1

CHAPTER -1

INTRODUCTION

1.1 SCHIFF BASES

Schiff bases are formed typically by the condensation of a primary amine and an

aldehyde/ketone. The resultant compound, R1R2C=NR3 is called a Schiff base, where R1 is an

aryl group, R2 is a hydrogen atom and R3 is either an alkyl or aryl group. However, usually

compounds where R3 is an alkyl or aromatic group are also regarded as Schiff bases. Schiff bases

that contain aryl substituents are substantially more stable and readily synthesised, while those

which contain alkyl substituents are relatively unstable. Schiff bases of aliphatic aldehydes are

relatively unstable and readily polymerisable [1], while those of aromatic aldehydes having

effective conjugation are more stable. In general, aldehydes react faster than ketones in

condensation reactions, leading to the formation of Schiff bases as the reaction centre of

aldehydes are sterically less hindered than that of ketone. Furthermore, the extra carbon of

ketone donates electron density to the azomethine carbon and thus makes the ketone less

electrophilic compared to aldehydes [2].

Schiff bases are generally bidentate (1), tridentate (2), tetradentate (3) or polydentate (4)

ligands capable of forming very stable complexes with transition metals. They can only act as

coordinating ligands if they bear a functional group, usually the hydroxyl, sufficiently near the

site of condensation in such a way that a five or six membered ring can be formed when reacting

with a metal ion.

2

Fig. 1 Some classes of Schiff base ligands

Schiff bases derived from aromatic amines and aromatic aldehydes have a wide variety of

applications in many fields, eg., biological, inorganic and analytical chemistry [3, 4].

Applications of many new analytical devices require the presence of organic reagents as essential

compounds of the measuring system.

Transition metal complexes with Schiff bases have expanded enormously and embraced

wide and diversified subjects comprising vast areas of organometallic compounds and various

aspects of biocoordination chemistry [5]. The design and synthesis of symmetrical Schiff bases

derived from the 1:2 step wise condensation of carbonyl compounds, with alkyl or aryl diamines

and a wide range of aldehyde or ketone functionalities, as well as their metal(II) complexes have

3

been of interest due to their preparative accessibility, structural variability and tunable electronic

properties allowing to carry out systematic reactivity studies based ancillary ligand

modifications. In recent years much effort has been put in synthesis and characterization of

mono- and bi-nuclear transition metal complexes [6].

Schiff bases are used in optical and electrochemical sensors, as well as in various

chromatographic methods to enable detection of enhanced selectivity and sensitivity [7-9].

Among the organic reagents actually used, Schiff bases possess excellent characteristics,

structural similarities with natural biological substances, relatively simple preparation procedures

and the synthetic flexibility that enables design of suitable structural properties [10]. Schiff bases

are widely applicable in analytical determination, using reactions of condensation of primary

amines and carbonyl compounds in which the azomethine bond is formed (determination of

compounds with an amino or carbonyl group) using complex forming reactions (determination of

amines, carbonyl compounds and metal ions) or utilizing the variation in their spectroscopic

characteristics following changes in pH and solvent [11]. Schiff bases play important roles in

coordination chemistry as they easily form stable complexes with most transition metal ions [12].

In organic synthesis, Schiff base reactions are useful in making carbon-nitrogen bonds.

1.2 BIOLOGICAL IMPORTANCE OF SCHIFF BASES

Many biologically important Schiff bases have been reported in the literature possessing

antimicrobial, antibacterial, antifungal, anti-inflammatory, anticonvulsant, antitumour and anti

HIV activities [13-16]. Another important role of Schiff base structure is in transamination [17].

Transamination reactions are catalysed by a class of enzymes called transaminases.

Transaminases are found in mitochondria and cytosal of eukaryotic cells. Schiff base formation

4

is also involved in the chemistry of vision, where the reaction occurs between the aldehyde

function of 11-cis-retinal and amino group of the protein (opsin) [18]. The biosynthesis of

porphyrin, for which glycine is a precursor, is another important pathway, which involves the

intermediate formation of Schiff base between keto group of one molecule of δ-aminolevulinic

acid and ε-amino group of lysine residue of an enzyme.

