)2, it is suggested tliat the NOa" group is not bonded to metal

in this case. In the case of [Cu(en)2(N03)2{Ti(Cp)2}2] (4), four bands

assigned to the NOa" absorption frequency have been observed at 1510,

1384, 1041 and 815 cm' (Table II) which indicate the coordination of NO3"

to metal ion. ^ It is also supported by v(Cu-O) at 487 cm' which is absent

in compound (3).

It is difficult to distinguish between uni- and bidentate nitrate ligands

because they both have the same symmetry. However, from a study of

metal nitrates^^ it has been shown that the difference between symmetric

and asymmetric (A(as-s) NO3) stretch is small (150-250) when NOs" in

unidentate while for a bidentate NO3" group bonded to a metal ion, the

difference of asymmetric minus symmetric frequencies (A(as-s)) is very

large^^ (300-400 cm" ). Recently, Fujisawa^^ et al. have studied the type of

nitrate binding mode depending upon the separation between the Vas(N03)

and Vs(N03) frequencies. They further corroborated their results from X-ray

crystal structures of nitrato copper(ll) complexes of tris(pyrazolyl)borate. In

our case, in the complex (4) A(as-s) is of the order of 126 cm' compared to

300-400 cm" for a bidentate N03~ group which is suggestive of a

unidentate NOs" group which renders Cu(ll) octahedral although distortion

may occur.

114

The electronic spectra of complexes (1) and (3) were recorded in

MeOH and those of (2) and (4) in DMSO (Table III). On the basis of

molecular orbital calculations three to four absorption bands have been

predicted in the case of Cu(ll) complexes with square-planar geometry.^"

However, in most cases, Cu(ll) complexes exhibit only one d-d band in the

15,000 to 18,000 cm" region. ' ^ De Rose and coworkers^^ have shown,

in a study of a Cu(ll) complex with peptide, the appearance of only one d-d

band at 550 nm besides charge transfer. We have also observed only one

d-d band in the case of complex (1) and (3) in the above range which is

consistent with a square-planar geometry of Cu(ll).

The bis-cyclopentadienyltitanium derivative of [Cu(ppn-H2)2]Cl2 i.e.

(2) shows a charge transfer band at 306 nm and a broad d-d absorption

band at 898 nm, which is entirely different from that of the complex (1).

Such absorption bands are generally observed for octahedral Cu(ll)

complexes. '* The UV-Vis spectrum of (4) displays an absorption band at

325 nm which is assigned to the NO3" -> Cu(ll) charge transfer. ^ In the

ligand field region, the d-d band has been observed at 647 nm which is

consistent with an octahedral geometry for the Cu(ll) complex. Stephens^^

has also reported a distorted octahedral geometry for the Cu(ll) complex

with diethylenetriamine.

Magnetic moment values of (4) and (2) are very close to those

calculated for one unpaired electron (Table III). Electronic absorption

115

spectra and magnetic moments are suggestive of an octahedral geometry

around Cu(ll) although distortion of the octahedron may occur due to the

Jahn-Teller effect. Thus, on moving from mononuclear to the trinuclear

complexes (2), (4) there is a shift in d-d transition which is ascribed to the

change in coordination number and environment around the Cu(ll) centre.

The EPR spectra of the polycrystalline copper(ll) complexes at room

temperature showed a strong signal and their g||, gi and axial symmetry

parameter (G = g||-2^gi-2) were calculated. Complexes did not show

hyperfine structure at room temperature. This may be attributed to strong

dipolar and exchange interaction between copper(ll) ions in the unit cell.

The room temperature g values of (4) (g|| = 2.231 and gi = 2.065) and (3)

(gil =2.13 and gi = 2.07) suggest that dx%^ may be the ground state for

both of the complexes. Complex (1), (g|| = 2.22 and gx = 1.90) also

indicates that 6^.^ may be the ground state, but for the complex (2)

g|| = 2.056 and gi = 2.18 suggest that d / may be the ground state. The

Cu(ll) ion may get strongly coordinated to CI" which may be responsible for

the change of the character of the ground state resulting in a dz state. ^




solid complexes. '' For complexes (3) and (4) the G values are 1.857 and

116

3.55, respectively, which indicate a considerable exchange interaction in

the complexes.

H NMR spectrum of complex (4) was recorded in DMSO-de and

showed signals at 58.29 (m) which is assigned to N-H protons, inferring

replacement of one of the two NH2 protons and simultaneous coordination

of nitrogen atom to Ti(IV). The signal at 87.2 (s) is due to cyclopentadienyl

group. A multiplet at 52.8 (m) indicates the presence of methylene protons,

which are coupled both by NH and adjacent methylene protons.

117

REFERENCES

1. S. G. Telfer, B. Bocquet and A. F. Williams, Inorg. Chem., 2001, 40, 4818.

2. M. Kodera, Y. Taniike, M. Itoh, Y. Tanahashi, H. Shimakoshi, K. Kano, S. Hirota, S. lijima, M. Ohba and H. Okawa, Inorg. Chem., 2001,40,4821.

3. K. Herbst, M. Monari and M. Brorson, Inorg. Chem., 2001, 40, 2979.

4. P. J. Hart, M. M. Balbirnie, N. L. Ogihara, A. M. Nersissian, M. S. Weiss, J. S. Valentine and D. Eisenberg, Biochemistry, 1999, 38, 2167.

5. E. Y. Chen and T. J. Marks, Chem. Rev., 2000,100,1391.

6. L. M. Berreau, J. A. Halfen, V. G. Young and W. B. Tolman, Inorg. C/7/m.Acfa., 2000, 297, 115.

7. J. A. Halfen, B. A. Jazdzewski, S. Mahapatra, L. M. Berreau, E. C. Wilkinson, L. Que and W. B. Tolman, J. Am. Chem. Soc, 1997, 119, 8217.

8. K. Nagoshi, M. Yagi and M. Kaneko, Bull. Chem. Soc. Jpn., 2000, 73,2193.

9. J. Tercero, C. Diaz, M. S. E. Fallah, J. Ribas, X. Solans, M. A. Maestro and J. Mahia, Inorg. Chem., 2001, 40, 3077.

10. E. Gao, J. Tang, D. Liao, Z. Jiang, S. Yan and G. Wang, Inorg. C/7em., 2001, 40, 3134.

11. G. S. Hair, R. A. Jones, A. H. Cowley and V. Lynch, Inorg. Chem., 2001,40, 1014.

12. D. B. Grotjahn, H. C. Lo, J. Dinoso, C. D. Adkins, C. Li, S. P. Nolan and J. L. Hubbard, Inorg. Chem., 2000, 39, 2493.

13. Y. Nakamura, M. Yonemura, K. Arimura, N. Usuki, M. Ohba and H. Okawa, Inorg. Chem., 2001, 40, 3739.

118


15. M. P. Suh and S. Kang, Inorg. Chem., 1988, 27, 2544.

16. M. R. Rosenthal, J. Chem. Educ, 1973, 50, 331.

17. B. 0. Field and C. J. Hardy, J. Chem. Soc, 1964, 4428.

18. K. Nakamato, IR and Raman Spectra of Inorganic and Coordination Compounds, 4th Edition, New York, John Wiley, 1986.

19. K. Fujisawa, T. Kobayashi, K. Fujita, N. Kitajima, Y. Moro-oka, Y. Miyashita, Y. Yamada and K. Okamoto, Bull. Chem. Soc. Jpn., 2000, 73, 1797.

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26. F. A. Cotton, G. Wilkinson, C. A. Murillo and M. Bochmann Advanced Inorganic Chemistry, 6* Edition, Wiley Interscience, 1999, p865.


119

CHAPTER VI

SYNTHESIS AND CHARACTERIZATION OF METAL

COMPLEXES CONTAINING DITHIOCARBAMATE AND

POLYPYRIDINE

SYNTHESIS AND CHARACTERIZATION OF METAL COMPLEXES CONTAINING DITHIOCARBAMATE AND

POLYPYRIDINE

Transition metal diimine dithiolate complexes have been found to

have a number of interesting electronic structural properties that have

served to stimulate interest in these systems.'' It has been reported that

complexes containing 1,1-dithiolate ligands exhibit solvatochromic bands

at higher energies than analogous 1,2-dithiolate systems.^ Further support

has come from promising results concerning the use of metal diimine

chromophores in solar energy conversion, photocatalysis and

photolumlnescence probes of biological systems. Synthetic strategies are

aimed at preparing complexes having a high degree of stability and having

excited state properties that can be controlled by systematic variation in

molecular structure.

1,10-phenanthroline and 2,2'-bipyridine are the ligand of choice as

they form stable complexes with a wide range of metal ions and are

relatively easily functionalized.^ 1,10-phenanthroline has always attracted

interest because it has a rigid structure imposed by the central ring, such

that the two nitrogen atoms are always in juxtaposition, for instance, in

2,2'-bipyridine systems, free rotation about the linking bond allows the two

nitrogens to separate. The entropic advantage of phenanthroline means

that formation of complexes with metal ions is faster."*

120

In view of the various properties of bipyridine and phenanthroline we

thought it appropriate to study a complex containing both S and N ligands

vis a vis a complex containing dithiocarbamate (dtc) and bipyridine (bpy) or

phenanthroline (phen), One of the most striking features of

dithiocarbamate group is its high nucleophilicity which leads to a large

number of derivatives. Although the reports on metal dtc are extensive the

studies of transition metal complexes containing both dtc and polypyridine

ligand are few in number.^ Such mixed ligand complexes have been used

as non-chromophoric chelating ligands to tune sensitizer absorption

properties and efficiently sensitize Ti02/

We report here the synthesis and characterization of mixed ligand

complexes of the type [M(dtc)2(bpy)] and [M(dtc)2{phen)] where M = Mn(ll),

Co(ll), Ni(ll), Cu(ll)andZn(ll).

EXPERIMENTAL

2,2'-Bipyridyl, 1,10-Phenanthroline, sodium salt of N,N'-diethyl

dithiocarbamate (Merck) and hydrated metal chlorides (BDH) were used as

received. Elemental analyses (C, H, N) were carried out with a Carbo Erba

EA-1108 analyzer. IR spectra (4000-400 cm""") were recorded on a RXI FT-

IR spectrometer as KBr discs. The conductivity measurements were

carried out with CM-82T Elico conductivity bridge in nitrobenzene. The

electronic spectra were recorded on a Cintra 5GBC spectrophotometer in

121

CHCI3. Magnetic susceptibility measurements were done with a 155 Allied


spectra were recorded on a Brucker Ac 250 spectrometer at 250 MHz,

using TMS as a reference in CDCI3. EPR spectra of copper complexes

were recorded on a RE-2X Jeol EPR, spectrometer fitted with 100 KHz

field modulation.

Synthesis of fCu(bpy)Cy

To a cold methanolic solution (50 mL) of 2,2'-bipyridine (1.56 g,

10 mmol) hydrated CuCIa dissolved in 50 mL MeOH (10 mmol, 1.7 g) was

slowly added, with stirring, which afforded brisk precipitation of light green

complex. It was filtered, the residue was washed with cold methanol and

dried in vacuo. Yield, 2.7 g (92%). [Zn(bpy)Cl2] was also synthesized by

the above method. Yield, 2.5 g (86%).

