1

CHAPTER I

INTRODUCTION

1.1 Introduction

Schiff base was first reported by Hugo Schiff in 1864 [1]. Compounds

containing an azomethine group (-CH=N-), known as Schiff bases are formed by

the condensation of primary amine with a carbonyl compound. Schiff bases of

aliphatic aldehydes are relatively unstable and are readily polimerizable while those

of aromatic aldehydes, having an effective conjucation system, are more stable.

Though the Schiff bases are stable solids, care should be taken in the purification

steps as it undergoes degradation. Chromatographic purification of Schiff bases on

silica gel is not recommended as they undergo hydrolysis. The common structural

feature of these compounds is the azomethine group with a general formula

RHC=N-R’, where R and R’ are alkyl, aryl, cycloalkyl or heterocyclic groups

which may be variously substituted. Presence of a lone pair of electrons in a sp2

hybridized orbital of nitrogen atom of the azomethine group is of considerable

chemical importance and impart excellent chelating ability especially when used in

combination with one or more donor atoms close to the azomethine group.

Examples of a few ligands are given in Figure 1.1.1.

Salen type, oxime type, macrocyclic type, Robson type, mixed type ligand.

2

Salen Type Ligand

Oxime Type Ligand

Macrocyclic Ligand

Robson type Ligand

3

Mixed type ligand complexes

Fig 1.1.1 Type of ligands and complexes.

1.1.1 Applications of Schiff base transition metal complexes

1.1.1.1 As electroluminescent materials

Organic electroluminescent (EL) devices are useful in novel-type flat-panel

displays since Tang and Van Styke first reported on high-performance organic EL

devices [2]. Their discovery was based on employing a multilayer device structure

containing an emitting layer and a carrier transport layer of suitable organic

materials. Organic dyes, chelate metal complexes and polymers are three major

categories of materials used in the fabrication of organic EL devices. Out of the

three, chelate metal complexes having high-luminance blue emitting nature find use

as materials for RGB (red, green, and blue) emission. Schiff base complexes,

especially those of Zn(II), are now a day’s used as electroluminescent materials

[3, 4]. Zinc complex of the Schiff base, N,N’-bis(2-hydroxy-1-naphthylidene)-3,6-

dioxa-1,8-diaminooctane, emits blue light with an emission peak at 455 nm having

maximum brightness of 650 cd m−2

, when it is used as the emitting layer in an

electroluminescence device. Fabrication of EL devices employing this kind of zinc

complexes as blue electroluminescent material was carried out by thermal vacuum-

4

deposition. Wei et al. prepared blue luminescent zinc and beryllium complexes of

the Schiff bases derived from calixarene [5]. These Schiff base complexes have

good solubility in normal solvents and can easily form thin films. Xie et al. reported

the crystal structure, thermal stability and optoelectronic properties of bis

[salicylidene (4-dimethylamino) aniline] zinc(II) [6]. This complex exhibits very

good light emission and charge transporting performance in organic light emitting

diodes (OLEDs). These experimental reports point to the possible application of

Schiff base complexes as emitting materials in full colour flat-panel displays.

1.1.1.2 In non-linear optical devices

Nonlinear optics (NLO) deals with the interactions of applied

electromagnetic fields with various materials to generate new electromagnetic

fields, altered in frequency, phase, or other physical properties. Such materials that

are able to manipulate photonic signals efficiently are of importance in optical

communication, optical computing, and dynamic image processing [7-11]. In this

connection transition metal complexes have emerged as potential building blocks

for nonlinear optical materials due to the various excited states present in these

systems as well as due to their ability to tailor metal-organic-ligand interactions

[12-17]. Compared to the more common organic molecules, the metal complexes

offer a large variety of novel structures, the possibility of enhanced thermal

stability, and a diversity of tunable electronic behaviors by virtue of the coordinated

metal center and hence they may find use as NLO materials with unique magnetic

and electrochemical properties [18-20]. The investigations on NLO properties of

metal complexes are being pursued by several research groups [21-27]. It has been

5

reported by Di Bella and co-workers that bis (salicylaldiminato) metal Schiff base

complexes exhibit good second order NLO properties [28-34].

1.1.1.3 In electrochemical sensors

Schiff bases have been used as carriers in the preparation of potentiometric

sensors for determining cations and anions [35-44]. A ruthenium(III) Schiff base

complex was used in the fabrication of chloride PVC-based membrane sensor [45].

The sensor with a composition of 30 % PVC, 62 % benzyl acetate, 5 %

ruthenium(III) Schiff base complex and 3 % hexadecyltrimethyl ammonium

bromide displays near-Nernstian behavior over a wide concentration range. It

shows high selectivity towards chloride ions over several organic and inorganic

anions and was successfully applied for the determination of chloride in serum

samples. It could also be used as an indicator electrode in the potentiometric

titration of chloride ions with silver nitrate solution. Gupta et al. recently reported a

potentiometric aluminium sensor based on the use N, N’-bis (salicylidene)-1, 2-

cyclohexanediamine as a neutral carrier in poly (vinyl chloride) matrix [46]. It was

successfully applied for direct determination of aluminium(III) in biological,

industrial and environmental samples. The electrode could be used in the pH range

of 2.0–9.0 and mixtures containing up to 20 % (v/v) non-aqueous content. It has

been used as an indicator electrode in potentiometric titration of aluminium ion with

EDTA. The Schiff base, N, N′, N″, N′′′-1, 5, 8, 12-tetraazadodecane-bis

(salicylaldiminato), has been used as ionophore for preparing Mn2+

selective sensor

[47]. The sensor was found to be sufficiently selective for Mn2+

over a number of

alkali, alkaline and heavy metal ions and could therefore be used for the

determination of manganese in various samples by direct potentiometry.

