Synthesis, IR and Thermal studies of Ni (II) and Mn (II) Schiff Base Complexes

Project report May-2012

Supervisor Submitted by Prof. A.P.Mishra Brajendra Singh

Kusmariya

Department of Chemistry Dr.Hari Singh Gour Central University, Sagar (M.P.)

• Chapter- I deals with introduction• Chapter- II deals with application of Schiff base metal

complexes• Chapter- III deals with characterization techniques for

studying metal complexes • Chapter- IV deals with experimental work• Chapter- V deals with result and vdiscussion• Chapter-VI deals with significance of Schiff base metal

complexes

Introduction

• Synthesis and characterization of new coordination compounds have always been a challenge to the inorganic chemists.

• Schiff bases have been playing an important part in the development of coordination chemistry.

• Schiff base metal complexes have been studied extensively because of their attractive chemical and physical properties and their wide range of applications in numerous scientific areas.

Schiff Base ligands :-• Schiff’s bases, named after the German chemist Hugo Schiff (1834-1915) • Those compounds having a formula RR'C=NR″ where R is an aryl group, R'

is a hydrogen atom and R″ is either an alkyl or aryl group.• Schiff bases can be prepared by condensing carbonyl compounds and

amines in different conditions and in different solvents with the elimination of water molecules. The presence of a dehydrating agent normally favors the formation of Schiff bases.

• 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.

• When aldehyde is a salicylaldehyde derivative and amine is a diamine derivative, the condensation produces interesting N2O2 Schiff base compounds called salen ligands

Macrocyclic Schiff base have been prepared by well known self condensation reaction of appropriate formyl- or keto- and primary amine precursors and find wide applications in macrocyclic and supramolecular chemistry

Schiff Base as Coordinating Ligands :-

• Schiff base ligands coordinate to a metal through the imine nitrogen and another group, usually oxygen, situated on the original aldehyde.

• Schiff bases are among the most general N ligands, because the basicity of the sp2-hybridized N lone pair, although lower than that of amines (sp3 hybridization), is well suited to form complexes with metal ions.

• the stability of the Schiff base group increases considerably upon coordination with a metal ion and formation of the Schiff base-metal complex.

• For this reason, in contrast to the free ligand, the Schiff base-metal complex can be used in wet solvents or even in aqueous media without undergoing hydrolysis.

Schiff base transition metal complexes :-• Metal complexes are generally prepared by treating metal salts with

Schiff base ligands under suitable experimental conditions. • Cozzi has outlined five synthetic routes that are commonly employed for

the preparation of Schiff base metal complexes and these are depicted as follow-

2. Applications of Schiff base transition metal complexes

2.1 Photophysical Properties:-• Photophysical properties of transition metal complexes help in the design of new

molecules as fluorescent probes for sensing and highly luminescent materials, especially for organic light emitting devices.

• metal complexes are used as photocatalysts, as photosensitizer material in solar energy conversion, in molecular diodes, as chemical sensors or as biosensors, and in supramolecular clusters.

• Schiff base complexes have been studied for their wide applications in various fields such as catalysis, as corrosion inhibitors and in biological field, etc. However, the studies on their optical properties, such as fluorescence, are rare.

• Search on the keyword “Schiff base” in the SciFinder database results in 39894 articles, among them only 209 articles contain the keyword “luminescence”.

2.1.1 Luminescence :-

• Luminescence is an emission of ultraviolet, visible or infrared photons from an electronically excited species.

• Luminescence is formally divided into two categories: fluorescence and phosphorescence depending on the nature of the excited state.

• Fluorescence is emission of light from singlet excited states while Phosphorescence is emission of light from triplet excited states.

• Phosphorescence is usually not seen in fluid solutions at room temperature. • Transition metal–ligand complexes, which contain a metal and one or more

organic ligands, display mix singlet–triplet states. These complexes display intermediate lifetimes of hundreds of nanoseconds to several microseconds.

• This process are represented in the Jablonski diagram .

2.1.2The Importance of the Photoluminescence and Electroluminescence :-

Transition metal complexes are finding broad potential applications in organic light-emitting diodes,light-emitting diodes, light-emitting electrochemical cell, solar cells and sensors due to their desirable optical,electronic and mechanical properties, these compounds play an important role in developing semiconductors and optoelectronic devices.