Synthesis of [Ni(bpy)Cl2]

Hydrated NiCl2 (10 mmol, 2.37 g) in 100 mL methanol was slowly

added to a methanolic solution (50 mL) of 2,2'-bipyridine (1.56 g,

10 mmol). The mixture was stirred for half an hour at room temperature. It

was then reduced to half by evaporation and was left for three to four days

which yielded bluish green precipitate. It was filtered, the residue was

washed with methanol and ether and dried in vacuo. Yield, 2.37 g (83%),

122

[Co(bpy)Cl2] Yield, 2.08 g (73%) and [Mn(bpy)Cl2] Yield, 2.0 g (71%) were

also synthesized by the above procedure.

Synthesis of [Cu(bpy)(dtc)2]

A methanolic solution (100 mL) of sodium salt of

N,N'-diethyldithiocarbamate (4.5 g, 20 mmol) was added to a suspension

of [Cu(bpy)Cl2] (2.9 g, 10 mmol) in the same solvent. The mixture was then

stirred for 2 h at room temperature which afforded yellowish green

precipitate. It was filtered and was extracted repeatedly with chloroform.

The extract was reduced to half and reprecipitated from ether as yellowish

green complex. It was then dried in vacuo. Yield, 3.24 g (63%)

[Zn(bpy)(dtc)2] was also synthesized in the same way. Yield, 3.15 g (61%).

Synthesis of [Nl(bpy)(dtc)2]

To a methanolic solution (100 mL) of [Ni(bpy)Cl2] (10 mmol, 2.85 g)

sodium salt of N,N'-diethyldithiocarbamate (4.5 g, 20 mmol) dissolved in

100 mL methanol was added and the mixture was stirred at room

temperature for 2 h, which yielded a light green precipitate. The precipitate

was extracted repeatedly with chloroform. It was reduced to half and

reprecipitated from diethyl ether as green complex. It was filtered and dried

in vacuo. Yield, 4.5 g (89%). [Co(bpy)(dtc)2] {Yield, 4.38 g (86%} and

[Mn(bpy)(dtc)2] complexes {Yield, 4.1 g (81%)} were also synthesized by

the above procedure.

123

Synthesis of [Cu(phen)Cl2]

To a cold methanolic solution (100 mL) of 1,10-phenanthroline

(1.98 g, 10 mmol) hydrated CUCI2 (10 mmol, 1.7 g) dissolved in 50 mL

methanol was slowly added at room temperature which afforded brisk

precipitation of a green complex. It was filtered, the residue was washed

with cold methanol and dried in vacuo. Yield, 2.92 g (93%). [Zn(phen)Cl2]

was also synthesized by the above procedure. Yield, 2.9 g (92%).

Synthesis of [Ni(phen)Cl2]

Hydrated NiCl2 (10 mmol, 2.37 g) in 50 mL methanol was slowly

added to a methanolic solution (50 mL) of 1,10-phenanthroline (1.98 g,

10 mmol). The mixture was stirred for half an hour at room temperature

and reduced to half by evaporation. It was left for three to four days which

yielded bluish green precipitate. It was filtered, the residue was washed

with methanol and ether and dried in vacuo. Yield, 2.72 g (88%).

[Co(phen)Cl2] {Yield, 2.35 g (76%)} and [Mn(phen)Cl2] {Yield, 2.23 g

(73%)} were synthesized by the above procedure.

Synthesis of [Cu(phen)(dtc)2]

A methanolic solution (100 mL) of sodium salt of

N,N'-diethyldithiocarbamate (4.5 g, 20 mmol) was added to a suspension

of [Cu(phen)Cl2] (3.14 g, 10 mmol) in the same solvent. The mixture was

then stirred for 2 h at room temperature which afforded yellowish green

124

precipitate. The precipitate thus obtained was extracted repeatedly with

chloroform. The extract was concentrated to a small volume and

precipitated from ether. It was then dried in vacuo. Yield, 3.4 g (63%).

[Zn(phen)(dtc)2] was also synthesized by the above procedure. Yield, 3.7 g

(69%).

Synthesis of [Ni(phen)(cltc)2]

To a methanolic solution (100 mL) of [Ni(phen)Cl2] (10 mmol, 3.09 g)

sodium salt of N,N'- diethyldithiocarbamate (4.5 g, 20 mmol) dissolved in

50 mL methanol was added and the mixture was stirred at room

temperature for 2 h, which yielded light green precipitate. It was extracted

repeatedly with chloroform and the solution was reduced to half. It was

reprecipitated with ether as yellowish green precipitate. It was filtered and

dried in vacuo. Yield 4.86 g (91%). [Co(phen)(dtc)2] {Yield. 4.64 g (87%)}

and [Mn(phen)(dtc)2] complexes {Yield, 4.24 g (80%).} were synthesized

by the above procedure.


The reaction of the complexes [M(bpy)Cl2] and [M(phen)Cl2] with

sodium salt of N.N'-diethyldithiocarbamate gives the mixed chelates

[M(bpy)(dtc)2l and [M(phen)(dtc)2], respectively where M = Mn(ll), Co(ll),

Ni(ll), Cu(ll) and Zn(ll). They are formed by the replacement of two

chlorine atoms by diethyldithiocarbamate according to the scheme, in

125

Fig. 1. The molar conductance of the complexes measured in nitrobenzene

(7-18 ohm" cm^mol" ) Indicated that they are non-electrolytes.^

Table II lists the characteristic infrared frequencies for the transition

metal complexes. Attempt has been made to deduce the denticity of the

dtc using v(C-N) and v(C-S) regions of the spectra. According to the

criterion of Brinkhoff and Grotens^°, the C-S stretching frequency region

(950-1050 cm" ) is highly diagnostic of the nature of the dtc vis a vis

unidentate or bidentate ligand. The IR spectra of all of the complexes

under consideration exhibited a single strong absorption band v(C-S) in

989-998 cm' range which is indicative of bidentate nature of the dtc group.

The important IR bands arise from v(CS2)asym at ~ 1138cm' and v(CS2)sym

at ~ 994 cm" in the metal complexes. For a symmetric bonding of CS2

group the difference between symmetric and asymmetric CS2 stretching

frequency in metal complexes is always higher (150 cm' ) than the

corresponding difference between these frequencies in R2NCS2Na while

for anisobidentate this difference should be less than 150 cm'\^^ In our

case, the difference between asymmetric and symmetric CS2 stretching

frequency is less than that in the free salt. It is suggested that the metal ion

is coordinated in anisobidentate fashion.

The thioureide band appeared in 1430-1450 cm'"* range which is

Intermediate between a v(C=N) band (1690-1640 cm" ) and a v(C-N) band

126

(1360-1250 cm" ) indicating a partial double bond character between

carbon and nitrogen.

In the free bpy or phen molecule, strong interactions between C=C

and C=N give rise to two groups of doublets^^ which undergo rennarkable

changes after coordination. They are shifted to lower wave number after

complexation.

The UV spectra of all of the complexes show five absorption bands

due to the NCS2 and polypyridyl chromophore.^^^^ These absorptions are

indicated as band I, II, III, IV and V. Band I (near 35,714 cm" ) is assigned

to an intramolecular charge transfer in the ligand, i.e. a JT*- IT transition

located mainly in the N-C-S group. Band II (33,333-31,250 cm' ) is

attributed to a TTV TT transition of the S-C-S group. Band III

(26,315-25,000 cm' ) is a low intensity band and may be assigned either to

a TTV n electronic transition located on the sulfur atom or to M<-L charge

transfer. The spectra also contain characteristic vibronic structure of the

diimine centered LL transition, ^(TTVR) lying between 30,303-27,027 cm'

region. A common band appears around 40,000 cm'"* in each complex. It

has been assigned to a higher energy spin allowed LL transition TT2 -n

centered on the bipyridyl or phenanthroline ligand.

The visible absorption of copper(ll) complexes display broad,

unsymmetrical bands with two discernible adjacent maxima between

19,513-19,267 cm' and 17,761-17,513 cm" for [Cu(bpy)(dtc)2] and

127

o

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Fig. 1. Synthesis of metal complexes containing bipyridine and N,N'-diethyl dithiocarbamate

128

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Fig.2. Synthesis of metal complexes containing phenanthroline and N,N'-diethyl dithiocarbamate

129

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[Cu(phen)(cltc)2] respectively. The splitting of the band is either due to

Jahn-Teller distortion, spin-orbit coupling or lowering of symmetry and

hence have been considered belonging to the transition, T2g (split) <-

^Eg.'' It is difficult to predict solution structure of the Cu(ll) complexes from

electronic spectroscopy alone because of a wide range of possible

geometrical distortions and the typically poor resolution of absorption

bands. ^ In order to examine if the [Cu(phen)(dtc)2] complex in different

solvents undergoes solvatochromic shift the complex was dissolved in a

variety of polar solvents such as DMSO, DMF, THF,CHCl3, CH2CI2,

C6H5NO2 and acetone and their UV-Vis spectra were recorded. Since the

spectra do not exhibit any variation in absorption pattern as a function of

solvent it is suggested that binding of the solvent at Cu(ll) ion does not

occur. ^ It means that geometry of Cu(ll) ion does not change in solution.

However, the observed magnetic moment value is in the range between

1.93 - 2.01 BM which corresponds to an octahedral structure for the Cu(ll)

ion.

Octahedral Ni(ll) complex is known to exhibit three spin allowed

electronic transitions within the visible region.""* In the case of

the [Ni(bpy)(dtc)2], two absorption bands at 22,727 cm'^vi) and

15,873 cm'^vs) have been observed while for the [Ni(phen)(dtc)2] complex,

these bands appear at 22,727 cm'^vi) and 15,920 cm"''(v3) range. The vi

135

is due to one of the spin allowed electronic transitions in the visible region

^Tig(P) <— ^A2g(F). Careful inspection of the spectra reveals the presence of

a shoulder at 20,920 cm"''(v2). The position of the middle band (V2) has

been attributed to ^Tig(F) *- A2g transition. Relatively, a lower energy band

V3 has been ascribed to T2g(F) *- A2g(F) transition. The ligand field

parameters viz 10Dq, B(Racah parameter), p (Nephelauxetic ratio) are

almost identical for [Ni(dtc)2(bpy)] and [Ni(dtc)2(phen)]. Values of ligand

field parameters reflect that the M-L bond is sufficiently strong, which in

turn suggest effective overlapping of metal orbitals with those of the ligand.

The compounds are paramagnetic with a room temperature magnetic

moment of 3.6 - 3.9 BM which is consistent with an S = 1 ground state in

an octahedral field.

Cobalt(ll) complexes have been widely studied. The spectra of

[Co(bpy)(dtc)2] and [Co(phen)(dtc)2] have identical features, indicating that

the stereochemistry around the Co(ll) ion in solution are alike. They show

absorptions at about 23,148 cm"\ 15,550 cm'"" and 11,330 cm'"* (Table III).

The low frequency band at about 11,330 cm""" assigned to the

'*T2g(F) <- '*Tig(F) transition is characteristic of a distorted octahedral

geometry for Co(ll) ion."" In addition, a second band assigned to the

' TigCP) ^ ''Tig(F) is seen in the visible region at 23,148 cm'\ while the

band at about 15,576 cm" corresponds to the transition '*A2g <- '*Tig(F)

showing octahedral environment around Co(ll). The observed magnetic

136

moment values for the [Co(bpy)(dtc)2] and [Co(phen)(dtc)2] are 4.18 and

4.21 BM respectively, which are within the range of high-spin octahedral

Co(ll) complex with considerable orbital contribution to the overall

magnetic moment. °" ^

The electronic spectra of Mn(ll) chelates exhibit bands in the region

20,661 - 20,747 cm ^ and 17,513 cm-\ assigned to the ''T2g(G) ^ %g and

' TigCG) •«— ^Aig transitions respectively, correspond to a typical octahedral

Mn(ll) ion. ^

The H NMR spectra of the compounds [Zn(phen)(dtc)2] and

[Zn(bpy)(dtc)2] were recorded in deuterated chloroform solution. It

exhibited the expected signal for ethyl protons of the dithiocarbamate^^ and

protons of phenanthroline and bipyridine ligands. ^ The methylene protons

(8H) gave quadrate between 53.6-3.9 (J = 7-8). Since the methyl protons

(12H) couple with the equivalent neighbouring methylene protons they

appear as a triplet at higher field between 51.26-1.3.