6

1.1.1.4 In catalytic activity

Many Schiff base complexes show excellent catalytic activity in various

reactions at high temperature (>100 °C) and in the presence of moisture. The

interest in polymerization of olefins has increased recently due to the observed

catalytic activity of Schiff base complexes in synthesis of commercially important

branched [48, 49] and linear polyethylene [50-53]. The ring opening polymerization

of cycloalkenes with transition metals such as tungsten, molybdenum and

ruthenium in the presence of alkylation agents such as R4Sn or RAlCl2 is possible at

high temperature without any control on molecular weight of polymers. But Schiff

base complex catalyzed ring opening polymerization of cycloalkenes at low

temperature provided a control on the molecular weight of the polymers [54]

without any side reaction. The ring opening of large cycloalkanes is usually a

difficult process but Schiff base complexes of cobalt(II) [55] and chromium(III)

were effective in these reactions with significant enantioselectivity. Phosphine

substitution in N-heterocyclic carbene Schiff base ligand has enhanced ring closing

metathesis reaction to synthesize functionalized olefins [56]. Schiff base complexes

showed significant applications in reduction of ketones to alcohols [57] and

alkylation of allylic substrates [58, 59]. The phosphine Schiff base complexes also

showed improved enantioselectivity in hydrosilation reactions [60]. The chiral

Schiff base complexes of salen [61] and binaphthyl were used as efficient catalysts

in Michael addition reaction. Although the heteroannulation reaction is reported

using transition metal complexes [62, 63] a new catalytic route for annulation

reaction using Schiff base complexes has been an area of current research [64].

Schiff base complexes showed catalytic activity in carbonylation of alcohols and

7

alkenes at low pressure to produce α-arylpropionic acid and their esters [65, 66],

which are used as non-steroidal anti-inflammatory drugs. In addition to

monometallic, the bimetallic Schiff base complexes also showed catalytic activity

in carbonylation reactions [67]. The Heck reaction, an industrially useful process to

synthesize fine chemicals and pharmaceutical, was successfully catalyzed using

Schiff base complexes [68-70]. The complexes of nickel(II) and copper(II) ions

have increased enantioselectivity in alkylation of enolates [71-74]. The

enantiomeric synthesis of aziridines and amides with chiral metalolloporphyrins

was moderate [75-76] but improved in the presence of Schiff base complexes of

copper(II) and manganese(III) [77]. The isomerization of norbornadiene to

quadricyclane was significantly catalyzed using diimine complexes of rhodium

[78]. These interconversions were useful for the storage of solar energy. The

aluminium–salen Schiff base complexes were also used in catalyzing the addition

of hydrogen cyanide to N-allylbenzaldimine, which showed significant

enantiomeric excess [79]. The enantioselectivity in the cyclopropanation reactions

was modest; hence, attempts were also made to improve enantioselectivity in the

cyclopropanation reactions using Schiff base complexes as catalysts [80-81]. The

optically active cyanohydrins are widely used in the synthesis of drugs and

pesticide. These cyanohydrins were synthesized successfully reacting trimethyl

silylcyanide (TMSCN) with aldehydes in the presence of Schiff base complexes of

transition metal ions [82]. Schiff base complexes also played a significant role in

desymmetrization of meso compounds with significant yield and enantiomeric

excess [83]. The homogeneous chiral lanthanum(III) Schiff base complexes showed

8

catalytic activity in asymmetric Diels–Alder reactions [84] and product yield and

enantioselectivity were influenced by the nature of catalysts [85].

1.1.1.5 As corrosion inhibitor

Aggressive acid solutions are widely used for industrial purposes, and

inhibitors are commonly used to control metal dissolution as well as consumption.

Most acid inhibitors are organic compounds containing oxygen, nitrogen and/ or

sulphur [86-90]. Acid inhibitors have many important roles in the industrial field as

components in pre-treatment composition, cleaning solutions and in acidisation of

oil wells. Compounds with functional groups containing hetero-atoms, which can

donate lone pairs of electrons are found to be particularly useful as inhibitors of

metal corrosion [91, 92]. In Schiff bases the condensation product of an amine and

ketone or aldehyde with general formula of R2C=NR is well-known organic

inhibitors [93-94]. Some research work revealed that the inhibition efficiency of

Schiff bases is much greater than that of corresponding amines and aldehydes and

attributed this to the presence of an –HC=N– group in the molecules [95]. The

action of such inhibitors depends on the specific interaction between the functional

groups and the metal surface. So it is very important to clarify the interactions

between inhibitor molecules and metal surfaces in order to search new and efficient

corrosion inhibitors. The main results showed that some mechanical properties

depend on the electronic and structural properties of the inhibitor molecule such as

aromatic and functional groups, electron density on donor atoms and k orbital

character of donating electrons.

9

1.1.1.6 In medicinal chemistry

The treatment of a variety of cancers by cisplatin, cis-[Pt(NH3)2Cl2], has

investigated the on-going investigations of alternative metal-based drugs. The initial

discovery of the anti-tumor activity of platinum complexes was made by Barnett

Rosenberg’s [96] research group in the 1960’s. They were studying the effects of an

electric current passed over platinum electrodes immersed in a solution containing

Escherichia coli cells that were growing in the presence of an ammonium chloride

buffer. Interesting enough was that cell growth continued but division of the cells

was greatly inhibited. It was found from tests that the platinum had reacted with

NH4Cl to form an active compound, cis-[Pt(NH3)2Cl2] (cisplatin) of which the

synthesis and structure were well known from time to time. Tests were done on

cisplatin proving that it has beneficial effects on the treatment of cancer [97]. The

biological activity results from binding to the DNA, thus inhibiting replication.

Today, cisplatin is used in combination with other anticancer agents and is effective

against testicular and ovarian carcinomas, bladder cancer and tumors of the head

and neck.

Anti-cancer drugs have many side effects, like renal toxicity for cisplatin,

which then restrict them to limited doses. Damage to bone marrow causes anemia,

which is an inability to fight infections and a tendency to internal bleeding. Other

side effects include vomiting, diarrhea, nausea, hair loss and neurological

complications. Another drawback that can be encountered in using drugs is the fact

that the tumor can develop resistance to other drugs after the first administration.

10

Copper is a physiologically important metal element that plays an important

role in the endogenous oxidative DNA damage associated with aging and cancer

[98]. Among the copper complexes explored so far, attention has been mainly

focused on the copper(II) complexes of 1,10-phenanthroline ligand due to their high

nucleolytic efficiency [99] and numerous biological activities such as antitumor

[100], anti-candida [101],and antimicrobial [102,103] activities, etc., These

complexes have also been widely utilized as foot printing agents of both proteins and

DNA [104], probes of the dimensions of the minor groove of duplex structures [105],

and identifiers of transcription start sites [106]. Recently, it has been reported that a

binuclear copper(II) complex containing 1, 10-phenanthroline and a trinuclear

copper(II) complex containing di-(2-picolyl) amine bind strongly with DNA and

cleave more effectively than their corresponding monomeric complexes [107-110].

