Chapter I

Introduction

Coordination chemistry is gaining great attention in recent years

particularly in the designing of respiratory, slow release, long acting drugs in

nutrition and in the study of metabolism [1]. One of the most important

features of metal coordinated systems is concerted spacial arrangement of

ligands around metal ion. Coordination compounds exhibit different

characteristic properties which depend on metal ion to which the ligands are

bound, the nature of the metals as well as the type of ligand. Earlier workers

reported that some drugs show increased activity when administered as metal

chelates rather than as organic compounds [2]. The metal complexes have

found application in various fields of human interest. Schiff bases, named

after Hugo Schiff (1834-1915) and their transition metal complexes continue

to be of interest even after hundred years of study. Schiff bases are regarded

as “privileged ligands” due to their ability to form complexes with a wide

range of transition metal ions yielding stable and strongly coloured metal

complexes. They are considered to be among the most important

stereochemical models in transition metal coordination chemistry due to their

preparative accessibility and structural diversity [3].

Among the organic compounds, Schiff bases possess excellent

properties such as, structural similarities with natural biological substances,

simple procedures of preparation, flexibility in synthesis, wide range of

applications and diverse structural modifications [4, 5]. Schiff bases have

been reported to show a variety of biological actions by virtue of azomethine

linkage which is responsible for various antibacterial, antifungal, herbicidal,

2 Chapter 1

clinical and analytical activities [6]. An interesting application of Schiff

bases is their use as an effective corrosion inhibitor, which is based on their

ability to spontaneously form a monolayer on the surface to be protected [7].

A large number of different Schiff base ligands have been used as cation

carriers in potentiometric sensors as they have shown excellent selectivity,

sensitivity and stability for specific metal ions [8, 9]. Schiff bases have wide

applications in food industry, analytical chemistry and agriculture [10, 11].

Schiff bases can be used in analytical chemistry as chromogenic agents for

the determination of metal ions in food samples. The importance of

determination of heavy metal ions, such as nickel, in environment samples is

undoubtedly a serious potential hazard to the human beings and other

organisms. Some natural food samples are analysed for the presence of

nickel by some novel tetradentate Schiff bases which are used as

chromogenic agents [12]. New kinds of chemotherapeutic agents containing

Schiff bases have gained significant attention among biochemists and some

of them are commonly administered intervenously to detect liver diseases in

clinical treatment [13]. The use of appropriate multidentate chelating ligands

removes the undesirable effects of metal ions and can deactivate either the

carcinogenic metal or enzyme which is essential for the rapid growth of both

healthy and malignant cells. Schiff bases derived from aromatic amines and

aromatic aldehydes are used in optical and electrochemical sensors as well as

in various chromatographic methods to enable detection of enhanced

selectivity and sensitivity [14]. Schiff bases belong to a widely used group of

organic intermediates important for the production of speciality chemicals

like pharmaceuticals and rubber additives [15]. They also have uses as liquid

crystals [16].

Introduction 3

Schiff bases have been used as ligands because of their ability to

create stable coordination compounds with metals having different oxidation

states. Complexes derived from Schiff bases are very useful in providing

synthetic models for the metal containing sites in metalloproteins and

enzymes. Extensive studies have been conducted on complexation of Schiff

bases with metals due to their facile synthesis, easily tunable electronic,

steric and physiochemical properties. Though biosynthetic processes do not

use metals as additional cofactors, it was frequently reported that metal ions

can promote many of these reactions non-enzymatically, the promoting

effect of metal ions is due to stabilization of intermediate Schiff base

formed[17,18].

Some Schiff base metal complexes have excellent light emitting and

charge transforming properties. The application of Schiff base complexes in

full colour flat-panel displays are pointed out by experimental reports [19]. A

considerable number of Schiff base complexes have potential biological

interest, being used as more or less successful models of biological

compounds [20]. Designing of Schiff base molecule capable of binding and

cleaving DNA at specific sites has been an area of interest. Schiff base

complexes that bind to DNA have been used as diagnostic probes for both

structural and functional aspects of nucleic acid in the development of new

therapeutic agents [21, 22]. Considerable attention continues to be given to

Schiff base ligands and their metal complexes since their properties can be

greatly modified through the introduction of different substituents.

1.1 Scope and Objectives of present work

Transition metal complexes having unique electronic and

spectroscopic signatures offer a multitude of coordination geometries and

mechanism of cytotoxic action which is related to DNA binding affinity [23].

4 Chapter 1

The biological activity strongly depends on structure. Besides this, metal

complexes can also utilize or create open coordination sites for DNA

binding. The molecular design aims mainly to obtain device quality

materials, structure- property relationships and guidance in molecular design

for improved molecules. With increasing knowledge of properties of

functional groups as well as nature of donor atoms and central metal ion,

ligands with more selective chelation groups are used for complex formation

studies.