The resonances due to the phenanthroline protons were found as a

multiplet between 59.6-7.8. The protons adjacent to the nitrogen atoms

(2H) appear downfield as a doublet at 59.56. The two vinylic type protons

(2H) of the phenanthroline appear as a singlet at 57.90. The m-proton (2H)

appear as a double doublet at 57.9 (J = 3-4). Furthermore, the p-proton

appears as doublet at 58.4.

137

Four sets of proton signals of bipyridine were observed in

[Zn(bpy)(dtc)2] indicating their non equivalence. The protons adjacent to

the nitrogen atom (2H) appear downfield as a doublet at 59.26 while the

m-protons (2H) appear as double doublet at 57.87 (J = 4.5-5). The

p-proton (2H), however, appear as double doublet at 67.69. The remaining

(2H) protons of bipyridine appear as doublet at 57.51.

These values correspond to the anticipated structure of the

complexes. (Fig. 1,2)

The EPR spectra of the copper(ll) complexes at room temperature

showed a strong signal and their g||, gx and axial symmetry parameter

(G = Q\\-2/Qi-2) have been calculated. No complex shows hyperfine

structure at room temperature. This may be attributed to strong dipolar and

exchange interaction between copper(ll) ions in the unit cell. The room

temperature g values of [Cu(bpy)Cl2] (g|| = 2.2399 and gi = 2.0783) and

[Cu(phen)Cl2] (g|| = 2.2377 and gi = 2.0738) suggest that dx%^ may be the

ground state for both of the complexes. ^ Complex [Cu(phen)(dtc)2],

(g|l = 2.0866 and gi = 2.0548) also indicates that dx%^ may be the ground

state, but for the complex [Cu(bpy)(dtc)2] a strong single band with

g = 2.0599 has been observed.

It has been reported that low g|| values are common for six

coordinate Cu(ll) complexes with ligands containing N and S donor sets. ^

138

We, too, have observed very low g|| values for [Cu(phen)(dtc)2] complex,

which is consistent with a six coordinate Cu(ll) complex with N and S

donor sets. The most remarkable feature is that the g|| values for

[Cu(bpy)Cl2] and [Cu(phen)Cl2] is 2.2399 and 2.2377, respectively, which

are higher as compared to those for [Cu(bpy)(dtc)2] (g = 2.0599) and

[Cu(phen)(dtc)2] (g|| = 2.0866) complexes. Such high values are known for

complexes with ligands containing hard donors like oxygen and nitrogen,

but rarely with sulfur donor ligands.




solid complexes. ^ For complexes [Cu(bpy)Cl2], [Cu(phen)Cl2] and

[Cu(phen)(dtc)2] the G values are 3.06, 3.22 and 1.58 respectively, which

indicate a considerable exchange interaction in the complexes.

139

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141

MARCEL DEKKER, INC.

Reprint Program

a^MAi»soN AVENUE • NEW Ycauc NY icx>i6

SYNTHESIS AND REACTTVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY

Vol. 33, No. 10, pp. 1835-1855, 2003

Novel N4 Macrocycles and Their Transition Metal Chelates

K. S. Siddiqi,^'* N. Nishat,^ and Fouzia Rafat*

^Department of Chemistry, Aligarh Muslim University, Aligarh, India ^Department of Chemistry, Jamia Millia Islamia, New Delhi, India

ABSTRACT

Four novel N4-type macrocyclic chelating agents L \ L^, L^, L!^ with pendant groups and their metal chelates with some transition metal ions have been synthesized. Electrical conductance of the Cr(in) and Fe(in) chelates indicated them to be 1:1 electrolytes whilst those of divalent metal ions are non-electrolytes in DMSO. Spectroscopic evidence suggests that all of the complexes are six-coordinate and the pendant groups are not involved in coordination.

*Correspondence: K. S. Siddiqi, Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India; E-mail: [email protected].

1835

DOI: 10.1081/SIM-120026552 0094-5714 (Print); 1532-2440 (Online) Copyright © 2(X)3 by Marcel Dekker, Inc. www.dekker.com


http://www.dekker.com

1836 Siddiqi, Nishat, and Rafat

INTRODUCTION

The coordination properties of macrocycle bearing pendant groups have attracted great deal of attention. '""^^ More recently, the crystal and molecular structure of [3-(4-pyridimumcarbonyl)-1,3,5,8,12,-pentaazacyclotetra-decane]-nickel(II) was described^ ^ in which pyridine acts as pendant group. A metallocyclam subunit has been appended to pyridine through a metal template procedure which involves the condensation of amides of 3- and 4-pyridine carboxylic acid with formaldehyde and the nickel(II) complex with the open-chain tetraamine. These metallocyclam units act as building blocks of supramolecular system and act as two-electron redox systems. In the recent past, a 36-membered macrocycle with four ethylenediamine entities has been reported. ^

The synthesis of transition metal complexes with macrocycles containing a variety of functional groups on the periphery has been reported. ^^ These groups have been termed superstructures. Such compounds are of particular importance in view of their use in the treatment of malignant tumors. ^ Increasing interest has been shown in the design of new macrocycles with predetermined guest complexation. ' ^^ In view of these observations it was considered worthwhile to investigate, in detail, the synthesis of four tetradentate macrocycles and their chelates with transition metal ions.


A mixture of 4-aminoantipyrine, acetylacetone and 1,3-diaminopropane or 1,6-diaminohexane was refluxed. It was cooled to zero °C and an excess of dilute HCl was added to cause precipitation of L and L^ as shown in Figure 1.

For the synthesis of L and L"*, a mixture of 4-aminoantipyrine, 1,3-diaminopropane or ethylenediamine was refluxed for 20 h. It was cooled to zero °C and precipitated with dilute HCl. This product was dissolved in ethanol and refluxed with benzoylacetic acid. Addition of dilute HCl afforded the ligands L^ and V^ (Figure 2).

Metal complexes were synthesized directly by the addition of hydrated metal chloride solutions to the ligand solution in the same solvent. Since the yield of the complexes was too poor (10 to 15%), the in situ method was employed. In this method the ligand was not isolated. The metal chloride was added to the solution of the ligand under preparation.

Elemental analyses of the complexes correspond to the compositions MLCI2 and M'LCIs where M = Mn(n), Co(n), Ni(II), Cu(II) and Zn(n) and

Novel N4 Macrocycles 1837

H3C NH2

H3C' ^-Ao 0 o

H3C / ' ' ^ C H / \ CH3

EtOH -2H2O

H3C. CH3

H j C ^ ^ ^ N N

H3C'N^, A o 0^^-^^CHi

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H2N NH2

Ice EtOH

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H3C. CH3

H3C ^ ^ N N ^ CH3

HjC"^ Y N N ^ N " ^CH3

n = 0 for L'

andn = 3 forL

Figure 1. Synthesis of ligands L* and L .

M' = Cr(III) and Fe(in). The molar conductances measured in DMSO (15-42 ohm"' cm^ mole"') indicated that the divalent metal complexes are non electrolytes^'^^ while those of M(in) ions are 1:1 electrolytes (Table 1).

IR Spectra

It has been observed by many workers^''"'^^ that in Schiff base macrocycUc complexes the C = N stretching frequency appears in the 1620-1660 cm"' region. A comparison of the IR spectra of the free macrocycles


+ H2N NH2

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H^ ^COOH H5C6\ ^ X L /C6H5

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n = 0 for L' and n = 1 for L

Figure 2. Synthesis of ligands L^ and L'*.

with those of their complexes indicated a substantial shift in v(C=N) and v(C-N) (Table 2). The presence of v(NH) in L^ and L'^ and their complexes has been supported by the appearance of a band in the 3080-3230 cm~^ region. It is interesting to note that v(COOH) consistently appears at 1430 cm~' in both the free (L^ and L"*) and chelated macrocycles which implies that the pendant group is not coordinated in any case although macrocycles having pendant donor groups that are capable of coordinating with the central metal ions are knownJ ^ Some 'scorpiand' type molecules are also reported having H2N-CH2 'tails' to a tetraamine macrocycle. '

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o o < s o o e N a \ r ~ 0 ' - > n v D O ' *

fn 00 — fs . en op • >r) 'J rn o\ cs 0^ fo ra r-* -T o\ (O CS — (N "

• 00 r- Ov 00 00 m 00 o\ r o ~ • — -01 -^ p, o^ ro Tt' pvf ri o r- Tf ,

— cs (N -- m en -H

o ON

r4

00

I 00

u s ^ P-.

1 u

1 z

i u

1 N

00


The far IR spectra of the complexes show intense halogen-sensitive absorptions in the 255-300 cm~ region. The bands in the 320-390 cm~ range are assigned to v(M-N) vibrations. A band at 1070 cm"' in all the ligands and complexes is assigned to v(N-N) in pyrazole.

Electronic Spectra and Magnetic Moments

The magnetic moment values and electronic spectral bands are given in Table 3. Three bands characteristic of octahedral nickel(n) ion in a high-spin state are anticipated. In the present case the bands observed have been assigned to 'TjgCP) 'A2g(F), 'Tig(F)^3A2g(F) and 'Tig(P)^'A2g(F) transitions. '"*^ The electronic spectral bands and the relatively low magnetic moments suggest a distorted octahedral geometry for nickel(II) ion.

In all of the cobalt(II) complexes three bands have been observed. The magnetic moment value of CoCH) complexes with L \ L and L"* is very low which is probably due to an equiUbrium between low and high spin states of Co(II). However, the electronic bands and the pink colour of the complexes are consistent with an octahedral envirormient around cobalt(n) ion (Figure 3)..

The observed magnetic moment values for chromium(III) complexes are close to that calculated for a d ion, corresponding to an octahedral geometry (Figure 4).

The magnetic moment for all of the manganese(n) complexes ranges between 5.98-6.12 B.M. which correspond to a high-spin octahedral structure for the metal ion. ' ^

The iron(III) complexes exhibit three bands. In the high-spin complexes the theoretical magnetic moment value is 5.91 B.M. We have obtained for these complexes values in the range for a high-spin octahedral geometry. '* ^

The copper(n) complexes show one or two charge transfer bands. The band exhibited in the 11,235-13,157 cm"' region is assigned to the 2g —^Eg transition which is characteristic of an octahedral copper(II) ion.

The magnetic moment value also supports the above geometry.

EXPERIMENTAL

4-Aminoantipyrine, ethylenediamine, 1,3-diaminopropane, 1.6-diami-nohexane (Koch Light) ethyl acetoacetate (S.D. Fine chemicals), acetylacz-etone, benzoylchloride, and hydrated metal chlorides (BDH) were used as received. Benzoylacetic acid was synthesized and recrystallized by the literature method.' ' ^ Elemental analyses were carried out with a Carlo Erba 1106 analyser. The metals were determined by complexometric titration ' ^


using EDTA and CI was determined gravimetricallyJ^^^ The IR spectra (4000-200 cm~^) were recorded on a 621 Perkin-Elmer grating spectrometer as KBr disc. The electronic spectra were recorded in DMSO on a Carl-Zeiss VSU2P spectrophotometer. Magnetic susceptibility measurements were done with an AlUed Research model 155 vibrating sample magnetometer and the molar conductances were measured at room temperature using a Systronics 321 conductivity bridge.