The bis-(phen)copper complex is proposed to bind to DNA by partial intercalation of

one phenanthroline ring, while the other makes favorable contacts in the minor

groove [111]. The reports by Burrows et al. [112] advocate design studies on metal

complexes with nitrogen-donor ligands that can participate in both hydrogen bonding

and interactions for molecular recognition and crystal engineering applications.

Copper chemistry

Copper is one of the most abundant metals in the earth’s crust and it has

been known for many centuries. The word copper is derived from Cyprus where

many ancient copper objects were discovered. It can be found in its pure state and

was probably the first metal from which useful articles were made. Copper is an

important trace element in almost all forms of life and it is the third most abundant

element in the human body following iron and zinc.

11

Copper (II) oxidation state

The copper(II) oxidation state is by far the most common for copper.

Copper(II) complexes have an outer electronic configuration of [Ar] 3d9 4s

0, are

paramagnetic, and are mostly blue or green in color. The coordination number for

copper(II) complexes are usually four, five, and six, with tetrahedral, square planar,

trigonal bipyramidal and octahedral structures commonly found. Electronic spectra

of simple copper(II) complexes contain broad absorption bands in the region of

900-625 nm. Because of the distortion of the octahedral geometry the crystal field is

split, and thus the electronic bands are very difficult to assign in ambiguously. The

theoretical spin-only values for copper(II) lies between 1.75-2.20 B.M are obtained

experimentally [113]. Regardless of temperature (except at extremely low values)

those compounds with geometries approaching octahedral have moments at the

lower end, and those with tetrahedral geometry have values at the higher end.

Medicinal properties of copper compounds

An average adult has 1.4-2.1 mg of copper per Kg of body weight. Copper

is required in the body for hemoglobin synthesis, growth, keratinisation,

pigmentation, bone formation, reproduction, fertility, development and sightedness.

These roles of copper are based upon the requirement of coordinated copper at the

active site of the following copper-dependent enzymes: ceruloplasmin, tyrosinase,

lysyl oxidase, ceramide galactosyl transferase; cytochrome-c-oxidase, dopamine-β-

hydrolyse, pyridoxal requiring monoamine oxidases and a superoxide dismutase.

The use of a copper coil as an intrauterine device to regulate fertility has

been common for many years. Osterberg pointed out that this method of

12

contraception prefers many advantage over oral ones, more efficient contraception

resulting in fewer pregnancies, and greater tolerance, as shown by less pain,

bleeding, spontaneous expulsion and infection. The copper device may have

another advantage over the plain one in that the gonococcidal action of copper may

prevent the spread of gonorrheal infection to the uterus. The mechanism of this anti-

fertility effect is not well established, however , it is likely that copper complexes

formed by the reaction of the uterine contents with either Cu(I) or Cu(II) leached

from the metallic copper coil by endometrial fluids, are absorbed and induce a urine

state of pseudo pregnancy[114].

In the 1920’s it was recognized that the incidence of tuberculosis was much

less in copper miners than in the general population. This led to the successful use

of copper oxide in the treatment of tuberculosis before 1940. Several additional

copper complexes were reported to have antitubercular activity and the complex

sodium 3-(allylcuprothiouredo)-1-benxoate (Fig) was suggested to be more potent

than gold as therapy for tuberculosis [114].

Figure 1.1.1.1 The anti tubercular complex sodium 3--(allylcuprothiouredo)-1-

benxoate.

It is well known that copper(II) complexes of inactive ligands and anti-

inflammatory organic drugs are generally more active than the free ligands or organic

drugs themselves [115]. The most widely used anti-inflammatory drugs are carboxylic

13

acids. For example, salicylic acid and its derivatives have been used for the treatment of

inflammatory diseases for many years. It has been suggested that the biological activity

of acetylsalicylic acid (aspirin) is due to its ability to form metal complexes, and that

the active form of this drugs was, in fact, a copper complex, formed in vivo. The

synthesized copper(II) complex of aspirin (Cu2(O2CC6H4OCOCH3)4] [116] has been

found to be more effective than aspirin itself as an anti-inflammatory agent. In addition,

the copper complex also has antiulcer activity, which further distinguishes it from

aspirin which itself is ulcerogenic. [Cu2(O2CC6H4OCOCH3)4] has been found to be

effective in the treatment of rheumatoid disorders, and it reduces seizures and decreases

tumor growth. The pyridine adduct [Cu2(O2CC6H4OCOCH3)4(C5H5N) 2] has also been

found to be an effective anti-inflammatory, anticancer and anticonvulsant agent [117].

Figure 1.1.1.2 (a) Acetylsalicylic acid (aspirin); (b) structure of

[Cu2(O2CC6H4OCOCH3)4].

The potential of copper carboxylates as pharmacologic compounds has

prompted research into their physico-chemical properties. In 1984, Greenaway et

al., [117] structurally characterized the mononuclear copper(II) bis (pyridine)

acetylaceta complex [Cu2(O2CC6H4OCOCH3)4(C5H5N)2] which has been found to

be an effective anti-inflammatory, anticancer and anticonvulsant agent [116].

14

Nickel complexes draw much attention due to the environmental toxicity

and carcinogenic nature of certain nickel compounds and the chemotherapeutic

properties of other group VIII metal complexes [117]. Some researchers have

shown that bound proteins or synthetic ligands may increase the toxic effect of

nickel ions. However, till now, the exact mechanism to involve carcinogenesis has

not been fully elucidated [118]. The elucidation of the mechanism is essential not

only for the risk assessment [119], but also for developing novel nickel complexes

that have potential applications in medicine and research, such as inhibitors of

cancer proliferation and useful DNA or RNA probes [120, 121]. Therefore, further

studies by employing various ligands with different structures to evaluate and

understand those factors that can determine the DNA binding modes and cleavage

mechanism are necessary. Schiff base complexes present suitable biometric

properties that can mimic the structural features of the active sites, and they have

been widely used in various fields such as illness treatment, biochemical reaction

and biological regulator [122]. Muller et al., systematically investigated ligand

effects, such as ring size, redox potential, ligand donor strength and conformational

flexibility of tetraazamacrocyclic nickel(II) complexes on their DNA cleavage

abilities [117]. Such studies may define the important criteria for design of nickel-

based reagents as structural probes of nucleic acid. It has been widely reported that

the interaction between metal complexes and DNA, such as electrostatic interaction,

intercalative binding, and groove binding, may have great effects on the DNA

cleavage activities of the metal complexes. Systematic investigation of these factors

on the DNA cleavage activities of tetraazamacrocyclic Schiff base nickel(II)

15

complexes may supplement important information for design of nickel base DNA

probes.