2.2 Schiff base transition metal complexes in catalysis

• Schiff base complexes play a central role in various homogeneous catalytic reactions and the activity of these complexes varies with the type of ligands, coordination sites and metal ions.

• Literature reports reveal that a large number of Schiff base metal complexes exhibit catalytic activities.

• Chiral Schiff base complexes are more selective in various reactions such as oxidation, hydroxylation, aldol condensation and epoxidation.

2.2.1 Polymerization reaction :- The polymerization reactions are catalyzed with various catalysts and based on

experimental observations Conditions for catalyst :- [1]. Catalyst must have high olefin-insertion ability. [2]. Catalyst must have two available cis-located sites for polymerization [3]. Catalyst must be stable enough under the usual polymermerization conditions. Aluminum complexes of a series of tridentate Schiff base ligands, 1-4, were found

to catalyse the polymerization of ethylene

2.2.2 Oxidation reactions:- Titanium(IV), vanadium(IV), copper(II) or zinc(II) complexes of chiral Schiff base

ligands of –O-N-O- type were used in various asymmetric chemical transformations.

The binuclear palladium Schiff base complex, 5 was found to be effective catalysts in direct oxygenation of unfunctionalized hydrocarbons and phenols . Dinuclear Schiff base complexes of copper (II) ions 6 were used successfully in hydroxylation of phenol

2.2.3 Epoxidation reactions :-• chromium and manganese-salen complexes.are effective catalyst for chiral and

asymmetric epoxidations of alkenes. • Jacobsen’s complex, has been demonstrated to be very effective for the

enantioselective epoxidation of unfunctionalised olefins

2.2.4 Hydrogenation reactions :-• Schiff base complexes of transition metals are efficient catalysts in carrying out

asymmetric reduction of dialkyl ketones.• Schiff base complexes of general formula [RuX(EPh3)(LL’)] where X = Cl or Br,E = P

or As and LL’ = [ONNO] donor of the heterocyclic Schiff base ligands, show catalytic activity in the transfer hydrogenation of aliphatic and aromatic ketones in the presence of isopropanol and KOH.

Decomposition of hydrogen peroxide:-

The decomposition of hydrogen peroxide is an activated process, and the presence of catalysts like Schiff base complexes of transition metal ions was effective in catalyzing the decomposition of hydrogen peroxide.

2.2.6 Diels–Alder reaction :- The first target-oriented synthesis of pyranoquinolines as potential

antibacterial agents by inverse electron demand Diels–Alder reaction (IED-DA) was accomplished using chiral salen–AlCl complex as catalyst,

Chiral Schiff base lanthanum (III) complexes displayed catalytic activity in the asymmetric Diels– Alder reaction of 3-(2-propenoyl)-2-oxazolidinone with cyclopentadiene

2.3. Biological activities of Schiff bases and their metal complexes

In azomethine derivatives, the C=N linkage is essential for biological activity, several azomethines were reported to possess remarkable antibacterial, antifungal, anticancer and diuretic activities. A considerable number of Schiff-base complexes have potential biological interest, being used as more or less successful models of biological compounds.

Antimicrobial Activities :-• The Zn complex showed a wide range of bactericidal activities against the

Gram positive and Gram negative bacteria, were potent than or similar with commercial antibiotics.

• A comparative study of the MIC values for the ligands and their complexes indicates that the complexes exhibit higher antimicrobial activity.

Antitumor Activities :- Metal complexes of Schiff base have been recommended a new line for

search to new antitumor activity A tridentate Schiff base derived from the condensation of S-benzyldithiocarbazate

with salicyldehyde and its Zn, Sb, Cu complexes showed cytotoxic properties.

Synthetic Action on Insecticides :-• Schiff base derived from sulfane thiadizole and salicylaldehyde or thiophene-

2-aldehydes and their complexes show toxicities against insects α- Aminoacid• Flourination on aldehyde part of Schiff base enhances insectocidal activity

Schiff bases and their metal complexes

Plant Growth Regulator :- N-acetylated compounds show growth inhibitory activity with seedling of wheat,

Schiff bases show remarkable activities on plant hormone such as the auxins on root growth Schiff base of ester and carboxylic acid show remarkable activity as plant growth hormone Schiff bases of thiodiazole have good plant growth regulator activity towards auxin and cytokine.