L ' or L (prepared in situ)

MCI,

n = OforL' n = 3forL^

M = Mn(II), Co(II), " ^ Ni (II), Cu(II) and Zn(II)

N-" CH3

L or L'* (prepared in situ)

MCI,

n = 0 for L' n=lforL'*

H->C

HaC^ \

H COOH

T pCHzCOOH ,N CI N r "

\ I MT

M = Mn(n), Co(II), Ni (H), Cuai) and Zn(II)

Figure 3. Synthesis of complexes of ligands L , L , L and L


Synthesis of L* and L^

To a solution of 4-aminoantipyrine (20 mmol, 4.06 g) dissolved in 100 mL of hot ethanol, acetylacetone (10 mmol, 1.03 mL) was added and the mixture refluxed for half an hour in a round bottom flask. On cooling this mixture to room temperature, a light-orange precipitate was obtained

L' or L (prepared in situ)

M'Cl,

n = 0 for L' n = 3 for L M' = Fe(III), Crail)

L or L (prepared in situ)

n = OforL^ n = 1 for L M' = FeaiI),Cr(ra)

H5C,

M'Cl,

H .COOH

^ ^CH2C00H ,N CI N c " ,CH3

^ ^CH, CI

1 T 2 T 3 Figure 4. Synthesis of complexes of ligands L , L , L and L


(Figure 1). It was redissolved in THF (100 mL) and 1,6-diaminohexane (10 mmol, 1.16 g) or 1,3-dianiinopropane (10 mmol, 0.85 mL) were then added and the mixture was refluxed for about 10 h. It was then cooled to 0 °C and an excess of 0.1 molar HCl (20 mL) was added to cause precipitation. The product was thoroughly washed with diethyl ether and dried in vacuo. Yield 1.27 g for L (25%) and 1.48 g for L^ (27%).

Synthesis of L^ and L"*

A mixture of 4-aminoantipyrine (20 mmol, 4.06 g) and 1,3-diaminopropane (10 nraiol, 0.85 mL) or ethylenediamine (10 mmol, 0.66 mL) in 100 mL ethanol was refluxed for about 20 h. It was cooled to 0 °C and acidified with 20 mL of 0.1 molar HCI which afforded a brown product. It was redissolved in hot ethanol (100 mL) and benzoylacetic acid (20 mmol, 3.2 g) was added to it .It was further refluxed for about 30 h and then cooled to 0 °C followed by the addition of 0.1 molar (20 mL) HCl which yielded a precipitate (Figure 2). It was washed thoroughly with ethanol and dried in vacuo. Yield 1.81 g for L (25%) and 1.7 g for L^ (23%).

General Methods for the Synthesis of Complexes

Initially we tried to synthesize the complexes by adding the metal salts to ligand solution, however the yields were poor (10 to 15%). To overcome this problem, the complexes were synthesized in situ, in which salts were inunediately added to the solution of ligand under preparation (Figures 3 and 4).

Acetylacetone (2 mmol, 0. 20 mL) was added drop-wise to an ethanolic solution (50 mL) of 4-aminoantipyrine (4 mmol, 0.80 g). After refluxing this mixture for about half an hoiu* 1,6-diaminohexane (2 nunol, 0.23 g) was added and further refluxed for 24 h. The mixture was then cooled to 0 °C and hydrated metal chloride (2 nunol) in ethanol (25 mL) was added which afforded brisk precipitation of coloured complexes. It was filtered, washed with cold ethanol and dried in vacuo.

ACKNOWLEDGMENT

One of the authors (F.R.) thanks the Council of Scientific and Industrial Research (CSIR) New Delhi for the award of JRF.


REFERENCES

1. Rawle, S.C; Clarke, A.J.; Moore, P.; Alcock, N.W. Ligands designed to impose tetrahedral co-ordination: a convenient route to aminoethyl and aminopropyl pendant arm derivatives of 1,5,9-triaza-cyclododecane. J. Chem. Soc. Dalton Trans. 1992, 2755.

2. Gunter, M.J.; Robinson, B.C. Purpurins bearing functionality at the 6,16-meso-positions: synthesis from 5,15-disubstituted meso-[P-(meth-oxycarbonyl)vinyl]porphyrins. Aust. J. Chem. 1990, 43, 1839.

3. Inoue, M.B.; Villegas, C.A.; Asano, K.; Nakamura, M.; Inoue, M.; Fernando, Q. New 12-membered and 24-membered macrocycles with pendant acetato groups and x-ray crystal structures of the copper(II) and manganese(II) complexes. Inorg. Chem. 1992, 31, 2480.

4. Alcock, N.W.; Balakrishnan, K.P.; Berry, A.; Moore, P.; Reader, C.J. Studies of pendant arm macrocycle ligands. Part 6 Synthesis of two penta-aza macrocyclic Ugands containing single pendant co-ordinating 2-pyridylmethyl and 1-pyrazolylmethyl arms, and characterisation of their nickel(II), copper(II), cobalt(II) and zinc(II) complexes. Crystal structure of {3,11 -dibenzyl-7-(2'-pyridylmethyl)-3,7,11,17-tetra-azabi-cyclo[l 1.3.1]-heptadeca-l-(17),13,15-triene}-zinc(II) perchlorate. J. Chem. Soc. Dalton Trans. 1988, 1089.

5. Bias, A.D.; Santis, G.D.; Fabbrizzi, L.; Licchelli, M.; Lanfredi, A.M.M.; Pallavicini, P.; Poggi, A.; Ugozzoli, F. Pyridines with an appended metallocyclam subunit. Versatile building blocks to supramolecular multielectron redox systems. Inorg. Chem. 1993, 32, 106.

6. Shimada, T.; Kodera, M.; Okawa, H.; Kida, S. Synthesis of 1,10,19,28-tetraoxa-4,7,13,16,22,25,31,34-octaazacyclohexatria-contane (L) and its complex [Cu4L(OH)4] [C104]4-2H20. J. Chem. Soc. Dalton Trans. 1992, 1121.

7. Cameron, J.M.; Harvey, H.B.; Soutar, I. Non-symmetrical teraaza macrocyclic complexes of nickel(II) and their binding to synthetic polymer supports. J. Chem. Soc. Dalton Trans. 1992, 597.

8. Parker, D. Tumour targetting with radiolabeled macrocycle—antibody conjugates. Chem. Soc. Rev. 1990, 19, 271.

9. Izatt, R.M.; Bradshaw, J.S.; Pawlak, K.; Bruening, R.L.; Tarbet, B.J. Thermodynamic and kinetic data for macrocycle interaction with neutral molecules. Chem. Rev. 1992, 92, 1261.

10. Geary, W.J. Molar conductances of coordination compounds. Coord. Chem. Rev. 1971, 7, 81.

11. Drew, M.G.B.; Binothman, A.H.; Mcfall, S.G.; Mcllroy, P.D.A.; Nelson, S.M. Seven-co-ordination in metal complexes of quinque-dentate macrocyclic ligands. Part 5. Synthesis and properties of


pentagonal-bipyramidal and pentagonal-pyramidal manganese(II) complexes and crystal and molecular structure of (2,15-dimethyl-3,7,10,14,20-penta-azabicyclo-[ 14.3.1 Jeicosa-1 (20),2,14,16,18-pen-taene}-bis(isothiocyanato)manganese(II). J. Chem. Soc. Dalton Trans. 1977, 438.

12. Veggal, F.C.J.M.V.; Harkema, S.; Bos, M.; Verboom, W.; Staveren, C.J.v.; Gerritsma, G.J.; Reinhoudt, D.N. Metallomacrocycles: synthesis, x-ray structure, electrochemistry, and ESR spectroscopy of mononuclear and heterodinuclear complexes. Inorg. Chem. 1989, 28, 1133.

13. Daszkiewicz, B.K. Nickel(II) complexes of novel tetraaza macrocycUc ligands bearing pendant donor groups. J. Chem. Soc. Dalton Trans. 1992, 1673.

14. Nanda, K.K.; Das, R.; Newlands, M.J.; Hynes, R.; Gabe, E.J.; Nag, K. Phenoxo-bridged dinickel(II) complexes of a macrocyclic ligand: synthesis, stereochemical equilibria and structure. J. Chem. Soc. Dalton Trans. 1992, 897.

15. Lewis, J.; Wilkins, R.G. Modem Coordination Chemistry; Interscience: New York, 1960; 406.

16. Ballhausen, C.J. Introduction to Ligand Field Theory; Mc Graw Hill. New York, 1962; 253.

17. Resenfeld, S.; Williams, A. Benzoylacetic acid: synthesis and examination of the tautomeric equilibrium. J. Chem. Educ. 1991, 68, 66.

18. Reilley, C.N.; Schmid, R.W.; Sadek, F.S. Chelon approach to analysis (1) survey of theory and application. J. Chem. Educ. 1959, 36, 555.

19. Vogel, A.I. Text Book of Quantitative Inorganic Analysis; Longmans Green, 1986; 507.

Received October 4, 2001 Referee I: K. Moedritzer Accepted July 12, 2003 Referee IL M. W. Smith

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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY Vol. 34, No. l,pp. 93-99, 2004

Preparation of the Two Isomers of Cu(dien)Cl2

K. S. Siddiqi,* Fouzia Rafat, and Sadat H. Kar

Department of Chemistry, Aligarh Muslim University, Aligarh, India

ABSTRACT

Two isomers of [Cu(dien)Cl2] of two different colours (blue and yellow), where dien = diethylenetriamine have been isolated. They have been synthesized by a slight variation in the procedure. Both complexes turn blue in aqueous, ethanolic and DMSO solutions and attain a stable geometry. The blue isomer is thermally more stable than the yellow one. Both of them have identical electronic spectra and e values in solution.

Key 'Words: Cu(dien)Cl2; Synthesis; Colour.

*Correspondence: K. S. Siddiqi, Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India; E-mail: [email protected].

93

DOI: 10.1081/SIM-120027319 0094-5714 (Print); 1532-2440 (Online) Copyright 'V) 2004 by Marcel Dekkcr, Inc. www.dekker.com



94 Siddiqi, Ralat, and Kar

INTRODUCTION

ll is known that dielhylenetriamine (dien) may act as a tiideniate ligand and may coordinate with either a bent or planar conformation of the Hgand molecule.'" In addition, for complexes of the type lCii(dien)2X2l, the reluctance of Cu(II) ion to occupy a regular octahedral ligand environment would permit even more molecular structures. The isolation of a scries of [Cu(dien)2X2j (X = CK NO3) complexes by Stephens'"' with at least two different types of solid state electronic spectra would permit even more possible molecular structures for [Cu(dien)]"'^. The possibility of the formation of a series of compounds of Cu(II) with dien in 1:1 molar ratio having different colours and different stereochemistry has not been explored. We have, therefore, attempted the synthesis of complexes of Cu(II) with dien in order to see of it yields more than one complex of the same composition but different physical properties.


By varying the methods of synthesis, dien yielded a set of two complexes of different colours, blue and yellow, but with the identical composition [Cu(dien)Cl2].