Schiff base ligands may contain a variety of substituents with different electron-donating

or electron-withdrawing groups and therefore may have interesting chemical properties. They

have attracted particular interest due to their biological activities [19] eg., acting as radio

pharmaceuticals for cancer targeting [20]. They have also been used as model systems for

biological macromolecules. Besides the biological activity, solid-state thermochromism and

photochromism are an another characteristic of these compounds leading to their application in

various areas of materials science such as the control and measurement of radiation intensity,

display systems and optical memory devices [21].

Schiff bases derived from the salicylaldehydes with two or more donor atoms are well

known as polydentate ligands, coordinating in deprotonated or neutral forms. The ability of

metal ions to control the oxidation potentials of organic molecules by complexation has a

significant role in biological electron transfer processes, molecular electronics and also in

catalysis [22]. Schiff bases are used as corrosion inhibitor e.g. fluorinated Schiff base derived

from 3,4-difluorobenzaldehyde and 4,4′-benzidine were used as inhibitor in steel.

1.3 SCHIFF BASE METAL COMPLEXES

Transition metals are known to form Schiff base complexes and Schiff bases have often

been used as chelating ligands in the field of coordination chemistry. Their metal complexes

5

have been of great interest for many years. It is well known that N, O and S atoms play a key

role in the coordination of metals at the active sites of numerous metallobiomolecules [23].

Schiff base metal complexes have been widely studied because they have industrial, antifungal,

antibacterial, anticancer, antiviral and herbicidal applications [24-26]. They serve as models for

biologically important species and find applications in biomimetic catalytic reactions. It is

known that the existence of metal ions bonded to biologically active compounds may enhance

their activities.

There are certain metallo-elements without which the normal functioning of living

organism is inconceivable. Among these metallo-elements so called, ‘metals of life’, four

members form an island. These are Na, Mg, K and Ca, the transition elements are V, Cr, Mn, Fe,

Co, Ni, Cu and Zn. These elements are present at trace and ultra trace quantities and play vital

roles at the molecular level in a living system. These transition elements are known to form

Schiff base complexes.

Schiff base metal complexes have been known since the mid nineteenth century [27] and

even before the general preparation of the Schiff base ligands themselves. Schiff base metal

complexes have occupied a central place in the development of coordination chemistry after the

work of Jorgensen and Werner [28]. Ettlings isolated a dark green crystalline product from the

reaction of cupric acetate, salicylaldehyde and aqueous ammonia. Schiff prepared complexes of

metal-salicylaldehyde with primary amines [29]. Subsequently, Schiff [30] prepared complexes

from the condensates of urea and salicylaldehyde. Delephine prepared complexes [31] by

reacting metal acetate, salicylaldehyde and a primary amine in alcohol and demonstrated a 2:1

stoichiometry.

6

However, there was no comprehensive, systematic study until the preparative work of

Pfeiffer and associates [32]. Pfeiffer and his coworkers [33] reported a series of complexes

derived from Schiff bases of salicylaldehyde and its substituted analogues.

The study of binuclear and polynuclear complexes of transition metal ions has received a

growing attention in recent years. It has been an interesting area for chemists, physicists and

biologists, since these complexes form the basis of several research fields such as bioinorganic

chemistry, magneto chemistry, material science, catalysis, super conductivity and multi electron

redox chemistry etc., [34, 35].

The transition metal complexes having oxygen and nitrogen donor Schiff bases possess

unusual configurations and structural labiality and are sensitive to the molecular environment.

2-hydroxy Schiff base ligands and their complexes derived from the reaction of derivatives of

salicylaldehyde with amines have been extensively studied in great details for their various

crystallographic, structural and magnetic features [36-38].

Particularly, a large number of transition metal complexes of Schiff base ligands derived

from the condensation of salicylaldehyde and 2-hydroxyl-1-naphthaldehyde with various

primary amines became the topic of contemporary research [39, 40]. These Schiff base ligands

may act as bidentate N,O-, tridentate N,O,O-, N,O,N-, N,O,S-, tetradentate N,N,O,O-, hexa

dentate N,N,O,O,S,S- donor ligands [41] etc., which can be designed to yield mononuclear or

binuclear complexes or one-dimensional (1D), two-dimensional (2D) and three-dimensional

(3D) metal-organic frame works [42].