Researches based on new Schiff bases and their metal complexes

represent one of the most attracting areas of material science, catalysis and

chemical research. Although the synthesis and complexation of Schiff bases

have been under study for many years, considerable attention continues to be

given to these and related metal complexes since their properties can be

greatly modified through the introduction of different substituents.

Designing of suitable polydentate Schiff base ligands to combine with a

metal ion along with a pseudohalide anion has opened a new era of synthesizing

metal complexes of particular choice [24]. So with the intention of obtaining

information about the coordination chemistry of the metal complexes, it is

proposed to study the complexes of Fe(III), Co(II), Ni(II) and Cu(II) ions of two

Schiff bases 2,3-dimethyl-4-formyl-[2′-(aminomethyl)pyridine]-1-phenyl-3-

pyrazolin-5-one (DFAPP) and ethylenediaminobi(chromone-3-carbaldehyde)

(FCED). These Schiff bases have been characterised by TLC, elemental

analysis, IR, UV-VIS, 1H as well as 13C NMR spectra. The new complexes

have been characterized by several techniques such as elemental analysis,

molar conductance in non-aqueous solvents, infrared, electronic as well as

EPR spectra, magnetic susceptibility measurements and TG/DTA. Some of

Introduction 5

the complexes have been also characterized by single crystal X-ray

diffraction technique.

1.2 Iron – General Chemistry

Iron is a white lustrous metal with electronic configuration

[Ar]3d64s2. It is not particularly hard but quite reactive. Oxidation states of

+2 and +3 are most characteristic of iron but derivatives, in which oxidation

state is -2, 0, +4 and +6, are also known. The iron(II) and iron(III) states lie

much closer together in stability and this accords the well-known properties of

ferrous and ferric solutions which are readily interconverted by use of mild

oxidizing and reducing agents. The relative stability of these two oxidation

states in acidic aqueous solution is defined by standard electrode potential of

+0.77V for Fe3+/Fe2+ couple. The potential is such that the hydrated Fe2+ is

thermodynamically unstable with respect to atmospheric oxidation. The

chemistry of iron including its importance in biology is closely associated with

the ready interconversion of these two oxidation states and with the

dependence of the redox potential on ligand environment [25].

The high charge density of Fe3+ is also responsible for its strong

affinity for oxygen and fluorine donors [26]. It is for this reason that Fe3+

unlike Fe2+, forms few stable complexes with ligands such as ammonia or

simple amines which are also good Bronsted bases in aqueous solution. Fe3+

has a d5electronic configuration with its high spin (S = 5/2) in most of its

complexes. There is a possibility of stabilization of low spin (S = 1/2)

ground state in strong octahedral fields such as generated by CN- and in

many bi- or polydentate ligands containing unsaturated nitrogen. In addition,

the intermediate spin state (S = 3/2) may be produced in fields of lower

symmetry.

6 Chapter 1

1.2.1 Iron(III)- Coordination Chemistry

Fe(III) forms many complexes with ligands which coordinate

preferentially through oxygen apart from nitrogen. Fe(III) displays various

coordination numbers ranging from 3 to 8 but the most common

coordination number is 6. The various coordination numbers and their

corresponding geometries are listed in Table 1.1.

Table 1.1 Various coordination geometries displayed by iron(III) complexes

Coordination number Geometry Example

3 Trigonal [Fe(N(SiMe)2)3]

4 Tetrahedral [FeCl4]-

5 Square pyramidal [Fe(acac)2Cl]

5 Trigonal bipyramidal [FeCl5]2-

6 Octahedral [Fe(H2O)6]3+

7 Pentagonal bipyramidal

[Fe(EDTA)(H2O)]-

8 Dodecahedral [Fe(1,8naphthylidine)4](ClO4)2

Fe3+ has a d5 electronic configuration. Thus complexes with weak

field ligands will have a high spin arrangement with five unpaired electrons.

The affinity of Fe(III) for amine is low. Complexes with ammonia are

unstable in water. Complexes with chelating N ligands such as dipyridyl are

formed. Dipyridyl ligands cause spin pairing to form fairly stable complexes.

Amines such as EDTA form complexes among which seven coordinate

[Fe(EDTA)(H2O)]- is important.

Introduction 7

The anion complexes of Fe(III) are more stable and easier to obtain

than Fe(II). Iron(III) chloride forms adducts with donors, giving compounds

with tetrahedral geometry such as [FeCl3L] (L = ether, large phosphine). The

tetrahedral [FeCl4]-, trigonal bipyramidal [FeCl5]

2-, octahedral [FeCl6]3- and

face sharing bioctahedral [Fe2Cl9]3- can be obtained with large anions.