Manganese, an essential element for human, is widely distributed in nature and

is second in terms of its terrestial abundance among the first row transition metals

[123]. In biosystem several enzymes namely superoxide dismutase (SOD) [124],

oxalate oxidase [125], lipoxygenase (LO) [126], catalase [127] etc. require manganese

as cofactor for their catalytic activities. In biological reactions manganese sometime

acts as a Lewis acid, on the other hand, it could participate in redox reactions by

flipping its +2, +3 and +4 oxidation states. Hence it has plural roles in biosystem.

However, the role of manganese in oxygen evolving complex (OEC) of photosystem-II

(PSII) is unique [128]. Coordination chemistry of manganese has been exploited for the

structural and functional modeling of metalloprotein e.g. mimicking of OEC in PSII

[129]. Other applications are catalytic activity studies [130] and synthesis of

photolabile metal nitrosyl complexes [131]. Stabilization of manganese oxidation states

has been implicated in manganese toxicity [132]. However, the curiosity originated

from the great demand of manganese chemistry with ligands having phenolato donors

for the mimicking of SOD activity. Moreover, it has been documented in the literature

that native SOD as well as small molecule SOD mimics exhibit nuclease activity

[133, 134]. Hence the researcher was also interested to study DNA interaction as well

as nuclease activity studies.

Cobalt complexes have shown anti-malarial effects [135] where they target

the plasmodium parasite. The activity of the compounds was comparable to that of

the currently used drug, amodiaquine, at similar concentrations. These studies were

in vitro studies and only show the toxicity to the parasite not the host. No further

16

biological testing information was reported. Other studies have shown cobalt

complexes to have anti-bacterial activity which is also comparable to the presently

available drug, imipenium [136]. These results were also done in vitro and there is

no mention of further biological testing on these compounds. Cobalt is a redox

active metal where the +2 and +3 oxidation states are most common.

17

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27

1.2 LITERATURE SURVEY

Parimala et al1, have synthesized a new binucleating ligands L [L- N’-R-

bis(methyl-N-(2-pyridinyl)ketoacetamide] where R-ethylene,1,3-propylene, o-phenylene

were prepared by the condensation of 1 equivalents of methyl-N-(2-

pyridinyl)ketoacetamide with the diamines. The binuclear copper(II) complexes of the

type [Cu2L]X4 where X=ClO4–

and [Cu2LX2]X2 where X=Cl- and Br

- were synthesized

by refluxing the ligand with 2 equivalents of Cu(II) salts. Conductivity studies

showed a1:4 electrolytes for perchlorate complexes and a 1:2 electrolyte for chloro

and bromo complexes. Room temperature magnetic studies gave moment for the

complexes in the range 1.08 to1.4 B.M which are less than 1.73 B.M for d9 system.

This shows that there is antiferromagnetic coupling between the two copper centers.

ESR spectra of the complexes show a broad band which is centered at 2299 G and

the g values obtained were in the range 2.09 to 2.14. Electrochemical studies show

a quasi-reversible two electron reduction occurring at the negative potential in the

range -0.25 to 0.7 V. The initial rate constant for the oxidation of catechol to

o-quinone by the complexes are in the range 1.504×10–1

to 3.83 × 10 –1

min-1

.

Fig. 1.2.1.

28

Rajavel2

have synthesized novel binuclear Schiff base metal complexes

derived from 2-aminobenzaldehyde. The synthesized ligand and its complexes were

characterized by physico-chemical methods. The weak anti-ferromagnetic

interactions between two metal centers were proved by magnetic studies.

Fig. 1.2.2.

Williams et al3, have reported a novel ligand derived from salicyaldehyde and

the synthesized ligand, complexes were characterized by various physic-chemical

methods. These compounds induced convulsions, urination and defecation in mice.

Due to the relatively very low toxicity of complexes, its mode of action was

explored. Its proconvulsant action may possibly involve an interaction of

undissociated complex with muscarinic receptors, and is reversed by atropine.

Fig. 1.2.3

29

Saglam et al4, have synthesized a novel homodinuclear Cu(II) complexes

with a novel oxime-type ligand have been prepared and their nucleolytic activities

on pCYTEXP were established by neutral agarose gel electrophoresis. The analyses

of the cleavage products obtained electrophoretically indicate that although the

examined complexes induce very similar conformational changes on super coiled

DNA by converting super coiled form to nicked form than linear form in a

sequential manner as the complex concentration or reaction period is increased.

Metal complex induced DNA cleavage was also tested for inhibition by various

radical scavengers as superoxide dismutase (SOD), azide, thiourea and potassium

iodide. The antioxidants inhibited the nucleolytic activities of the oxime complexes

but SOD afforded no protection indicating that the nucleolytic mechanism involves

of copper and/ or manganese complex-mediated reactive oxygen species such as

hydroxyl radicals being responsible for the oxidative DNA cleavage.

Fig. 1.2.4

Sengottuvelan et al5, have synthesized a new series of binuclear

unsymmetrical compartmental oxime complexes using mononuclear complex [ML]

30

(L=/1, 4-bis [2-hydroxy-3-(formyl)-5-methylbenzyl] piperazine), hydroxylamine

hydrochloride and triethylamine. In this system there are two different

compartments, one has piperazinyl nitrogen’s and phenolic oxygen’s and the other

compartment has two oxime nitrogen’s and phenolic oxygens as coordinating sites.

The complexes were characterized by elemental and spectral analysis.