3. Physicochemical methods in the characterization of complexes

A number of techniques are used for characterizing and determining the molecular structure of ligands with their metal complexes, and also for deciding the stereochemistry of complexes. The choice of method depends upon the physical state of the complex. Commonly encountered characterization techniques are:

• Elemental analysis.• Molar conductance.• Infrared absorption spectroscopy (IR). • Nuclear magnetic resonance (NMR). • Electronic spectroscopy (UV-Vis). • Magnetic susceptibility.• Mass spectroscopy. • Electron spin resonance spectroscopy (ESR).• Thermogravimetric analysis (TGA). • X-Ray diffraction (XRD).

IR Spectroscopy :-• IR spectroscopy is most widely used for information about the mode of linkage,

presence of functional group, aromatic ring and sites of attachment of ligand to the metal ion, the nature of coordinate bond and stereochemistry of metal complexes.

• IR spectrum of a ligand after complexation with metal must differ from that of the free ligand.

• The difference between the IR spectra of the free ligand and their coordination compounds may be noted as;

(1) Change in band positions. (2) Change in intensity of relative bands. (3) Splitting of single peak of ligand into several bands in the complexes. (4) Appearance of new bands. (5) Bands may broaden after coordination. (6) Disappearance of band frequency.

Thermal Analyses (TA) :-

• Thermal analyses refer to a group of techniques in which a property of a sample is monitored against time or temperature while the temperature of the sample, in a specified atmosphere, is programmed.

• TG can directly record the loss in weight with time or temperature due to dehydration or decomposition. Thermogravimetric curves are characteristic of a given compound or system becausof the unique sequence of physiochemical reactions which occur over definite temperature ranges .

4. Experimental Work

Materials :-

In preparation of reagents, chemicals of analytical grade purity were used.

Chemicals and solvents used for the preparation of Schiff base ligands and metal complexes are:

Salicylaldehyde, p-Aminoacetophenone, Nickel (II) chloride, Mangenese(II) chloride, Ethanol, Methanol, Chloroform and Diethyl ether

Preparation of Schiff Base (SAP) :- CHO

OH

H2N

COCH3

HC

OH

N COCH3

salicylaldehyde (1.221 g, 0.01mol) p-aminoacetophenone (1.352

g, 0.01mol)

SAP = Salicylidene-4-aminoacetophenone

• Preparation of Metal complexes with Schiff Base (SAP) :-

To a solution of (2.390 g, 0.01mol) Schiff Base SAP in 50 mL MeOH and Nickel salt solution NiCl2.6H2O (1.188 g, 0.005 mol) were added dropwise with continual stirring and refluxed for four hours monitoring of the course of the reaction with TLC plate. The precipitate was filtered, washed with cold EtOH several times, recrystallized from EtOH, and dried to a constant weight.

Same Procedure is applied for preparation of Manganese complex taking 2:1 mixture of ligand SAP (2.390 g, 0.01 mol) and Mn salt solution MnCl2.4H2O (0.989 g, 0.005 mol).

The formation of the complexes may be represented by the following equation:- 2 LH + NiCl2.6H2O [ NiL2(H2O)2 ] + 2 HCl + 4H2O

2 LH + MnCl2.4H2O [ MnL2(H2O)2 ].2H2O + 2 HCl + 4H2O

5. Result and Discussion :-• The ligand SAP was synthesized by condensation of salicylaldehyde with p-

aminoacetophenone.• Complexes were identified by IR and thermogravimetric analyses of ligand and

complexes. • The ligand prepared is shining yellow; it is soluble in common organic solvents

but insoluble in water. • The manganese (II) and nickel (II) Schiff base complexes prepared are crystalline

orange red and dark red respectively and have decomposition temperatures 214°C and 221°C,respectively. These high decomposition temperatures, revealed the stability of the complex compounds.

• The solubility tests carried out on the ligand and its nickel (II) & manganese (II) complex revealed that they are soluble in most common organic solvents but insoluble in water.