CuCb + dien - ^ ^ [Cu(dien)Cl2]

Both complexes turn blue in aqueous, ethanolic and DMSO solutions although in the solid state they are stable with sharp melting points. Both of these could not be recrystallized because they give only a blue solution which becomes sticky after keeping for fifteen days. The change in colour and other physical properties of the complex is due to non-planarity of the dien. Although the changes are very small, they have a considerable effect on the geometry of the complex. The electronic spectra of both complexes in solution are identical with a common peak around 600 nm. The e values range between 2.32-2.35Lmor 'cm"' .

It is noteworthy that a slight variation in the method of synthesis make a difference in the colours and melting points of the complexes. Analytical data and molar conductance of the complexes are given in Table 1. The complexes were dried at about 100 °C before analysing them.

The change in colour is due to a change in coordination geometry of the complex (Fig. 1). As a consequence of a change in the position of the nitrogen atom of the dien molecule, there is a change in the colour of the isomers. Also

Two Isomers of Cu(dien)Cl2 95

r i

u c V

•o 3 U ^4-1

o t/1 u (U

s o on • i » -

U

:S t ( - i O

o o 4->

3

^ - v

"d o ca o

T) C 3 O •a ^ c/T •f—( CA

>-.

< T3

O

o

i T5 G a

13 o •a

c

V

c ca 3

T3

o o

s

j

"o E E O

1 1

E O

X O (D

S

o to

2 Q

u

X

u

1

u o

E o 1/3

in

lO

(N

00

in

00

>n

o d

VO

CO

in

c in

in

00

ON

m <N

c

00

ON

>n

in

(N o d

in ON

m

2 3

u u --m in

= u d

00

en

z 3

u u -

CQ

96 Siddiqi, Rafat, and Kar

\ /

Figure 1. Possible geomcirica! variation in [Cii(dien)Cl2l.

from the co'stal and molecular structure of blue [Cu(dien)(N03)2l, it has been confirmed that the geometry of Cu(II) is square-pyramidal.'"'"

The molar conductance of one millimolar solution of the complexes in DMSO and MeOH at room temperature is intermediate between a 1:1 and 1:2 electrolyte'"^' (Table 1). This is possibly due to stepwise dissociation of the complex in solution where the equilibrium is largely shifted towards the right. Although the solvent molecule may occupy the place of chlorine to maintain the square-planar geometry of the complex in solution.

[Cu(dien)Cl2l -^ fCu(dien)Cl]+ + Ci"

(Cu(dien)C]J+ - ^ [Cu(dien)]-+-j-CP

Electronic Spectra

The electronic spectra of both complexes in DMSO are similar (Table 2). They show a common peak at 255 nm which moves slightly towards 262-267 nm on dilution (log e = 3.39). The lower-energy bands (612-627 nm) are broad and weak and are assigned to d -d transition. The high energy band is most probably due to the dien molecule. Since the two isomers turn blue in

Table 2. Colour of the solid, solution, absorption bands and log e of the isomers.

Colour of the solid

Solution colour

Wave length (nm)

Logs (DMSO)

.mo ' cm- ' ) Wave length

(nm)

Loge (MeOH)

L mol ~' cm - '

Yellow Blue

Blue Blue

255 256

3.39 3.39

612 629

2.32 2.35

Two Isomers of Cu(dicn)CU 97

DMSO and McOH, it is believed that, in solution, both complexes achieve square-planar geometry.

It is concluded that the change in physical properties of [Cu(dien)Cl2] is due to (he non-planarily of the dien molecule.

IR Spectra

The IR spectrum of the free dien molecule exhibits two bands (3360-3295cm"') which are shifted to lower wave number after chelation (3280-315()cm "') and 3230-3020cm"'). They are assigned to the primary and secondary amino groups, respectively. It is evident that the dien molecule is coordinated in a tridentate manner. A very strong band at 660-980cm~' has been obser\ ed for both complexes. There are two more prominent bands at 1030-1035 and 1085-1180cm"'. The IR spectrum of the yellow complex recorded in air shows a band at 1180 cm'' ' which does not change even after six weeks while the blue complex shows a band at 1085 cm"' which also does not change within this time period. These minor differences support the existence of isomers of [Cu(dien)Cl2] probably due to a slight change in Cu dien bond lengths (Fig. 1).

EPR Spectra

From the IR spectral study, it has been shown that Cu(II) appears to be five-coordinate but from the EPR study interaction between two copper atoms of different units has been observed. This is possible only if bridging between two such moieties occurs as shown below (Fig. 2).

Also, the bridging between two Cu(II) atoms does not alter the geometry of the complex as suggested by EPR. For the yellow complex, one broad signal is observed, possibly due to Cu(II)-Cu(II) dipolar interactions. The flow of electrons from chlorine to metal and back (Fig. 2) may produce a dipole on

HN Cu'

Ho

H, CI N \

^Cl

Cu NH

ci Ho

Figure 2. The bridged structure of [Cu(dien)Cl2].

98 Siddiqi, Rafat, and Kar

one metal which niuy interact with the other Cu(II) ion of the opposite dipole. The value of g for the yellow complex is 2.109 Gauss.

For the blue complex, only one site of Cu(II) with gj and g|| components is observed. The dipolar interaction between Cu(II)-Cu(II) does not obliterate the g^ amd g components. The value of the gj component for this complex is 2.184 Gauss and the value of gy is 2.051 Gauss.

EXPERIMENTAL

To a solution of CuCl2-2H20 (lOmmol, 1.7g) in methanol (15 mL), diethylenetriamine (lOmmoI, 1.0g) in methanol (15mL) was added. The resulting blue mixture was left for three hours at room temperature when it yielded a blue crystalline compound. It was filtered, washed with cold methanol and dried over CaC^ in vacuo. Yield, 1.2 g (44%).

For the synthesis of the yellow complex "a L4 aqueous methanolic solution (25 mL) of diethylenetriamine (lOmmoI, l.Og) was added to the methanolic (15 mL) solution of CuCl2-2H20 (lOmmol, 1.7 g). The pH of the mixture was adjusted to 2 by the addition of 0.1 M HCI which was monitored by a pH meter. The resulting green mixture was evaporated to dryness which yielded a yellow amorphous compound. It was filtered, washed with an ice-cold 1:2 ethanol-methanol mixture and dried over CaCl2 in vacuo. Yield, 0.9 g (33%).

ACKNOWLEDGMENTS

One of the authors (F.R.) thanks the Council of Scientific and Industrial Research (CSIR) New Delhi for the award of Junior Research Fellowship and to Prof. R.J. Singh, Department of Physics, A.M.U., Aligarh, India for a fruitful discussion of the EPR spectra.

REFERENCES

Cotton, F.A.; Wing, .R.M. Crystal and molecular structure of cis-(diethylenetnamine)molybdenum tricarbonyl-dependence of Mo-C bond length on bond order. Inorg. Chem. 1965, 4, 1328. Stephens, F.S. Structures of diethylenetriamine copper(II) cations. Part I. Crystal structure of bis(diethylenetriamine) copper(II) nitrate. J. Chem. Soc. A 1969, 883.

Two Isomers of Cu(dien)Cl2 99

3. Allmann. R.; Krestl, M.; Bolos, C ; Manoussakis, G.; St. Nikolov, G. The crystal and molecular structure of (diethylenetriamino)copper(II) nitrate. Inorg. Chim. Acta. 1990, 175, 225.

4. Bew, M.J.; Fereday, R.J.; Davey, G.; Hathaway, B.J.; Stephens, F.S. The x-ray crystal structure and electronic energy levels of the square-pyramidal /x-formatomonodiethylenetriamine copper(II) formate. Chem. Commun. 1970. 887.

5. Geary, W.J. The use of conductivity measurements in organic solvents for the characterisation of coordination compounds. Coord. Chem. Rev. 1971, 7,81.

Received July 8, 2000 Referee I: J. D. Zubkowski Accepted August 30, 2003 Referee II: E. J. Valente

SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY Vol. 34. No. 4. pp. 16^-114, 2004

Synthesis and Characterization of Trinuclear Complexes Containing

Cu(II) and Ti(IV)

Fouzia Rafat, K. S. Siddiqi,* and Lutfullah

Department of Chemistry. Aligarh Muslim University, Alisarh. U.P., India

ABSTRACT

Heterotrinuclear complexes of the type [Cu(ppn)2Cl2{Ti(Cp)2}2] and [Cu(en)2(N03)2{Ti(Cp)2}2] have been synthesized and characterized by elemental analyses, IR, electronic. EPR, and ' H N M R spectra, magnetic moments, and conductivity measurements. The results indicate that the trinuclear complexes are covalent with an octahedral environment around the copper(II) ion, while its mononuclear analogues, [Cu(ppn-H2)2]Cl2 and [Cu(en-H2)2](N03)2, are square-planar and ionic in nature.

Key Words: Trinuclear; Heterometallic; Electrochemical; Spectroscopic studies.

*Correspondence: K. S. Siddiqi, Department of Chemistry, Aligarh Muslim University, Aligarh 202 002, U.P., India; E-mail: [email protected].

763

DOl: 10.1081/SIM-120035955 0094-5714 (Print); 1532-2440 (Oxiline) Copyright 'i') 2004 by Marcel Dekker. Inc. www.dekker.com



764 Rafat, Siddiqi, and Lutfullah

INTRODUCTION

The design of heteronuclear compartmental ligands capable of binding two or more metal ions in close proximity are important for providing functional heterometallic molecules. The growing interest in electrochemical, magnetic, and spectroscopic studies of multimetallic complexes is due to their importance in inorganic and bioinorganic chemistryJ'"^' They are universally available in nature as active sites in a variety of metalloenzymes'"*^ and play a significant role in catalysis. Many of the complexes are also used as cocatalyst in metal-catalyzed polymerization processes.^^' Copper complexes with a variety of ligands have been used in the binding and activation of CO, NO, and OT and as models for metalloenzymes.^^'^' Recently, some dinuclear complexes have been shown to exhibit catalytic activity for water oxidation to evolve oxygen.^ ' Furthermore, they provide interesting cases for the study of magnetic interactions'^''°' and may also serve as models for some mclalloproteins. Multimetallic complexes containing cyclopentadienyl rings have attracted increasing interest in the chemistry of metal complexes.'"^ Currently! several efforts have been made to facilitate the synthesis of planar, chiral cyclopentadienyl metal complexes in terms of their potential as mediators or catalysts in asymmetric organic synthesis. '' ^ Planar, chiral cyclopentadienyl metal complexes have advantages as catalyst since coordination of a cyclopentadienyl ligand to a metal atom is generally so strong that there is almost no chance of ligand dissociation resulting in race-mization. In fact, planar, chiral cyclopentadienyl Group IV metal complexes were successfully used as catalysts in asymmetric organic synthesis and polymerization.''"^'

In the current communication, the synthesis and characterization of heterotrinuclear complexes of the type [Cu(ppn)2Cl2{Ti(Cp)2}2] (2) and [Cu(en)2(N03)2{Ti(Cp)2}2] (4) are reported, where ppn-H2 = 1,3-diaminopro-pane, en-H2 = 1,2-diaminoethane, and Cp = cyclopentadienyl.


Heterobimetallic complexes are of current interest due to their unique physicochemical properties and functions arising from interaction or interplay of dissimilar metal ions in close proximity""'^ with each other.