Electrochemical studies of the complexes show two step single electron quasi-

reversible redox processes at cathodic potential region. For copper complexes

E1pc/0.18 to to/0.62 and E

2pc 1.18 to1.25 V, for nickel complexes E

1pc 0.40 to 0.63

and E2pc1.08 to 1.10 V and reduction potentials are sensitive towards the chemical

environment around the copper and nickel atoms. The nickel(II) complexes undergo

two electrons oxidation. The first one electron oxidation is observed around _/

0.75 V

and the second around _1.13 V. ESR Spectra of the binuclear copper(II) complexes

[Cu2L](ClO4), [Cu2L(Cl)], [Cu2L(NO3)] shows a broad signal at g=2.1 indicating

the presence of coupling between the two copper centers. Copper(II) complexes

show a magnetic moment value of µeff around 1.59 B.M at 298 K and variable

temperature magnetic measurements show a _/2 J value of 172 cm

-1 indicating

presence of anti-ferromagnetic exchange interaction between copper(II) centers.

Fig 1.2.5

31

Tuna et al

6, have reported synthesis of ligand derived from 3-formyl-salicylic

acid, 3-[N-2-(pyridylethyl) formimidoyl] salicylic acid. The synthesis of ligand and

metal complexes were characterized by elemental analysis, molar conductance, UV,

IR, NMR and magnetic studies. The interactions between two metal centers were

proved by magnetic studies.

Fig. 1.2.6.

Srinivasan et al7, have synthesized a bimetallic nickel(II) complex with the

ligand Hsalamp (2-[(4-methylpyridin-2-ylimino)-methyl]-phenol), having the

molecular formula, Ni2C26H22 N4O10Cl2, is synthesized and characterized by

elemental, UV-Vis, IR and EPR studies. The IR spectrum confirms the presence of

coordinated perchlorate ion and the UV-Vis. spectrum substantiates that the

geometry around the metal ion is distorted square pyramidal. In the solvent

methanol, the complex undergoes dissociation indicating the nature of the complex

to be 1: 2 electrolytes. The single crystal EPR studies indicate that the zero-field

splitting is not large and the spectra can be observed even at room temperature, not

so common for a nickel(II) ion. The spin Hamiltonian parameters calculated from

single crystal rotations are: g – 2.377, 2.219, 2.071 and D – 9.7, 4.2 and – 13.9 mT.

32

Optical and electron paramagnetic spectral data have been used to obtain the

parameters Dq, B and C.

Fig. 1.2.7

Bera et al8, have synthesized the low-temperature stoichiometric Schiff base

reaction in air in 3:1 mole ratio between benzaldehyde and triethylenetetramine

(trien) in methanol yields a novel tetraaza m-bis(bidentate) acyclic ligand L. It was

characterized by elemental analysis, IR, EI mass and NMR (1H and

13C) spectra.

The formation of a five-membered imidazolidine ring from the ethylenediamine

backbone as a spacer-cum bridging unit gives rise to a new type of imidazolidine-

bridged ligand. A geometric optimization was made of the synthesized ligand and

its complexes by the method of molecular mechanics (MM2) method in order to

establish the stable conformations. This hitherto unknown tetraaza acyclic ligand

affords new cationic dicopper(I/ I) and dicopper(II/ II) complexes in good yield.

Dicopper(II/ II) complex displays weak d–d transition bands in the visible region,

while dicopper(I/ I) complex displays strong MLCT band in the same region. Both

the dinuclear complexes are of non-intimate nature and show interesting solution

electrochemical behavior. EPR spectral study of m-bis (imidazolidino) bridged

dicopper(II/ II) complex also supports the non-communicative nature of the two

copper centers within the same molecule.

33

Fig. 1.2.8

Karabocek et al9, have reported a new ligand incorporating a dioxime

moiety, (2E, 3E)-3-[(2-{[(1E, 2E)-2-(hydroxyimino)-1-methylpropylidene] amino}

phenyl)imino] butan-2-one oxime, (H2Phmdo) (3) has been prepared by

reacting 2,3-butanedionemono-{O-[4-(1-methyl-2-oxo-propylideneaminooxy)-

2, 3-bis-(1-methyl-2-oxo-propylideneaminooxy-methyl)-but-2-enyl]-oxime} (2)

with 1, 2-phenylenediamine.

Fig. 1.2.9

Karabocek et al10

, synthesized a new dioxime ligand, derived from butane

monoxime. The dioxime ligand and its copper(II) complexes were characterized by

1H-NMR,

13C-NMR, and elemental analyses, magnetic moments, IR and mass

spectral studies. Elemental analyses, stoichiometric and spectroscopic data of the

metal complexes indicated that the metal ions are coordinated to the oxime and

imine nitrogen atoms (>C=N). In the dinuclear complexes, in which the first Cu(II)

ion was complexed with nitrogen atoms of the oxime and imine groups, the second

34

Cu(II) ion is ligated with dianionic oxygen atoms of the oxime groups and is linked

to the 1, 10-phenanthroline nitrogen atoms. The trinuclear copper(II) complex (6)

was formed by coordination of the third Cu(II) ion with dianionic oxygen atoms of

each of two molecules of the mononuclear copper(II) complexes.

Fig. 1.2.10

Salem et al11

, have been reported synthesis of ligand derived from diacetyl

monoxime aroylhydrazones. The synthesized complexes have been characterized

by various physico chemical methods. In these complexes the oximate group

functions as a bridge between the two nickel(II) ions.

Fig. 1.2.11

35

Tumer et al12

, have been synthesized the amine compound

2-(2-aminoethyliminomethyl) phenol (H3A) as the starting material, and then they

prepared the polydentate Schiff base ligands from the reactions of the amine

compound (H3A) with phthalaldehyde (H2L), 4-methyl-2, 6-di-formlyphenol (H3L1)

and 4-t-butyl-2, 6-di-formylphenol (H3L2) in the ethanol solution. Moreover, the

complexes Cd(II), Cu(II), Co(II), Ni(II), Zn(II) and Sn(II) of the ligands H2L, H3L1

and H3L2 have been prepared. All compounds have been characterized by the

analytical and spectroscopic methods. In addition, the magnetic susceptibility and

molar conductance measurements have been made. The catalytic properties of the

mono- and binuclear Co(II) and Cu(II) complexes have been studied on the 3,5-di-

tert-butylcatechol (3, 5-DTBC) and ascorbic acid (aa) as a substrate. The oxidative

C–C coupling properties of the Co(II) and Cu(II) complexes have been investigated

on the sterically hindered 2, 6-di-tert-butylphenol (dtbp). The antimicrobial activity

properties of the ligands and their mono- and binuclear complexes have been studied

against the bacteria and fungi. The results were compared to the antibacterial and

fungi drugs. The TGA curves show that the decomposition takes place in three steps

for all complexes. Electrochemical properties of the complexes Cu(II) and Ni(II)

were investigated for the first time in acetonitrile by cyclic voltammetry.