Although several kinds of metal ions are found, metallo proteins with transition metal

ions are numerous. The main reason for the preference of transition metal ions over the other

7

metal ions is ultimately due to their unique features such as the flexibility to adopt more than

one-coordination geometries and the ability to exist in multiple oxidation states. Natural systems

utilize one or both of these features for their feasible biological transformations.

A rational control of the nuclearity of transition metal complexes is important to design

systems with the desired properties as some of these applications require the presence of more

than one metal centre in the particular complex. Indeed, binuclear complexes may have different

reactivity than mononuclear counterparts, thereby enabling transformations inaccessible to single

metal ions [43]. For instance, nucleic acid hydrolysis is postulated to be facilitated by the

cooperative action of two metal ions [44].

Schiff base ligands that are able to form binuclear transition metal complexes are useful

to study the relation between structures and magnetic exchange interactions [45], and to mimic

bimetallic biosites in various proteins and enzymes [46]. The complexes thus play an important

role in developing the coordination chemistry related to catalysis, enzymatic reactions,

magnetism and bioinorganic modeling studies [47]. In this regard, there is much interest in

designing dinucleating ligands and their transition metal complexes.

Metal ions play an important role in living system both in growth and in metabolism. The

active sites of the biomolecules [48] are coordination complexes comprising of one or more

metal ions. The potential relation and those of synthetic coordination complexes has contributed

significantly to the emergence of interdisciplinary field of bioinorganic chemistry. The

bioinorganic chemistry [49] forms the molecular basis of all possible interactions between the

biological molecules and metal ions which is inturn applied in the field of medicine, biology,

8

environmental sciences, catalysis and technology. So the research activities have been grouped

as follows.

1. Study of the metal coordination environment in metallo proteins, nucleic acids,

carbohydrates, membranes [50, 51].

2. Study of the mechanism of reactions occurring at a metal center in enzyme [52].

3. Study of synthetic analog for the active sites in metallo proteins (design, synthesis, structure,

spectroscopy and applications like catalytic reactions and metal sequestering from waste

water and deposits) [53].

4. Design and study of metal containing drugs to cure or prevent diseases (36 g) (synthesis and

mechanism of action)

5. Removal of metal ions and metal compounds from the living system (detoxification) [54]. In

all these fields, both the metal and the ligands are of important for the structure, the stability

and the process that are regulated and catalysed by the metal species.

Of all the Schiff base complexes, those derived from salicylaldimine have been

thoroughly studied so far. A variety of physicochemical investigations on these complexes

provide a clear understanding of their stereochemical and electronic properties. The advantage of

the salicylaldimine ligand system is the considerable flexibility of the synthetic procedure, which

has resulted in the preparation of a wide variety of complexes with a given metal whose

properties are often dependent on the ligand structure.

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1.4 COPPER

Copper is the third most abundant element among the transition metal ions found to be

involved in biological processes [55]. Copper is a bio-essential element with truly unique

chemical characteristics in its two relevant oxidation states I and II [56]. According to its

position as the highest homologue of group XII in the periodic table, copper is a very special

element. The metal-ligand interation in Cu(II) complexes is frequently ionic and favours the

stabilization of the Cu(II) state through the pronounced Jahn-Teller distortion. Different extent of

axial elongation of the octahedron can produce square-pyramidal, square bipyramidal or square

planar geometries.

Copper being an essential trace element, is present in parts per million concentration

range in biological systems. The element functions as a key cofactor in a diverse array of

biological oxidation reduction reactions [57]. Copper containing proteins (hemocyanin,

tyrosinase, catecol oxidase etc.,) are involved in various processes in living systems [58, 59].

1.5 NICKEL

The Ni(II) ions play a central role in biological redox metalloenzymes like plastocyanin,

hemocyanin, azurin, galactose oxidase and others [60]. Nickel compounds are present in the

active sites of urease and are used extensively in the design and construction of new magnetic

materials.