New Cu(II) and Ti(IV) heterotrinuclear complexes, based on multi-dentate polyamine ligand and linked by Ti atoms on both sides were synthesized in order to better correlate structure and magnetic properties. The use of mononuclear species as building blocks has been made, such

Trinuclear Complexes 765

as [Cu(ppn-H2)2]Cl2 (1) and [Cu(en-H2)2](N03)2 (3) in which ppn-H2 and en-H2 act as bidentate ligands blocking all the coordination sites. The amino hydrogen of polyamines can be easily replaced by the addition of (Cp)2 TiCl2 resulting in the formation of heterotrinuclear complexes. All the heterotrinuclear complexes have been isolated in good yield and fully characterized. The reaction of the complexes [Cu(ppn-H2)2]Cl2 (1) and [Cu(en-H2)2](N03)2 (3) with (Cp)2TiCl2 gives the heterotrinuclear chelates [Cu(ppn)2Cl2{Ti(Cp)2}2] (2) and [Cu(en)2(N03)2{Ti(Cp)2}2] (4), respectively. The complexes are formed by the replacement of amino hydrogen by Ti(IV) according to the scheme in Fig. 1.

Molar conductance measurements of (1) and (3) in MeOH suggest them to be 1:2 electrolytes while the heterotrinuclear chelates [Cu(en)2(N03)2 {Ti(Cp)2}2] (4) and [Cu(ppn)2Cl2{Ti(Cp)2}2] (2) are non-electrolytes in DMSO (Table 1). " ^

C1JCI2.2H2O H2N NH2

n H2N NH2

X HjN NH2 u

-4HC1

Cb

2(CphTCk

c/ V V \p

Figure 1. Synthesis of trinuclear complex (2).

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2. i3 i i -S o O- >

00

C f~' O

u u '

-c U =C

"3' <) "s

m 0 CN

0 CN CN

c 4) 1)

o

(M O

' S ON

0C5 U VO

r~; . ^ ^^ o H .i:'

P, O o ^

t r s <s

O 2 3

U

cs f«^


IR Spectra

The IR spectra (Table 2) of primary amines show two N-H stretching frequencies in the range 3300-3500cm~', which are shifted to lower frequency on chelation. In compounds (1) and (3) these bands appear in the range 3200-3300 cm~' indicating chelation of Cu(II) with ppn-Ho and en-Ho. However, in compounds (2) and (4) a single absorption band appears at 3013 and 3232cm~', which is attributed to i'(N-H) of the coordinated secondary amine,' '•''' one of the hydrogen from en-Ho or ppn-Hi was replaced by Ti(IV).

Since only one absorption band at 1387 cm~' has been observed for [Cu(en)2](N03)2, it is suggested that the NOJ group is not bonded to metal in this case. In the case of [Cu(en)2(N03)2{Ti(Cp)2}2] (4), four bands assigned to the NO^ absorption frequency have been observed at 1510, 1384, 1041, and 815 cm~' (Table 2), which indicate the coordination of NO^ to metal ion."^' It is also supported by v(Cu-O) at 487 cm~' which is absent in compound (3).

It is difficult to distinguish between uni- and bidentate nitrate ligands because they both have the same symmetry. However, from a study of metal nitrates''^' it has been shown that the difference between symmetric and asymmetric [A(as-s) NO3] stretch is small (150-250cm~') when NOJ is unidentate while for a bidentate NOJ group bonded to a metal ion, the difference of asymmetric minus symmetric frequencies [A(as-s)] is very large '*^ (300-400cm"'). Recently, Fujisawa ' ^ et al. have studied the type of nitrate binding mode depending upon the separation between the VasCNOs) and Vs(N03) frequencies. They further corroborated their results by x-ray crystal structures of nitrato copper(II) complexes of rm(pyrazolyl)-borate. In our case, in the complex (4) A(as-s) is of the order of 126 cm"' compared to 300-400cm"' for a bidentate NOJ group, which is suggestive of a unidentate NOJ group which renders Cu(II) octahedral although distortion may occur.

Table 2. Absorption bands (cm ') of complexes of copper.

v(N03) v(N03) Compounds v(N-H) v(C-N) asym. sym. v(NO)

(1) [Cu(ppn-H2)2]Cl2 3,352 m 1,213 w — — — 3,222 m

(2) [Cu(ppn)2Cl2][Ti(Cp)2]2 3,013 m 1,183 w _ _ _ (3) [Cu(en-H2)2](N03)2 3,372 m 1,041 w — 1,387 s —

3,217 m (4) [Cu(en)2(N03)2][Ti(Cp)2]2 3,232m 1,125 w 1,510m 1,384s 1,041m

Electronic Absorption Spectra

The electronic spectra of complexes (1) and (3) were recorded in MeOH and those of (2) and (4) in DMSO (Table 3). On the basis of molecular orbital calculations three to four absorption bands have been predicted in the case of Cu(ll) complexes with square-planar geometry.'""' However, in most cases, Cu(ll) complexes exhibit only one d-d band in the 15,000-18,000 cm"' region.'"'"' De Rose and Courenkers'""'' have shown in a study of a Cu(II) complex with peptide the appearance of only one d-d band at 550 nm besides chai'ge transfer. We, too, have observed only one d-d band in the case of complex (1) and (3) in the above range, which is consistent with a square-planar geometry of Cu(II).

The i»w-cyclopentadienyltitanium derivative of [Cu(ppn-H)2]Cl2, i.e., (2) shows a charge transfer band at 306 nm and a broad d-d-absorption band at 898 nm, which is entirely different from that of the complex (1). Such absorption bands are generally observed for octahedral Cu(II) complexes.'"" ' The UV-VIS spectrum of (4) displays an absorption band at 325 nm, which is assigned to the NOJ -^ Cu(II) charge transfer. ' ^ In the ligand field region, the d-d band has been observed at 647 nm, which is consistent with an octahedral geometry for the Cu(II) complex. Stephens^^^^ has also reported a distorted octahedral geometry for the Cu(II) complex with diethylenetriamine.

Magnetic moment values of (4) and (2) are very close to those calculated for one unpaired electron (Table 3). Electronic absorption spectra and magnetic moments are suggestive of an octahedral geometry around Cu(II) although distortion of the octahedron may occur due to the Jahn-Teller effect. Thus, on moving from mononuclear to the trinuclear complexes (2), (4) there is a shift in d-d transition which is ascribed to the change in coordination number and environment around the Cu(II) centre.

Table 3. Magnetic susceptibility, electronic spectral bands, and e values in DMSO of complexes (2) and (4) while in MeOH for complexes (1) and (3).

Compounds

(1) [Cu(ppn-H2)2]Cl2

(2) [Cu(ppn)2Cl2][Ti(Cp)2]2

(3) [Cu(en-H2)2](N03)2

(4) [Cu(en)2(N03)2][Ti(Cp)2]2

Meff (B.M.)

1.93

1.73

1.87

1.79

Transition (nm)

250 590 306 898 246 571 373 647

Assignment

C.T.

C.T.

^2g <- Eg C.T.

C.T.

T2g •<- Eg

e (moP'cm^)

100 18

112 6

160 24

110 12

EPR Spectra

The EPR spectra of the poIyci7stalIine copper(II) complexes at room temperature showed a strong signal and their .'n. i 'j, and axial symmetry parameter {G = g\\ — l/gx. ~ -) have been calculated. No complex shows hyperfine structure at room temperature. This may be attributed to strong dipolar and exchange interaction between copper(II) ions in the unit cell. The room temperature g values of (4) {g^\ = 2.23 and gj_ = 2.065) and (3) ( n = 2.13 and gx = 2.07) suggest that d : - y:i may be the ground state for both of the complexes. Complex (1), {gn ~ 111 and gx_ = 1.90) also indicates that dx3-y2 may be the ground state, but for the complex (2) gy = 2.056 and ^ j , = 2.18 suggest that dz: may be the ground state. The Cu(II) ion may get strongly coordinated to C F , which may be responsible for the change of the character of the ground state resulting in a d : state.'^^'

The G value measures the exchange interaction between copper centers in the polycrystalline solid. If G > 4, exchange interaction is negligible and if G < 4, considerable exchange interaction occurs in the solid complexes. ^ For complexes (3) and (4) the G values are 1.857 and 3.55, respectively, which indicate a considerable exchange interaction in the complexes.

H NMR spectrum

' H NMR spectrum of complex (4) was recorded in DMS0-c?6 and showed signals at 8 8.29 (m) ppm, which is assigned to N-H protons, inferring replacement of one of the two NH2 protons and simultaneous coordination of nitrogen atom to Ti(IV). The signal at 8 7.2 (s) is due to cyclopentadienyl group. A multiplet at 5 2.8 (m) indicates the presence of methylene protons, which are coupled both by NH and adjacent methylene protons.

EXPERIMENTAL

1,3-Diaminopropane, 1,2-diaminoethane (Fluka), CuCl2- 2H2O (Merck), Cu(N03)2 • 3H2O (Loba), and Z7w(cyclopentadienyl)titanium dichloride (Aldrich) were used as received. THF was distilled and dried by conventional methods.

Elemental analyses (C, H, N) were carried out with a 1106 Carlo Erba analyzer. Chlorine was determined gravimetrically.'^^^ IR spectra (4000-450cm"') were recorded on a RXI FT-IR spectrometer as KBr discs. The conductivity measurements were carried out with a CM-82T Elico conductivity bridge in DMSO and MeOH. The electronic spectra were recorded on

770 Rafat, Siddiqi, and LutfuUah

a Cintia 5GBC speclropliolometer in DMSO and MeOH. Magnetic susceptibility measurements were one with a 155 Allied Research vibrating sample magnetometer at room temperature. The ' H N M R spectrum was recorded on a Bruker ACF 300 spectrometer at 300.12 MHz, using TMS as a reference in DMSO-Jft. EPR spectra of polycrystalline samples were recorded on a RE-2X Jeol EPR spectrometer fitted with 100 KHz field modulation.

Synthesis of [Cu(ppn-H2)2]Ci2 Complex (1)

CuCl2 • 2H2O (10 mmol, 1.7 g) dissolved in methanol (25 mL) was added to a methanolic solution (15 mL) of propanediamine (20 mmol, 1.64 g) at room temperature, which immediately yielded a -deep blue crystalline compound. Since the yield was increased by cooling, the contents were cooled to about 5 °C for 1 hr. It was then filtered, the residue washed with cold methanol and diethyl ether and dried over CaCU under vacuo. Yield, 3.4 g (85%).

Synthesis of [Cu(ppn)2Cl2{Ti(Cp)2}2] (2)

A suspension of [Cu(ppn-H2)2]Cl2 (0.005 mol, 1.4 g) in THF (20 mL) was treated with 20 mL of a THF solution of (Cp)2TiCl2 (0.01 mol, 2.48 g). A small amount of NH4CI was also added to facilitate the reaction. The mixture was refluxed on a water bath for about 24 hr, when a pale yellow product was obtained. The mixture was cooled to room temperature, filtered, the residue washed several times with ethanol and dried in vacuo. Yield, 1.7 g (55%).

Synthesis of [Cu(en-H2)2](N03)2 (3)

Cu(N03)2 • 3H2O (10 mmol, 2.41 g) dissolved in methanol (25 mL) was added to a methapolic solution (15 mL) of ethylenediamine (20 mmol, 1.22 g) at room temperature, which immediately yielded a violet crystalline compound. It was left at 5 °C for 1 hr, which increased the yield. It was then filtered, the residue washed with cold methanol and ether and dried over CaCl2 under vacuo. Yield, 2.5 g (90%).

Synthesis of [Cu(en)2(N03)2{Ti(Cp)2}2] (4)

A suspension of [Cu(en-H2)2](N03)2 (0.005 mol, 1.5 g) in THF (20 mL) at 50-60 °C was refluxed with (Cp)2TiCl2 (0.01 mol, 2.48 g) in the presence of

Trinutiear Complexes 771

a small amount of NH4CI, which yielded the green complex under reflux. The resulting mixture containing complex (4) was cooled to room temperature, filtered, and the residue washed several times with ethanol and dried in vacuo. Yield. 2.{)g(62%)(Fig. 2).