Fig. 1.2.12

36

Shebl 13

have been synthesized the tetradentate N2O2 donor Schiff base ligand

by the condensation of 4, 6-diacetylresorcinol with benzyl amine. The structure of

the ligand was elucidated by elemental analyses, IR, 1H NMR, electronic and mass

spectra. Reaction of the Schiff base ligand with nickel(II), cobalt(II), iron(III),

cerium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded binuclear

metal complexes. Also, reaction of the ligand with several copper(II) salts,

including Cl−, NO3

−, AcO

−, ClO4

− and SO4

2− afforded different metal complexes

that reflect the non-coordinating or weakly coordinating power of the ClO4− anion

as compared to the strongly coordinating power of SO4 2−

and Cl− anions.

Characterization and structure elucidation of the prepared complexes were achieved

by elemental and thermal analyses, IR, 1H NMR, electronic, mass and ESR spectra

as well as magnetic susceptibility measurements. The metal complexes exhibited

different geometrical arrangements such as square planar, octahedral, square

pyramidal and pentagonal bipyramidal arrangements. The variety in the geometrical

arrangements depends on the nature of both the anion and the metal ion.

Fig. 1.2.13

Emara et al14

, have reported the bifunctional carbonyl compound;

4, 6-diacetyl resorcinol (DAR) serves as precursor for the formation of different

Schiff base ligands, which are either di- or tetra-basic with two symmetrical sets of

either O2N or N2O tridentate chelating sites. The condensation of 4, 6-

37

diacetylresorcinol with 3-amino-1-propanol (3-AP) or 1, 3-diaminopropane (DAP),

yields the corresponding hexadentate Schiff base ligands, abbreviated as H4La and

H2Lb, respectively. The structures of these ligands were elucidated by elemental

analyses, IR, mass, 1H NMR and electronic spectra. Reaction of the Schiff base

ligands with copper(II), nickel(II), cobalt(II), zinc(II), cadmium(II), iron(III),

chromium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded the

corresponding transition metal complexes. A variety of binuclear complexes for the

metal complexes were obtained with the ligands in its di- or tetra-deprotonated

forms. The structures of the newly prepared complexes were identified by elemental

analyses, infrared, electronic, mass, 1H NMR and ESR spectra as well as magnetic

susceptibility measurements and thermal gravimetric analysis (TGA). The bonding

sites are the azomethine and amino nitrogen atoms, phenolic and alcoholic oxygen

atoms. The metal complexes exhibit different geometrical arrangements such as

square planar, tetrahedral, square pyramid and octahedral arrangement.

Fig. 1.2.14

Annigeri et al15

, have synthesized a novel binuclear cobalt(II), nickel(II),

copper(II) and zinc(II) complexes of general composition [M2L(µ-Cl)Cl2].nH2O

with the Schiff-base ligand (where is the potential pentadentate ligands derived by

condensing 2, 6-diformyl-4-methylphenol with 4-amino-3-antipyrine) have been

38

synthesized and characterized. Analytical and spectral studies support the above

formulation. 1H-NMR and IR spectra of the complexes suggest that they have an

endogenous phenoxide bridge, with chloride as the exogenous bridge atom. The

electronic spectra of all the complexes are well characterized by broad d–d and a

high intensity charge-transfer transitions. The complexes are chloro-bridged as

evidenced by two intense far-IR bands centered around 270–280 cm-1

. Magnetic

susceptibility measurements show that complexes are antiferromagnetic in nature.

The compounds show significant growth inhibitory activity against fungi

Aspergillus niger and Candida albicans and moderate activity against bacteria

Bacillus cirroflagellosus and Pseudomonas auresenosa.

Fig. 1.2.15

Wang et al16

, have reported a new bis tridentate ligand 2,2’-bipyridine-3, 3’-

[2-pyridinecarboxamide] which can bind transition metal ions has been synthesized

via the condensation of 3, 3’-diamino-2, 2’-bipyridine together with 2-pyridine

carbonyl chloride. Two copper(II) coordination compounds have been prepared and

characterized: In the coordination geometry around both CuII ions is best described

as distorted trigonal bipyramidal where the remaining two coordination sites are

39

satisfied by hexafluoroacetylacetonate counter ions. The magnetic susceptibility

data for ligand (2-270 °K), reveal the occurrence of weak anti-ferromagnetic

interactions between the CuII ions.

Fig. 1.2.16

Krishnapriya et al17

, have reported a new ligand N, N-bis{3-(2-formyl-4-

methyl-phenol)-6-iminopropyl}oxamide (L) and its mono- and binuclear copper(II)

complexes have been synthesized and characterized. The ligand shows absorption

maxima at 249 and 360 with a weak transition at 455 nm. The ligand was found to be

fluorescent and shows an emission maximum at 516 nm on excitation at 360 nm. The

electronic spectra of the mono- and binuclear Cu(II) complexes exhibited a d–d

transition in the region 520–560 nm characteristic of square planar geometry around

Cu(II) ion. The ESR spectrum of the mononuclear complex showed four lines with

nuclear hyperfine splitting. The binuclear complex showed a broad ESR spectrum

with g = 2.10 due to anti-ferromagnetic interaction between the two Cu(II) ions. The

room-temperature magnetic moment values (μeff) for the mono- and binuclear Cu(II)

complexes are found to be 1.70 μB and 1.45 μB, respectively. The electrochemical

studies of the mononuclear Cu(II) complex showed a single irreversible one-electron

wave at −0.70V (Epc) and the binuclear Cu(II) complex showed two irreversible one-

electron reduction waves at −0.75V (E1pc) and −1.27V (E2pc) in the cathodic region.

40

Fig. 1.2.17

Seena et al18

, have reported five oxovanadium(IV) complexes of 2-hydroxy-

4-methoxybenzaldehyde nicotinic acid hydrazone (H2L1), 2-hydroxy-4-

methoxyacetophenone nicotinic acid hydrazone (H2L2) and a binuclear

oxovanadium(V) complex of H2L2 have been synthesized. These complexes were

characterized by different physicochemical techniques like electronic, infrared and

EPR spectral studies. The complexes [VOL1]2.H2O (1) and [VOL

2]2 .H2O (4) are

binuclear and [VOL1bipy] (2), [VOL

1phen] .1.5H2O (3) and [VOL2phen] .2H2O (6)

are heterocyclic base adducts and are EPR active. In frozen DMF at 77 K, all the

oxovanadium(IV) complexes show axial anisotropy with two sets of eight line

patterns. The complex [VOL2.OCH3]2 (5) is an unusual product and has distorted

octahedral geometry, as obtained by X-ray diffraction studies.