1.6 VANADIUM

Vanadium is an abundant bio-element in diverse biological system [61]. It has many well

defined functions such as halogenations of organic substrates, activation or fixation of nitrogen

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through an alternation pathway [62] or as a phosphate analogue in enzymes reactions [63]. Some

vanadium compounds have pharmacological effects, eg., stimulating glucose uptake and

inhibiting lipid break down [64]. Additionally, vanadium is a biocompatible metal ion used

earlier in insulin mimetics and antitumour agents [65]. Vanadium binds to transport proteins and

that the ability allows it to be accumulated by various terrestrial organisms, e.g., fungi, mosses

and lichens. In the marine environment, ascidians accumulate vanadium to high levels in special

blood cells, vanadocytes [66].

Vanadium(IV) is the most stable oxidation state under ordinary conditions and majority

of vanadium(IV) compounds contains the (VO)2+

unit which can persist through a variety of

reactions and in all physical states. The (VO)2+

ion forms stable anionic, cationic and neutral

complexes with several types of ligands and has one coordination position occupied by the

vanadyl oxygen.

1.7 COBALT

A wide variety of Co(II) complexes are known to bind dioxygen more or less reversibly

and are therefore frequently studied as model compounds for natural oxygen carriers and for

their use in O2 storage, as well as in organic synthesis due to their catalytic properties under mild

conditions [67]. In this respect, Co(II) complexes with N, O- donor ligands containing binding

units suitable either for the coordination of a single metal ion or for assembling dimetallic

centers have been shown to be particularly useful. In aprotic solvents, at atmospheric pressure

and room temperature, cobalt chelated complexes with Schiff bases catalyses the oxygenation of

indols, flavones, nitroalkanes, hydrazones, olefins, etc [68]. The cobalt(II) complexes with tetra

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dentate Schiff base ligands which coordinate through N2O2 donor atoms have been extensively

studied as oxygen carriers and also as catalyst for water splitting systems [69].

1.8 EFFECT OF COMPLEXATION ON BIOLOGICAL ACTIVITY

The metallo elements which are present in trace and ultra-trace quantities play vital roles

at the molecular level in a living system. In a healthy body, of an adult, the trace and

ultra-trace elements weigh less than 10 grams in total but life depends upon these elements for

more than this figure [70]. The transition metal ions are responsible for the proper functioning of

different enzymes. If their concentration exceeds a certain level, then their toxic effects are

evident.

It has been found that the activity of the biometals is attained through the formation of

complexes and the thermodynamic and kinetic properties of the complexes govern the mode of

biological action. Sometimes, the permeability, ie., lipophilicity of drugs increased through the

formation of chelates invivo and the drug action is significantly increased due to much more

effective penetration of the drug into the site of action. The knowledge of drug action invivo is

extremely important in designing more potential drugs.

Interaction of various metal ions with antibiotics may enhance or suppress their

antimicrobial activity but usually in many cases the pharmacological activity of antibiotics after

complexation with metals is enhanced as compared to that of the free ligands [71]. Generally it

has been observed that transition metal complexes have greater activity and less toxic effects.

The preparation and study of inorganic compounds containing biologically important

ligands is made easier because certain metal ions are active in many biological processes. The

fact that copper, together with magnesium, calcium, iron, zinc, cobalt, chromium, vanadium and

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manganese are essential metallic elements and exhibit great biological activity when associated

with certain metal-protein complexes, participating in oxygen transport, electronic transfer

reactions or the storage of ions [72], has created enormous interest in the study of these systems

containing these metals [73].

1.9 ANTIMICROBIAL ACTIVITY

An antimicrobial is a substance that kills or inhibits the growth of microorganisms such

as bacteria, fungi, or protozoans as well as destroying viruses. Antimicrobial drugs either kill

microbes (microbicidal) or prevent the growth of microbes (microbistatic).