CONCLUSION

The results presented in this paper show that the reaction of a mononuclear Cu(ll) complex with CpiTiCli can be used in the preparation of a tri-nuclear complex. Evidence for trinuclear species was found in ' H N M R resonances in the spectrum of (2), which shows a prominent peak at 8 8.29 (m) ppm which is assigned to N - H protons, inferring replacement of one of the two NH2 protons of the polyamines and simultaneous coordination of nitrogen atom to Ti(IV). The spectrum also shows the peak due to the cyclo-pentadienyl group at 8 7.2 (s). Evidence for trinuclear complexes may also be

Cu(N03)2'3H20 + HjN NHa

H2N mh

H2N NH2

-4HC1

(N03)2

2(Cp)2rici2

H NO3

\r Cp, N

c/V

H 1/ A /'

Cu Ti N Cp

NO3

Figure 2. Synthesis of trinuclear complex (4).


seen by the IR spectra of (2) and (4) which show a single band at 3013 and 3232cm~', respectively, which are attributed to v(N-H) of the coordinated secondary amine, as one of the hydrogens en-H2 or ppn-H2 was replaced by Ti(IV) resulting in the formation of trinuclear complex. These findings lead us to believe that (2) and (4) are trinuclear complexes. The studies presented in this paper have focused on the synthetic scope of the use of Cp2TiCl2 as a base. Upon binding of Cp^TiCU to the mononuclear Cu(II) complexes, there is a change in the geometry of the Cu(II) ion. Electronic spectra reveal square-planar geometry around Cu(II) for the complexes for (1) and (3) while an octahedral geometry is observed for the trinuclear complexes (2) and (4). EPR spectra show a change in the character of the ground state as we move from (1) to (2) indicating the distortion due to the attachment of Cl~(l). Molar conductance measurements suggest an ionic bond for (1) and (3) while a covalent bond for (2) and (4) has been observed.

ACKNOWLEDGMENT

One of the authors (F. R.) thanks the Council of Scientific and Industrial Research (CSIR) New Delhi, for the award of Junior Research Fellowship and to Prof. R.J. Singh of the department of physics for running the EPR spectra.

REFERENCES

Telfer, S.G.; Bocquet, B.; Williams, A.F. Thermal spin crossover in binuclear iron(II) helicates: negative cooperatively and a mixed spin state in solution. Inorg. Chem. 2001, 40, 4818-4820. Kodera, M.; Taniike, Y.; Itoh, M.; Tanahashi, Y.; Shimakoshi, H.; Kano, K.; Hirota, S.; lijima, S.; Ohba, M.; Okawa, H. Synthesis, characterization and activation of thermally stable /x-l,2-peroxodiiron(III) complex. Inorg. Chem. 2001, 40, 4821-4822. Herbst, K.; Monari, M.; Brorson, M. Heterobimetallic, cubane-like MO3S4M' cluster cases containing the noble metals M' = Ru, Os, Rh, Ir. Unprecedented tri-(/x-carbonyl) bridge between ruthenium atoms in [{r7' -Cp')3Mo3S4Ru}2(At-Co)3] - . Inorg. Chem. 2001, 40, 2979-2985. Hart, P.J.; Balbirnie, M.M.; Ogihara, N.L.; Nersissian, A.M.; Weiss, M.S.; Valentine, J.S.; Eisenberg, D. A structure-based mechanisms for copper-zinc superoxide dismutase. Biochemistry 1999, 38, 2167-2178. Chen, E.Y.; Marks, T.J. Cocatalysts for metal-catalysed olefin polymerisation: activators, activation processes, and structure-activity relationships. Chem. Rev. 2000, 100, 1391-1434.

rriiuiclcar Complexes 773

6. Beneaii. L.M.; Halfen, J.A.; Young, V.G.; Tolman, W.B. Heterocyclic donor inlluences on the binding and activation of CO, NO and O2 by copper complexes of hybrid triazacyclononane-pyridyl ligands. Inorg. Chim. Acta 2000, 297, 115-128.

7. Halfen. J.A.; Jazdzweski, B.A.; Mahapatra, S.; Berreau, L.M.; Wilkinson, E.C.; Que, L.; Tolman, W.B. Synthetic models of the inactive copper(Il)-iyrosinate and active copper(II)-tyrosyl radical forms of galactose and glyoxal oxidases. J. Am. Chem. Soc. 1997, 7/9, 8217-8227.

8. Nagoshi, K.; Yagi, M.; Kaneko, M. Analysis of water oxidation catalysis by dinuclear ruthenium complex [(NH3)5Ru-0-Ru(NH3)5]'^'^ incorporated in a nafion membrane. Bull. Chem. Soc. Jpn 2000, 75, 2193-2197.

9. Tercero, J.; Diaz, C; Fallah, M.S.E.; Ribas, J.; Solans, X.; Maestro, M.A.; Mahia. J. Synthesis, characterization and magnetic properties of self-assembled compounds based on discrete homotrinuclear complexes of Cu(ll). Inorg. Chem. 2001, 40, 3077-3083.

10. Gao, E.: Tang, J.; Liao, D.; Jiang, Z.; Yan, S.; Wang, G. Oxamato-bridged trinuclear Ni"Cu"Ni" complexes with irregular spin state structures and a binuclear Ni"Cu" complex with an unusual supramolecular structure: crystal structure and magnetic properties. Inorg. Chem. 2001, 40, 3134-3140.

11. Hair, G.S.; Jones, R.A.; Cowely, A.H.; Lynch, V. Group and zwitterionic metallocenes based upon the bridged amido-cyclopentadienyl ligand and coordinated dienes. Inorg. Chem. 2001, 40, 1014-1019.

12. Grotjah, D.B.; Lo, H.C.; Dinoso, J.; Adkins, CD.; Li, C ; Nolan, S.P.; Hubbard, J.L. Studies of the synthesis and thermochemistry of coordina-tively unsaturated chelate complexes (Tj -C5Me5)IrL2 (L2 = TSNCH2 CH2NTS, TSNCH2CO2, CO2-CO2). Inorg. Chem. 2000, 59, 2493-2499.

13. Nakamura, Y.; Yonemura, M.; Arimura, K.; Usuki, N.; Ohba, M.; Okawa, H. Tetranuclear mixed-metal M^Cu" complexes derived from a phenol-based macrocyclic ligand having two N(amine)202 and two N(imine)202 metal-binding sites. Inorg. Chem. 2001, 40, 3739-3743.

14. Geary, W.J. Molar conductances of coordination compounds. Coord. Chem. Rev. 1971, 7, 81-107.

15. Suh, M.P.; Kang, S.G. Synthesis and properties of Ni(II) and Cu(II) complexes of 14-membered hexaaza macrocycles. 1,8-Dimethyl and 1,8-diethyl-l,3,6,8,13-hexaazacyclotetradecane. Inorg. Chem. 1988, 7, 2544-2546.

16. Rosenthal, M.R. The myth of the non-coordinating anion. J. Chem. Educ. 1973,50,331-335.

17. Field, B.O.; Hardy, C.J. Volatile and anhydrous nitrato-complexes of metals: preparation by the use of dinitrogen pentoxide and measurement of infrared spectra. J. Chem. Soc. 1964, 4428-4434.

774 Rafat, Siddiqi, and LutfuUah

18. Nakamato, K. IR and Raman Spectra of Inorganic and Coordination Compounds, 4th Ed.; John Wiley: New York, 1986.

19. Fujisawa, K.; Kobayashi, T.; Fujita, K.; Kitajima, N.; Moro-Oka, Y.; Miyashita, Y.; Yamada, Y.; Okamoto, K. Mononuclear copper(II) hydroxo complex: structural effect of a 3-position of /m(pyrazolyl) borates. Bull. Chem. Soc. Jpn 2000, 75, 1797-1804.

20. Cotton, F.A.; Harris, C.B.; Wise, J.J. Extended Huckel calculations of the molecular orbitals in Z?t5(ketoenolate) complexes of copper(II) and nickel(II). Inorg. Chem. 1967, 6, 909-915.

21. Downing, R.S.; Urbach, F.L. The circular dichroism of square-planar, tetradenlate SchilT base chelates of copper(II). J. Am. Chem. Soc. 1969, 5977-5983.

22. Kumagai, K.; Hasegawa, M.; Enomoto, S.; Hoshi, T. Electronic structure of N,A^'-/?/5(2-aminobenzylidene)ethylenediaminatocopper(II). Bull. Chem. Soc. Jpn 2001, 74, 441-447.

23. Daugherty,.R.G.; Wasowicz, T.; Gibney, B.R.; De Rose, V.J. Design and spectroscopic characterization of peptide models for the plastocyanin copper-binding loop. Inorg. Chem. 2002, 41, 2623-2632.

24. Figgis, B.N. Introduction to Ligand Fields; Wiley Eastern Limited; 1976; 218.

25. Stephens, F.S. Structures of diethylenetriamine copper(II) cations. Part 1. Crystal structure of ^/5(diethylenetrianiine)copper(II) nitrate. J. Chem. Soc. (A) 1969, 883.

26. Cotton, F.A.; Wilkinson, G.; Murillo, C.A.; Bochmann, M. Advanced Inorganic Chemistry, 6th Ed.; Wiley Interscience; 1999; 865.

27. Procter, M.; Hathaway, B.J.; Nicholls, P. The electronic properties and stereochemistry of the copper(II) ion. Part I. B/5(ethylenediamine) copper(II) complexes. J. Chem. Soc. (A) 1968, 1678-1684.

28. Vogel, A.I. Gravimetric analysis. In A Text Book of Quantitative Inorganic Analysis, 3rd Ed.; Longman: London, 1968; 460-468.

Received January 19, 2003 Referee I: M. E. Hagerman Accepted January 26, 2004 Referee II: W. T. Tikkanen

Polish J. Chem., 78, xxx-xxx (2004)

An Anionic Moiety, MCI4" (M = copper, zinc, cadmium and mercury) Stabilized by

Bis(diethylenetriamine)copper(II) Cation

by K.S. Siddiqi*', Fouzia Rafat', M.Y. Siddiqi^ LutfuUah' and Yonas Chebude'

^Department of Chemistry. Aligarh Muslim University, Aligarh 202002, India E-mail: [email protected]

^Research Center, College of Sciences, KingSaud University, Riyadh 11451, KSA 'Department of Chemistry, Addis Ababa University, Addis Ababa-1176, Ethiopia

(Received April 26th, 2004; revised manuscript July 19th, 2004)

Bimetallic complexes of the type [Cu(dien)2][MCU], where M - Cu(II), Zn(n). Cd(II) and Hg(II), were prepared by reacting bis(diethylenetriamine)copper(U) dichloride with copper, zinc, cadmium and mercury dichlorides in cthanol. They have been characterized by elemental analyses, IR, electronic and EPR spectra, magnetic moment, TGA and conductivity measurements. Electrical conductivity of all the complexes indicated them to be 1:1 electrolyte in DMF and that the copper(II) ion is paramagnetic, mainUining its octahedral geometry, >\ ile metal ions in the anionic moiety of the complexes achieve their usual tetrahedral envu-onment. An augmented magnetic moment has been observed in the [Cu(dien)2][CuCU] complex, which is attributed to the ferromagnetic effect. From the EPR spectra, the Cu-Cu distance (rjO has been found to be larger in [Cu(dien)2][CdCU] than in [Cu(dien)2][CuCU]. The TGA of [Cu(dien)2][CuCl4] showed the decomposition of various figments between 226 to 1000*C.