Fig. 1.2.18

41

Kiani et al19

, have synthesized the ligand derived from tetramethylfuranone,

and TMFPreH (TMFPreH=4-[3-(4-hydroxyimino-2, 2, 5, 5-dimethyl-dihydrofuran-

3-ylideneamino)-propylimino]-2, 2, 5, 5-tetramethyl-dihydrofuran-3(2H)-one

oxime) and its Cu(II) and Ni(II) complexes.

Fig. 1.2.19

Dede et al20

, have reported a new series of homo- and heteropolynuclear

copper(II) complexes of N,N″-bis[1-biphenyl-2-hydroxyimino-2-(4-acetylanilino)-

1-ethylidene]-diamines have been prepared and characterized by different

physical techniques. The starting point of the research was the reaction

of chloroacetyl chloride with biphenyl in the presence of aluminum

chloride. 4-biphenylhydroximoyl chloride was obtained by reacting

synthesized 4-(chloroacetyl) biphenyl with alkyl nitrite. Substituted

4-(alkylaminoisonitrosoacetyl) biphenyl (ketooxime) was prepared by reacting

4-biphenylhydroximoyl chloride with 4-aminoacetophenone in ethanol. Homodi-,

homotrinuclear and heterodinuclear copper(II) perchlorate complexes of

tetradentate Schiff bases which possess N4 donor sets derived from the

condensation of 4-(arylaminoisonitrosoacetyl)biphenyl and diamine derivatives

were synthesized and characterized. Elemental analysis, FT–IR, ESR, molar

conductivity, magnetic moment measurements and thermal analyses studies were

42

utilized for the investigation of the complexes. The free ligands were also

characterized by 1H- and

13C-NMR spectra. Elemental analyses, stoichiometric and

spectroscopic data of the metal complexes indicated that the metal: ligand ratio of

dinuclear copper(II) complexes were found to be 2 : 1 while this ratio was 3 : 2 in

trinuclear copper(II) complexes and the metal complexes indicated that the metal

ions are coordinated to the oxime and imine nitrogen atoms. The extraction abilities

of the novel ligands were also evaluated in chloroform by using several transition

metal picrates such as Mn2+

, Co2+

, Ni2+

, Cu2+

, Zn2+

, Pb2+

, Cd2+

, Hg2+

. It has been

observed that both ligands show a high affinity to Cu2+

ions.

Fig. 1.2.20

Jia et al21

, have reported the synthesis of three novel ternary copper(II)

complexes, [Cu2(phen)2(L-PDIAla)(H2O)2](ClO4)20.5H2O(1),Cu4(phen)6(D,L-

PDIAla)(H2O)2] (ClO4)6 3H2O (2) and [Cu2(phen)2(D,L-PDIAla)

(H2O)](ClO4)25H2O(3) (phen = 1,10-phenanthroline, H2PDIAla = N,N’-(p-

xylylene) di-alanine acid) have been synthesized and structurally characterized by

single-crystal X-ray crystallography and other structural analysis.

43

Fig. 1.2.21

Shebl et al22

, have reported the condensation of O-acetoacetylphenol and

1,2-diaminopropane in 1:1 molar ratio under condition of high dilution yielded the

mono-condensed dibasic Schiff base ligand with a N2O2 donors. The mono-

condensed ligand has been used for further condensation with 2-hydroxy-5-

nitrobenzaldehyde to obtain the new asymmetrical dicompartmental Schiff base

ligand, with N2O3 donors. The structure of the ligand was elucidated by analytical

and spectroscopic tools (IR, 1H and

13C NMR spectra) which indicated that the

coordinating sites are oxygen atoms of the phenolic OH groups, nitrogen atoms of

the azomethine groups and the oxygen atom of the ketonic group. The structures of

the complexes were characterized by various techniques such as elemental and

thermal analyses, IR, 1H and

13C NMR, mass and electronic spectra as well as

conductivity and magnetic moment measurements. Square-planar and octahedral

geometries are suggested for the Cu(II), Co(II) and Ni(II) complexes, octahedral

geometry for the Fe(III) and VO2+

complexes while uranium(VI) ion is octa-

coordinated in its complex. The Schiff base and its metal complexes were evaluated

for antimicrobial activity against Gram positive bacteria (Staphylococcus aureus),

Gram negative bacteria (Escherichia coli) and fungi (Candida albicans and

Aspergillus flavus). The ligand and some of its complexes were found to be

biologically active.

44

Fig. 1.2.22

Raman et al23

, (2010) have synthesized few novel binuclear Schiff base

metal complexes [M2LCl3], where M= Cu(II) and Zn(II); L=2, 6-bis-({2-[(3-

hydroxy-4-nitrobenzylidene) amino] ethylimino}methyl)-4-methylphenol(BHEM),

2, 6-bis-({2-[(3, 4-dimethoxybenzylidene)amino] ethylimino} methyl)-4-

methylphenol (BDEM) and 2, 6-bis-({2-[(2, 3, 5-richlorobenzylidene) amino]

ethylimino}methyl)-4-methylphenol (BTEM),have been synthesized and

characterized by analytical and spectral data. From the DNA cleavage study of

these complexes, investigated by gel electrophoresis, they found that they

efficiently cleave super coiled pUC19 DNA in the presence of a reducing agent (3-

mercaptopropionic acid) and on irradiation with UV light of 360 nm wavelength.

The mechanism reveals that singlet oxygen (1O2) plays a significant role in the

photo cleavage. The superoxide dismutase (SOD) mimetic activity of the

synthesized complexes demonstrates that most of the complexes have promising

SOD-mimetic activity. The antimicrobial study indicates that the complexes inhibit

the growth of bacteria and fungi more than the free ligands.

45

Fig. 1.2.23

Maity et al

24, have reported synthesis of ligand O-phenylenediamine with

diacetyl monoxime. The synthesized ligand and its metal complexes were

characterized by various physico-chemical methods. The metal centers were

connected via an oxygen-bridged arrangement.