The history of antimicrobials begins with the observations of Pasteur and Joubert, who

discovered that one type of bacteria could prevent the growth of another. Technically, antibiotics

are only those substances that are produced by one microorganism that kill, or prevent the

growth, of another microorganism. Of course, in today's common usage, the term antibiotic is

used to refer to almost any drug that cures a bacterial infection. Antimicrobials include not just

antibiotics, but synthetically formed compounds. Now, most of these infections can be cured

easily with a short course of antimicrobials.

In the last years, the attention in this field was oriented to inorganic species among the

organic ones. Although many complexes showed a good antimicrobial activity so far only a few

are used as metallo antibiotics (antiseptics and antimicrobial) or disinfectants [74]. So far a good

antimicrobial activity was observed for complexes bearing a biocation [75] and a multidentate

ligand and / or having a proved antimicrobial activity [76].

Among biocations, copper is preferred having in view: (i) the low human toxicity

associated with the both presence of albumin in the plasma and the metalotionein in the cytosal;

(ii) the borderline character and the fact that forms the most stable complexes among the Irving

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William series of cations; (iii) the stereo chemical versatility; (iv) the easiness to change its

oxidation state and; (v) the known biological activity including the ability to inhibit enzyme, one

of the mechanisms responsible by the antimicrobial activity [77].

The synthesis and characterization of new metal complexes with antibacterial and

antifungal agents are of great importance for understanding the drug-metal ion interaction and

for their potential pharmacological use. New kinds of chemotherapeutic agents containing Schiff

bases have gained significant attention among biochemists.

Five different microbial species were used to screen the possible antimicrobial activity of

the synthesised metal complexes. Of the species used, Staphylococcus aureus is one of the most

common gram-positive bacteria causing food poisoning. Its source is not the food itself, but the

humans who contaminate foods after they have been processed. Gram-negative bacteria are

represented by Escherichia coli, which belong to the normal flora of humans. However, an

enterohemmoragic strain of E. coli has caused serious cases of food poisoning and preservatives

to eliminate its growth are needed. A clearly visible spoiling agent of bakery products is the

mold that forms black-centered spots on the surface of products is Aspergillus niger. A typical

opportunist, Candida albicans is the microbe responsible for most clinical yeast infections, e.g.,

in mouth infections.

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1.10 REVIEW OF LITERATURE

Hasty et al., (1977) synthesized copper(II), nickel(II) and cobalt(II) complexes having an

imino benzene moiety bridging between the two metal ions [78]. The ligand (I) was obtained by

the condensation of salicylaldehyde with m- or p-phenylenediamine. The copper and nickel

complexes showed antiferromagnetic interaction and cobalt complex showed weak

antiferromagnetic exchange interactions.

I

Condensation of 2,2′,6,6′-tetraaminobiphenyl with salicylaldehyde gives a binucleating

ligand (II) which was used to prepare Cu2(sal-tabp), Ni2(sal-tabp).H2O and Co2(sal-tabp).½ H2O.

II

Karaböcek et al., (1997) synthesised and characterised mono- and di- nuclear copper(II)

complexes (III) with a tetradentate Schiff base, 4′,5′-bis(salicylideneimino)benzo-15-crown-5

[79]. This ligating system provides an additional active site besides conferring on the copper(II)

15

ion in a square planar N2O2 environment which not only mimics the active site in galactose

oxidase but also has a role in molecular magnetism.

III

Kanadaswamy et al., (1998) synthesised and studied remote donor set of complexes (IV)

derived from methylene bridged bis (tridentate) ligands with the aim to study the influence of

remote donor set of ligands on complex properties [80]. The EPR spectra is similar to

mononuclear Cu(II) complex with nuclear spin 3/2. Variable temperature magnetic susceptibility

measurements show no exchange interation between Cu (II) centers.

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IV

Sureshan et al., (1998) prepared Mn(II) complexes (V) of Schiff base obtained by the

condensation of pyridine-2-carboxaldehyde and longer aromatic diamines like

4,4′-diaminodiphenyl, 4,4’-diaminodiphenylmethane and 4,4′-diaminodiphenylether respectively

[81]. The complexes have been characterised by elemental analysis, spectral, magnetic,

electrochemical and FAB mass spectral studies. The complexes have been used as catalyst for

the epoxidation of olefin using iodosyl benzene as oxidant.