The oxygen donor ligands have high affinity for iron(III) and the

complexes are formed by phosphates, oxalates, glycerol and sugars [27].

A characteristic feature of iron(III) is its ability to form oxo and hydroxo

bridges in which there exist antiferromagnetic coupling between the iron

atoms. In µ-oxo dimers such as [{Fe(salen)}2O], the magnetic moment is

reduced to around 2 BM per iron atom because of this antiferromagnetic

coupling. A complex with sulphur bridge is seen in [Fe(salen)2]S.

Several low spin complexes of Fe(III) display spin cross over

phenomena. For instance, a variety of trigonally distorted octahedral

dithiocarbamate complexes [Fe(S2CNR2)3] can be high spin or low spin

depending on temperature.

1.2.2 Iron(III)- Electronic spectra and Magnetism

All d-d transitions of high spin iron(III) are spin forbidden and

Laporte forbidden because of the absence of excited states of same spin

multiplicity due to the orbital singlet nature. The Russel-Saunders term 6S

changes its notation to 6A1 in a cubic field while the first excited state 4G

splits in to two T states (4T1 and 4T2) and in to a degenerate pair 4A1 and 4E.

Since there is no excited state with same spin multiplicity all electronic

transitions are Laporte forbidden and spin forbidden. Consequently all

electronic transitions have an extremely low molar extinction coefficient

8 Chapter 1

value. In fact it is difficult to locate those doubly forbidden transitions. The

ligand field transitions for the high spin d5 ions are

6A1 → 4T1(G)

6A1 → 4T2(G)

6A1 → 4A1(G) , 4E(G)

6A1 → 4T2(D)

Because of the forbidden nature of the ligand field transitions, many

salts and complexes of iron(III) have little or no colour. The hexaaqua iron

has a very pale violet colour while [FeF6]3- is virtually colourless. But the

intense colour of certain high spin iron(III) compounds may be due to ligand

to metal charge transfer transitions (LMCT).

In high spin complexes magnetic moments are always close to the

spin only value of 5.9 BM because ground state has no orbital angular

momentum and there is no effective mechanism for introducing any coupling

with excited states. The low spin complexes with t2g5 configuration, which

usually have considerable orbital contribution to their moments at about

room temperature, give values of ~2.3 BM. The moments are, however,

intrinsically temperature dependent and at liquid nitrogen temperature they

decrease to ~ 1.9 BM. There is evidence for very high covalence and electron

delocalization in low spin complexes such as [Fe(bipy)3]3+ and [Fe(phen)3]

3+.

1.3 Cobalt(II)- General Chemistry

Cobalt is a hard, ductile, lustrous bluish-grey metal with B.P.

1495°C. It has similar appearance with iron and nickel. Co-59 is the most

stable isotope of cobalt. It is ferromagnetic with a Curie temperature of

1121°C. The reduction potential of Co2+/Co is -0.277 V, but it is relatively

Introduction 9

unreactive. The metal is attacked by atmospheric oxygen and water vapour at

elevated temperatures giving CoO [28]. The most common oxidation states

of cobalt are +2 and +3. A few Co4+ and Co5+ compounds exist [29].

Examples are Cs2[CoF6] and [Co(1-norbornyl)4]+. Co3O4 is obtained by

oxidation of cobalt at 400-500°C in air [30].

Cobalt(II) forms an extensive group of simple and hydrated salts.

The cobalt salts are blue when anhydrous and pink or red when hydrated. In

aqueous solutions having no complexing agents, oxidation of cobalt(II) to

cobalt(III) is difficult. In presence of complexing agents the stability of Co3+

is greatly increased.

1.3.1 Cobalt(II) – Coordination Chemistry

Mainly octahedral or tetrahedral complexes are formed by cobalt(II)

but five coordinate and square planar species are also known. It shows

coordination numbers ranging from 3 to 8. Some examples are listed in table

1.2.

Table 1.2 Various coordination geometries displayed by cobalt(II) complexes

Coordination number Geometry Example

3 Trigonal [Co2(NPh2)4]

4 Tetrahedral [Co(NH3)4]2+

4 Square planar [(Ph3P)2N]2[Co(CN)4]

5 Trigonal bipyramid [Co(NP3)Br]+

5 Square pyramid [Co(CN)5]3-

6 Octahedral [Co(H2O)4Cl2]

8 Dodecahedral Ph4(As)2[Co(NH3)6]2+

10 Chapter 1

There are more tetrahedral complexes of Co(II) than those of other

transition metal ions. This is in accordence with the fact that for d7 ion,

ligand field stabilization energies disfavor the tetrahedral configuration

relative to octahedral one to a smaller extent than for any other dn

configuration (1 ≤ n ≤ 9). Because of the small stability difference between

octahedral and tetrahedral Co(II) complexes, there are several cases in which

the two types with the same ligand may be in equilibrium [31]. An example

is that of thiocyanates in methanol.