S.No

Compound Formula (F.W. g/mol )

Colour m.p.(0C)

Yield (%)

Elemental Analysis (Calculated) %

C H N M

1. SAP C15H13NO2

(239.273)Shiney yellow

201 71.40 75.29 5.85 5.85 --

2. Ni[(SAP)2(H2O)2] C30H28 Ni N2O6

(571.226)Dark red

221 68.60 63.08 4.94 4.90 10.27

3. Mn[(SAP)2(H2O)2].2H2O C30H32 MnN2O8

(603.469)Orange red

214 66.50 59.71 5.34 4.64 9.11

IR Spectra :-

The ligand contains two potential donorsites: • The phenolic oxygen, • The azomethine nitrogen, In the spectrum of the ligand there is a strong band at 1621 cm-1 due to the C=N

(azomethine) mode. This band shifts to lower energy by 6–11 cm-1 in the complexes, indicating coordination through to azomethine nitrogen.

The ligand exhibits a band at 3250 cm-1 due to O–H (phenolic). The absence of this band in the complexes indicates the deprotonation of the phenolic groups and coordination of the oxygen atoms to metal ion.

In the free ligand, a band at 1260 cm-1 due to C–O (phenolic) shifts to higher frequency by 30– 46 cm-1 in the complexes, indicating the coordination of the phenolic oxygen atom to the metal ion.

The bands in the regions 511-556cm-1 and 450-485cm-1 are attributed to v(M-O) and v(M-N) stretching vibrations respectively, confirming the coordination of the Schiff base to the respective metal ions.

The broad band in the region 3350-3560cm-1 is accorded to v(O—H) stretching vibrations, a feature indicating the presence of water

Assignments Ligand (cm-1) Ni(II)(cm-1) Mn(II)(cm-1)

Aromatic ring

C=C (skeletal)

C-H (in plane)

C-H (stretch)

1460

1178

3035

1463

1171

3048

1461

1166

3045

O-H(phenolic stretch)

(phenolic deform)

3250

1371

--

--

--

--

C-O 1260 1297 1284

C=N (azomethine) 1621 1612 1609

M-N

M-O--

485

538

476

532

O-H (H2O) (stretching) -- 3360 3356

CH

O

N C

O

M

HC

O

NC

O

OH2H2O

CH

O

N C

O

M

HC

O

NC

O

OH2H2O

.2H2O

M = Mn(II)M = Mn(II)

M = Ni(II)M = Ni(II)

From the analyses of the complexes the general molecular structure has been proposed below

Thermal Studies :-

The thermogravimetric (TG) curves for the complexes were obtained at a heating rate of 10°C/min over a temperature range of 50–600°C. Approximately 100 mg samples of the complexes were used in each case.

Thermogravimetric studies of all the complexes showed weight loss up to 145°C, indicating presence of water in the complexes. The inflection of the TG curves of all the complexes at a temperature under 600°C indicates the decomposition of the fully organic part of the chelate, leaving metallic oxide at the final temperature.

S.

No.

Temperatur

e

Compounds

SAP Ni[(SAP)2(H2O)2] Mn[(SAP)2(H2O)2].2H2

O

Weight

loss (%)

Residu

e (%)

Weight

loss

(%)

Residue

(%)

Weight

loss (%)

Residue

(%)

1. 50 0.0 100.0 0.0 100.0 0.0 100.0

2. 100 2.0 98 3.84 96.16 4.32 95.68

3. 300 24.85 75.15 20.56 79.44 21.40 78.60

4. 400 46.88 53.12 20.56 79.44 22.32 77.58

5. 500 47.11 52.89 43.78 56.22 45.10 54.90

6. 600 99.44 0.56 84.24 15.76 86.44 13.56

Significance

Chemistry of metal complexes has progressed enormously perhaps because of their possible applications in the emerging areas like biotechnology, nanotechnology and nanobiotechnology besides having intellectual challenges involved in their structural arrangements.It has been found that coordination compounds exhibited a larger number of applications in past three decades. In recent years, these are being used in the field of medicine, molecular biology, industry and agriculture. However, the most important application of these in the area of catalysis, electrochemistry, dyes, pigments, photography, extractive metallurgy, geochemistry, nuclear fuel cycle, analytical chemistry and biomedical therapy.

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