V

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Tümer et al., (1999) prepared, characterised and studied the antibacterial activity of

binuclear Cu(II), Co(II), Ni(II), VO(II) and Zn(II) complexes (VI) derived from

3-hydroxysalicylaldehyde, 4-hydroxysalicylaldehyde and 5-bromosalicylaldehyde with

N-(pyridyl)-2-hydroxy-3-methoxy-aminobenzylamine [82]. Antimicrobial activities of the

ligands and their complexes have been tested against the strains of Bacillus subtilis, Micrococcus

luteus, Saccharamyes cerevisiae and Candida albicans. Thermal properties of the complexes

have been studied by thermogravimetric and differential analysis techniques which showed the

presence of hydrated or coordinated water molecules.

VI

Rajavel et al., (1999) synthesised and characterised binuclear Schiff base metal

complexes derived from 2-aminobenzaldehyde (VII) [83]. The synthesised complexes were

characterised by physicochemical methods. Low temperature magnetic moment shows the

presence of weak antiferromagnetic interactions between the metal ions in benzidine type

complexes.

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VII

Kasumov (2001) synthesised bis-[N-(2,6-di-t-butyl-1-hydroxylphenyl)

salicylideneminato]copper(II) complexes bearing OH and CH3O substituents on the

salicylaldehyde moiety (VIII) [84]. Their spectroscopic properties as well as redox reactivity

towards PbO2 and PPh3 were examined by EPR and UV spectroscopy.

VIII

Nathan et al., (2003) have synthesised N,N’-polymethylene-bis(salicylaldiminato)

copper(II) complexes with alkyl back bones ranging from two to eight carbons (IX) [85]. The

complexes are monomeric when the alkyl chain length is relatively short (two, three and four

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CH2 groups) but are dimers when the chain length becomes longer (five, six and eight CH2

groups).

IX

Tuna et al., (2003) have reported synthesis of ligand (X) derived from 3-formyl-salicylic

acid to form the complex 3-[N-2-(pyridylethyl)formimodoyl]salicylic acid [86]. The synthesised

ligand and its metal complexes were characterised by elemental analysis, molar conductance,

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

magnetic studies.

X

Srinivasan et al., (2004) synthesised a dicopper complex (XI) of a Schiff base,

2-[(4-methyl-pyridin-2ylimino)-methyl]-phenol with a bridging acetato ligand characterised by

single crystal XRD, EPR, magnetic susceptibility, IR, UV-Vis, CV and elemental analysis. One

of the copper atoms in the binuclear complex adopts a square-pyramidal geometry, while the

other copper assumes a square planar geometry [87]. EPR spectrum in frozen solution confirms

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the interaction between the two copper ions. The molar conductance for the complex indicates

that the complex is a 1:1 electrolyte.

XI

Shu-Fei Huang et al., (2004) synthesised, characterised and studied the magnetic

properties of µ-alkoxo-µ-pyrazolato bridged dicopper(II) complexes (XII) [88]. The

variable-temperature magnetic susceptibitity measurements revealed that the metal centers in

both the compounds are anti ferromagnetically coupled with J = -200 cm-1

and J = -175 cm-1

for

the complexes. The magnetic behaviours have been explained on the basis of two opposing

factors, complementarity and counter complimentarity of magnetic orbitals.

[Cu2II(L

1-F)(µ-prz)] and [Cu2

II(L

1-2OMe)(µ-prz)]0.5CH3CN (prz = pyrazolato;

H2L1- F = 1,3-bis-(3-fluorosalicylideneamino)-2-propanol;

H2L1-2OMe = 1,3-bis-(4,6-dimethoxysalicylideneamino)-2-proponal.

21

XII

Ghames (2006) prepared, the structural and electrochemical studies of Co(II), Ni(II),

Cu(II) and Cd(II) complexes with a new symmetrical N2O2 Schiff base and crystal structure of

the ligand 1,2-di[4-(2-imino-4-oxopentane)phenyl]ethane was also studied [89]. The

coordination occurs through the N2O2 system.