Fig. 1.2.24

El-Hendawy et al25

,

have reported the synthesis of complexes

[M(Hdamsm)2]XH2O (M = Fe, X = NO3; M = Ru, X = Cl), [Ru(Hdamsm)

(PPh3)2X0](X0= Cl, Br), and [VO(Hdamsm)(acac)] (H2damsm =diacetylmonoxime

Schiff base of S-methyldithiocarbazate, Hacac = acetylacetone) have been prepared

and characterized by spectroscopic techniques. Their redox properties were

investigated by cyclic voltammetry. The X-ray crystal structure of

[Fe(Hdamsm)2]NO3.H2O has been determined and shows that the complex has a

46

distorted octahedral geometry in which the Hdamsm behaves as a monoanionic

NNS tridentate ligand coordinating via oxime nitrogen, hydrazinic imine nitrogen,

and thiolate sulfur. The reactivity of these complexes toward oxidation of alcohols

in the presence of t-BuOOH and H2O2 as co-oxidants is reported.

Fig. 1.2.25

Geeta et al26

, have reported a binucleating new Schiff-base ligand with a

phenylene spacer, afforded by the condensation of glycyl–glycine and

o-phthalaldehyde has been served as an octadentate N4O4 ligand in designing some

binuclear complexes of cobalt(II), nickel(II), copper(II), and palladium(II). The

binding manner of the ligand to the metal and the composition and geometry of the

metal complexes were examined by elemental analysis, conductivity measurements,

magnetic moments, IR, 1H,

13C NMR, ESR and electronic spectroscopies, and TGA

measurements. There are two different coordination/ chelation environments

present around two metal centers of each binuclear complex. The composition of

the complexes in the coordination sphere was found to be [M2(L)(H2O)4] (where

M = Co(II) and Ni(II)) and [M2(L)] (where M = Cu(II)and Pd(II)). In the case of

Cu(II) complexes, ESR spectra provided further information to confirm the

binuclear structure and the presence of magnetic interactions. All the above metal

complexes have shown moderate to good antibacterial activity against Gram-

positive and Gram-negative bacteria.

47

Fig. 1.2.26

Budagumpi et al27

, have synthesized Pyrazolyl diazine (-NN) bridged last

first row transition metal(II) complexes have been prepared by the interaction of

metal(II) chlorides with an ‘end-off’ compartmental Schiff base ligand. The ligand

system has a strong diazine bridging component and obtained as a condensation

product between 1Hpyrazole-3, 5-dicarbohydrazide and 3-acetylcoumarin in

absolute ethanol. All synthesized compounds were characterized on the basis of

various spectral and analytical techniques. Complexes are found to be non-

electrolytes and monomeric in nature. The magnetic exchange interactions were

very weak because of the more electronegative exogenous chloride, though diazine

bridging group bring metal centers in a close proximity.

Fig. 1.2.27

48

Prakash Naskar et al28

, have synthesized a novel ligand by the condensation

of an equimolar proportion of diacetyl-monoxime monohydrazone and

1-methylimidazole-2-carboxaldehyde in methanol gives rise to the imidazole

azine, 3-(1-methylimidazol-2-yl) methylenehydrazonobutan-2-one oxime(HL).

Reaction of 1:1stoichiometric proportion of HL with copper(II)perchlorate

hexahydrate in methanol yields a dimeric oximato bridged copper compound,

[Cu2L2(H2O)2](ClO4)2. The compound is characterized by C, H and N analyses,

FT-IR, ESI–MS, conductivity measurement, UV–Vis spectra and X-ray single

crystal diffraction. The geometry around each copper center is distorted square

pyramidal. The copper(II) dimer shows anti-ferromagnetic interaction mediated by

symmetric disposition of oximato groups.

Fig. 1.2.28

49

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51

1.3 SCOPE OF THE PRESENT WORK AND OBJECTIVES

Schiff base metal complexes are an area of increasing interest. Because of

the presence of both hard nitrogen and oxygen soft sulphur atoms in the backbones

of these ligands, they are readily co-ordinate with a wide range of transition metal

ions yielding stable and intensely coloured metal complexes. These complexes have

numerous applications, such as, in the treatment of cancer, as antibactericide agents,

as antivirus agents, as fungicide agents and for other biological properties. The

design and development of potential therapeutic agents, particularly those designed

to target nucleic acids site specifically or to mimic the function of enzymes that

participate in nucleic acid strand cleavage can lead to safer and more rational

approaches to novel therapeutic agents for cancer, viral diseases and tools for

molecular biology. A bimetallic core is versatile at the active site of many

metalloenzymes and plays an essential role in biological systems by the interplay of

a pair of metal ions. The binuclear metal complex has greater cleaving efficiency

than mononuclear complex. For these applications, we are extending this field in

synthesis of novel binuclear Schiff base metal complexes.

The literature survey of the Schiff base complexes derived from

3, 3’diamino benzidine with 2, 3 butanedione monoxime, phthalaldehyde

monoxime and O-hydroxyacetophenone shows that no work has been reported

using these compounds.

The present study describes the synthesis, spectral, characterization, redox,

DNA binding, cleavage and anti-microbial activities of novel Schiff base binuclear

52

metal complexes obtained by the condensation of 3, 3’diaminobenzidine

with 2, 3 butanedione monoxime, phthalaldehyde monoxime and

O-hydroxyacetophenone.

Objectives of the study

1. Synthesis of binuclear Cu(II), Ni(II), Co(II) and Mn(II) Schiff base metal

complexes derived from 3, 3’diaminobenzidine with phthalaldehyde

monoxime, 2, 3 butanedione monoxime, O-hydroxyacetophenone by

conventional methodology as described in the literature.

2. The synthesized compounds are characterized by various physico-chemical

methods such as elemental analysis, molar conductance, IR, UV, NMR,

cyclic voltammetry, thermal, magnetic and EPR studies.

3. The synthesized compounds are screened for their anti-microbial activity

against Gram positive, Gram negative bacteria and fungi by well/ disc

diffusion method.

4. The CT- DNA binding with metal complexes were studied by using

absorption spectra, cyclic voltammetry and viscosity measurements.

5. pBR322-DNA cleavage of metal complexes was performed with Gel

electrophoresis method.