Key words: bimetallic complexes, ferromagnetic effects, spectroscopic measurements

The diethylenetriamine (dien) is known to form two fused five-membered rings with metal ions [1-2]. The [Cu(dien)2](N03)2 is known to have a tetragonally distorted octahedral [Cu(dien)2] ''' imit with C2 symmetry and uncoordinated NOJ groups [3]. However, tetracoordinated complexes in which all ligands bonded to the core are halogen atoms, are also established. Bailer and Busch term such compounds as strictly halide complexes [4]. The synthesis and stabilization of such complexes is a recent matter of concern [5-6]. Schrobilgen and coworkers have reported the synthesis and stabilization of tetrachloroarsonium cation and tetrabromoarsoniimi cation using the weakly coordinating bulky anion as counterion [5]. A family of cyano bridged copper(II)-copper(I) mixed valence polymer containing diamine ligands of formula [Cu(pn)2] [Cu2(CN)4] has been prepared with the aim of analyzing how their architecture may be affected by steric constraints imposed by the diamine ligand [7].

Author for corresijondence.


K.S. Siddi^i et al.

We report here the synthesis, characterization and stabilization of bimetallic compounds of the type [Cu(dien)2][MCl4], where M = Cu(II), Zn(II), Cd(II) and Hg(n).

\ .

«Cl2

"CD

2©

w »

there U = Cu(n). Zn(II). Cddl) and Hg(II)

Scheme l.Synthesis of bimetallic complexes.

EXPERIMENTAL

Diethylenetriamine and hydiated metal chlorides (BDH) were used as received. Elemental analyses were carried out with a Perldn Elmer, SeriesII CHNS/0 analyzer 2400, USA. Chloride was determined gravimetrically as AgCl [8]. IR spectra (4000-200 cm~') were recorded on aKXIFT-IR spectrometer as KBr discs. The conductivity measurements were carried out with CM-82T Elico conductivity bridge in DMF. The electronic spectra were recorded on a Cintra SOBC spectrophotometer in DMF. Magnetic susceptibility measurements were done with a 1SS Allied Research vibrating sample magnetometer at room temperature. EPR spectra of copper complexes were recorded on a RE-2X Jeol EPR, spectrometer fitted with 100 KHz field modulation. The TGA was performed with a Perldn Elmer thermal analyzer. The experiment was done in nitrogen atmosphere using calcinated AI2O3 as reference material. The weight of the sample taken was 8 mg and the heating rate was 10*C min~'.

Synthesis of [Cu(dien)2]Cl2. CuCl2-2H20 (10 mmol, 1.7 g) dissolved in methanol (25 mL) was added to a methanolic solution (IS mL) of diethylenetriamine (20 mmol, 2.17 mL) at room temperature, which immediately yielded a blue crystalline compound. Since the yield was increased by couling, the contents were cooled to about 5°C for Ih. It was then filtered, washed with cold methanol and diethyl ether and dried over CaCl2 under vacuo. Yield (71%), m.p. 190*C.

An anionic moiety, MClj~ (M = copper, zinc, cadmium and mercury)... 3

Synthesis of [Cn(dien)2][MCl4]. Amethanolicsolutionof divalent metal chlorides of copper, zinc, cadmium or mercury was added to (10 mmol) [Cu(dien)2]Cl2 dissolved in MeOH (20 mL).The mixture was stirred for five minutes which resulted in the precipitation of coloured complexes.. The precipitate was removed by filtration, washed with McOH, diethylcthcr and dried over CaClj under vacuo. Yield (63-89%), m.p. 160-220'C.

RESULTS AND DISC^USSION Me

The reaction of cupric chloride (1 mol) with diethylenetriamine (2 mol) in E(pH yields bis(diethylenetriamine)copper(II) dichloride (equation 1). Further reaction of this compound with dichlorides of copper, zinc, cadmium or mercury yielded stable ionic bimetallic complexes (equation 2). It is apparent that these complexes are formed by the replacement of chloride ion from bis(diethylenetriaminc)copper(II) dichloride to the metal dichloride which results in the formation of a larger anion, MCl^", which is stabilized by the bis(diethylenetriamine)copper(n) cation.

Me B(bH

CuCb + 2dien • [Cu(dien)2]Cl2 (1) We KOH

[Cu(dien)2]Cl2 + MCI2 • [C:u(dien)2][MCl4] (2)

The elemental analyses correspond well to the proposed formulae of the complexes as [Cu(dien)2][MCl4], where M = Cu(II), Zn(II), Cd(II) and Hg(II). Conductivity measurements of 1 mmol solution of the bimetallic species in DMF (81-98 ohm"' cm^ mol"') fall exactly in the 1:1 electrolytic range [9]. The quantitative estimation of chloride ion as AgCl confirms the presence of fo;ir chloride in the bimetallic species.

Electronic absorption spectra. The magnetic moment values and electronic spectral bands and their assignments for the complexes are given in Table 1. All the Cu(II) complexes showed a broad d-d absorption band at 627 run assigned to the ^Tjg •- Eg transition which is characteristic of an octahedral copper(II) ion [10]. Stephens has also reported a distorted octahedral geometry for the Cu(n) complex with diethylenetriamine [3]. The position of d-d band remains unaltered while the absorption band in the UV region slightly varies for all of the bimetallic complexes. The absorption band at about 350 mn is unambiguously attributed to the charge transfer M° •- CI", revealing the presence of MClJ" species, in accord with the observations reported for CuCl4~ [11]. It is clear that the position of charge transfer band is blue shifted as the size of zinc group metal increases.

KS. Siddi^etaL

e I v-c

f

I

I

?

I O

en en

z

g^

<0 M t~ 00 M OO

a

s

S5

1 t I

An anionic moiety, A^l}~ (M " copper, zinc, cadmium and mercury)... 5

The magnetic moment values of the mononuclear and all the binuclear complexes, with exception of [Cu(dien)2][CuCl4] fallinthe 1.89 to 1.97 BM range, corresponding to one unpaired electron of copper(II) ion. This suggests that there is no remarkable influence of the d*° system of anc, cadmium and mercury on the single unpaired electron available on the copper(II) ion. Since the copper(II) ion is a d' system, the observed value should correspond to one unpaired electron. The observed magnetic moment for [Cu(dien)2][CuCl4] is 2.47 BM, which lies between the calculated value for one and two unpaired electrons but the tendency is more toward the latter. Since the complex contains two copper(II) ions, hence the expected observed//eff value should correspond to two impaired electrons, but 2.47 BM does not reach the value, which suggests that the complex ions are not arranged in regular tctrahedral symmetry leading to the zero orbital contribution to magnetic moment value. Since the anionic part has distorted tetrahedral geometry, thxis [Cu(dien)2] '*'unit also complies with the same degree of distortion in geometry.

IR spectra. It is difficult to distinguish NH frequency from NH2 frequency because they fall nearly in the same region. The IR spectrum of the free dien molecule exhibits two bands (3360-3295 cm"'), which are shifted to lower wave number after chelation (3135-3247 cm"' and 3235-3326 cm"'). Two sharp absorption bands at 1013 to 1085 and 1439 to 1455 cm"' arc due to v(C-C) and v(C-N) modes, respectively. A sharp peak at about 500 cm"' is assigned to v(Cu-N). All the bimetallic complexes show similar spectra, except that one additional IR band is observed in the 234-310 cm"' range, associated with the metal chlorine stretching &eq\ica.cy of the MCI4" moiety.

EPR spectra. EPR spectra of the precursor [Cu(dien)2]Cl2 and bimetallic complexes were studied and the following inferences were drawn. The spectra of [Cu(dien)2]Cl2, [Cu(dien)2][CuCl4] and [Cu(dien)2][CdCl4] complexes at room temperature showed a strong signal and their g| |, gx values have been calcxUated. The complexes did not show hyperfine structure at room temperature. It may be attributed to strong dipolar and exchange interaction between copper(II) ions in the unit cell. The room temperature g values of [Cu(dien)2]Cl2 (g| | = 2.052 and gx = 2.118), [Cu(dien)2][CuCl4] (g| | = 2.11 andgx = 2.035), and[Cu(dien)2][CdCl4] (g| | =2.215 and gx = 2.0523) indicated a tetragonal environment for the Cu(II) ion in each case. As g| I > gx for [Cu(dien)2][CdCl4] and [Cu(dien)2][CuCl4] the ground state wave function is indicated to be dx2_y2 but for the complex [Cu(dien)2]Cl2, gx > g 11 suggests that dz2 may be the groimd state. It means the ground state changes sharply during the formation of bimetallic complexes.

In the EPR spectra, the peak width can be explained by magnetic dipolar interaction with the neighboring Cu(II) ions. We may suppose, that there are fpur Cu(II) ions in the immediate neighborhood surrounding the central Cu(II) ion or each Cu(II) ion will interact magnetically with the four other nearest Cu(II) ions. According to the well known Van-Vleck formula [12] for polycrystalUne samples connecting line width with distance between the lines we have

K.S.Siddifetal.

( A V = 3/5g*^-^s(s + l)2kr- jk

where the symbols have their usual meanings, and in the simunation sign j represents the central ion and k runs from 1 to 4 corresponding to four nearest Cu(II) ions. But Van Vleck formula is correct jpid^lf there is only one signal in the EPR spectrum. In our case, two signals were obtained corresponding to gx and g| |. Using the method discussed in the book [13], the real width of the two signals was evaluated and then Van Vleck formula was applied. The distance (Cu-Cu) comes out to be rjk=6.24,5,87 and 6.92 A for [Cu(dien)2]Cl2, [Cu(dien)2][CuCl4] and [Cu(dien)2][CdCl4] complexes respectively. The Cu-Cu distance in all the three complexes is significantly higher. It means Cu does not form a M-M bond in all the three complexes. Further support comes from magnetic moment values. If the two Cu ions form a metal-metal bond these electrons will be paired and the complex will be diamagnetic. If they do not form a bond then the complex will be paramagnetic. All the three complexes are paramagnetic but the magnetic moment value for [Cu(dien)2][CuCU] complex measured at 25° is 1.23 BM per Cu atom, rather than the spin only value of 1.73 BM. This suggests that there is a weak interaction or weak coupling of the unpaired spins on the two Cu atoms in this complex [14].

TGA. Thermal analysis of [Cu(dien)2][CuCl4] was studied in the temperature range 0-1 OOO'C, using a combined thermogravimetric analyzer and differential thermal analyzer.

The thermogram of [Cu(dien)2][CuCl4] can be divided into two major portions showing weight loss of various components. The first step shows the weight loss of about 42.93% in the temperature range 226 to 484''C which compares well with the calculated value of 43.3 6% corresponding to two dien moieties. The second step runs steeply from 484 to 669''C showing a weight loss of nearly 42.65% which is equal to the anionic CuCU portion (43.22%). In the end, the residue left is copper metal (13.36%).

The DTA studies show that both the decomposition of organic moiety and anionic part are exothermic processes.

Acimowledgment

One of the autbots (]?. R.) thanks the Council of Scientific and Industrial Researdi (CSIR) New Delhi, for the award of Senior Research Fellowship and to Pro£ RJ. Singh, Department of Physics, Aligarii Muslim Univenity, Aligarh, India for a fiiuitful discussion of the EPR spectra.

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physicochemical studies of transition metal chelates · of macrocydic ligands and their transition...

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