XIII

The binuclear nickel(II) complex (XIII) in which each Ni(II) ion presents a square planar

arrangement and the Schiff base acts as a symmetrical tetradentate ligand through the

keto- amino tautomer.

Sallam (2006) prepared binuclear copper, nickel and cobalt complexes (XIV) of the

Schiff bases obtained by the condensation of glycylglycine with acetyl acetone, benzoyl acetone,

dibenzoylmethane and thenoyltrifluoroacetone [90]. The complexes were characterised by

elemental analysis, conductivity measurements, magnetic moments, IR, UV-Visible spectra,

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EPR, X-ray diffraction, TGA, DTA and DSC thermal analysis. All the complexes were

non-electrolytes with low magnetic moments that indicate spin-spin or antiferro magnetic

exchange interactions. Spectral properties support square planar and square pyramidal or trigonal

bipyramidal structure provided by the N2O2 chromophores. A mechanism for thermal

decomposition is proposed for complexes.

XIV

Wei-Hua Wang et al., (2006) synthesised binuclear neutral nickel complexes (XV)

bearing bis (bidentate) salicylaldiminato ligands [91]. The structure was confirmed by X-ray

crystallography. Catalytic activities for ethylene polymerization, molecular weights and

molecular weight distribution of polyethylene have been investigated under various reaction

conditions.

XV

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Tümer et al., (2007) synthesised and characterised divalent metal [Cd(II), Cu(II), Co(II),

Ni(II), Zn(II)] complexes (XVI) [92]. Their electrochemical, catalytic, thermal and antimicrobial

studies have also been carried out. Electrochemical properties of the complexes Cu(II) and Ni(II)

were investigated. The antimicrobial property of the synthesised complexes was evaluated using

antibiotic ampicillin, streptomycin as standard antibacterial agent. The antibiotic nystatin is the

standard antifungal.

XVI

Mehmet Sönmez (2008) synthesised binuclear Cu(II) complexes of ONO tridentate

heterocyclic Schiff base (XVII) derived from 1-amino-5-benzoyl-4-phenyl-1Hpyrimidine-2-one

with substituted salicylaldehyde and 2-hydroxynaphthaldehyde [93].

XVII

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Jammi et al., (2008) synthesised chiral binuclear copper(II) complexes (XVIII) from

aldehydes and amino alcohols [94]. Their catalysis was studied for the addition of nitroalkanes to

aldehydes at ambient conditions. The copper(II) atoms are tetra coordinated with distorted square

planar geometry.

R = t - Bu, H, R′ = Me, i – Pr, t – Bu, S – Bu

XVIII

Aslantas et al., (2008) prepared and characterised the dimeric complex, [C20H20CuN2O2]2

(XIX) by thermal analysis, IR and single-crystal X-ray diffraction techniques [95]. The Cu atom

in the binuclear complex exists in a distorted square-pyramidal configuration, defined by three O

atoms and two N atoms. The crystal structure is stabilized by intermolecular C-H-----O hydrogen

bonding interaction. Cyclic voltammogram of the complex exhibits quasi-reversible one electron

transfer processes.

XIX

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Maxim et al., (2008) synthesised copper(II) and zinc(II) complexes using the ligands

(XX) N-[(2-pyridyl)-methyl]-salicylimine (Hsalampy), N-[2-N,N-dimethyl-amino)-ethyl]-

salicylimine (Hsaldmen) and N-[(2-pyridyl)-methyl]-3-methoxy-salicylimine (Hvalampy) [96].

XX

The first two ligands were obtained by reacting salicylaldehyde with

2-aminomethylpyridine and N,N′-dimethylenethylenediamine, respectively, while the third one

results from the condensation of 3-methoxysalicylaldehyde with 2-aminomethylpyridine. The

magnetic and luminescence properties of the complexes at room temperature have been

investigated.

Esin İspir (2009) have reported the synthesis of Schiff base ligand (XXI) derived

from the reaction of p-aminoazobenzene with salicylaldehyde, 2,4-dihydroxybenzaldehyde and

2,3,4-trihydroxybenzaldehyde respectively [97]. The oxidative C-C coupling properties of the

Co(II) and Cu(II) complexes were investigated on the sterically hindered 2,6-di-tert-butylphenol

(DTBP). The Schiff base ligands and their complexes were evaluated for both their invitro

antibacterial activity using the disc diffusion method.

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XXI

Welby et al., (2009) synthesised and studied the crystal structures of mono-, di- and

trinuclear cobalt complexes of a salen type ligand (XXII), N,N′-bis(salicylidene)-meso-1,2-

diphenyl ethylenediamine [98].

(mdp sal H2)

XXII

Ahmed et al., (2009) prepared and characterised binuclear dichloro-bridged copper(II)

complexes, the ligands (XXIII) have been synthesised by the condensation of acetyl acetone and

p-phenylenediamine [99]. Each copper showed square planar geometry with ONClCl

coordination, a mixed valence Cu(I) Cu(II) complex has been suggested. The low magnetic

moment values of binuclear copper complexes are attributed to the anti-ferromagnetic moment

interaction between two central metal ions

XXIII

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Stringer et al., (2009) synthesised and characterised binuclear palladium(II) complexes

(XXIV) of salicylaldimine dithiosemicarbazones obtained by the reaction of various ethylene

and phenylene-bridged dithiosemicarbazones with Pd(PPh3)Cl2 [100]. The salicylaldimine

thiosemicarbazone ligands coordinate to palladium in a bidentate manner, through the phenolic

oxygen, imine nitrogen and thiolate sulphur atoms.

XXIV

Square planar geometry was observed for the complexes. Preliminary antitumour activity

of the dithiosemicarbazone ligands showed a moderate to good cytotoxicity for the indicated cell

lines. Biological activity of the palladium(II) complexes of dithiosemicarbazones have not been

determined due to its poor solubility.

Leelavathy et al., (2009) synthesised and characterised unsymmetrical macrocyclic

binuclear vanadyl complexes (XXV) [101]. The electrochemical, antimicrobial, DNA binding

and cleavage studies have also been carried out. The cyclic voltammetric studies showed that the

complexes containing aromatic diimines get reduced at higher negative potentials than the

complexes containing aliphatic diimines. All the complexes showed noticeable growth inhibition

of some plant pathogenic fungal species and human pathogenic bacterial species.

28

XXV

Abdalrazaq et al., (2010) synthesised and characterised dinuclear complexes of the type

[M2LnCl2(H2O)2], where n = 1 or 2, M = Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) [102]. The

tetradentate dianion Schiff base ligand (XXVI) was prepared by the condensation of hydrazine

with acetyl acetone or acetyl acetanilide.

XXVI

Rosu et al., (2010) synthesised complex (XXVII) combinations of Cu(II), V(IV) and

Ni(II) with Schiff bases obtained through the condensation of 4-amino-1,5-dimethyl-2-phenyl-

29

1H-3-pyrazol-3(2H)-one(antipyrine) with 2-hydroxylbenzaldehyde, 4-hydroxy-5-

methoxyisophthalaldehyde and 4,5-dihydroxyisophthalaldehyde respectively [103]. The

characterization of the complexes was done by 1H NMR,

13C NMR, UV-Visible, IR, EPR

spectroscopic and molar conductance studies. The effect of these complexes on proliferation of

human leukemia cells and their antibacterial activity against Staphylococcus aureus, Escherichia

coli and Candida albicans were studied. Tetracycline and fluconazole were used as the control

drugs in the case of bacteria and fungi.

XXVII

In the copper(II) complex, the geometric parameter G = 3.68 confirms the existence of

some exchange interactions between the Cu(II) centres.

Sibous et al., (2010) synthesised, characterised and studied the

electrochemical behavior of Co(II), Ni(II) and Cd(II) complexes (XXVIII) with N2O2 donor

ligands derived from 4,4’-diaminobiphenyl and 2-hydroxybenzaldehyde or 2,4-

dihydroxybenzaldehyde [104]. The coordination of the metal ions is through nitrogen and

oxygen atoms. The cobalt(II) and cadmium(II) compounds present a distorted tetrahedral

geometry while nickel(II) complexes exhibit a typical square planar structure.

30

XXVIII

31

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