Tetrahedral complexes are generally formed with monodentate

anionic ligands such as Cl-, Br-, I-, SCN-, N3- and OH-. But tetrahedral

complexes of the type CoL2X2 are also formed (where L = neutral ligand and

X = anionic ligand). With the less hindered ligands of this type, association

to give a higher coordination number often occurs. Co(II) forms planar

complexes with several bidentate monoanionic ligands like

dimethylglyoximate. Several neutral bidentate ligands also give planar

complexes although it is either known or reasonable to presume that the

accompanying anions are coordinated to same degree, so that these

complexes could also be considered as much distorted octahedral ones. With

tetradentate ligands such as porphyrins, planar complexes are also obtained.

Five coordinate species can form trigonal bipyramidal or square pyramid

complexes and in some limiting cases it may have an intermediate

arrangement.

1.3.2 Cobalt(II) - Electronic Spectra and Magnetism

Cobalt(II) occurs in a great variety of structural environments

because of the electronic structures and hence the spectral and magnetic

properties of the ion are extremely varied. Tetrahedral complexes have more

Introduction 11

intense colour than octahedral complexes. This is because tetrahedron lacks a

centre of symmetry and thus overcomes the Laporte selection rule, whereas

octahedral complexes have to rely on asymmetric vibration of ligands to

destroy the center of symmetry. In each case the visible spectrum is

dominated by highest energy transitions 4T1g(F) → 4T1g(P) for octahedral and 4A2 → 4T1(P) for tetrahedral geometries. A simplified Orgel diagram for

octahedral and tetrahedral cobalt(II) is shown in Figure 1.1.

Fig. 1.1 Orgel diagram for tetrahedral and octahedral cobalt(II)

In both cases there is a quartet ground state and three spin- allowed

electronic transitions to excited quartet states. In octahedral systems the 4A2g

level is usually close to 4T1g(P) level and transitions to these two levels are

close together. Since the 4A2g state is derived from a ���� ��

� configuration,

and 4T1g(F) ground state is derived mainly from ���� ��

� configuration, the

4T1g(F) → 4A2g transition is essentially a two electron process. For octahedral

complexes there is one more spin allowed transition 4T1g(F) → 4T2g which

generally occurs in near-IR region.

12 Chapter 1

For tetrahedral complexes 4A2 → 4T1(F) and 4A2 → 4T1(P) transitions

appear as multiple absorption in the near- IR and visible regions respectively.

The intensities of these bands are generally in the order of 10-102 for the

former and 102 - 2 x 103 mol-1 cm-1 for the latter and allow fairly clear cut

distinction to be made between tetrahedral and octahedral cobalt(II)

derivatives. The third transition, 4A2 → 4T2 is orbitally forbidden for regular

tetrahedral Co(II) complexes although vibronically allowed. No low spin

complex of Co(II) in tetrahedral coordination has been found [32].

Low spin octahedral cobalt(II) complexes are rare since the 10 Dq

greater than 15,000 cm-1 is needed and is indeed high for doubly ionized ion

of 3d series. Only CN- ion forms low spin complexes. The electronic

configuration in this case is ��� ��

, predicting possibility of Jahn-Teller

distortion. Consequently octahedral low-spin Co(II) complexes are tending to

lose ligands and form low spin four or five coordinate species.

The octahedral and tetrahedral complexes differ in their magnetic

properties. Because of the intrinsic orbital angular momentum in octahedral

ground state, there is consistently a considerable orbital contribution, and

effective magnetic moments for such compounds around room temperature

are between 4.7 and 5.2 BM. For tetrahedral complexes the ground state

acquires orbital angular momentum only indirectly through mixing with the 4T2 state, by spin-orbit coupling perturbation. This results in greater magnetic

moments than the spin only value of 3.89 BM [33].

1.4 Nickel- General Chemistry

Nickel is a hard silvery white metal, which occurs as cubic crystals.

This metal has high electrical and thermal conductivities. It is quite resistant

to attack by air or water at ordinary temperatures when compact but the

Introduction 13

finely divided metal is reactive to air. The metal is ferromagnetic and

moderately electropositive with a reduction potential of – 0.24 V. It dissolves

readily in dilute mineral acids. Nickel reacts with halogens on heating.

Nickel(II) oxide with rock salt structure is formed by heating hydroxide,

carbonate, oxalate, or nitrate. All nickel dihalides are known to exist.

Preparation of these nickel(II) salts directly from the elements is possible

except NiF2. Most of these salts are soluble in water and crystallization of

hexahydrate containing the [Ni(H2O)6]2+ ion usually occurs in these cases.

Other primary nickel compounds, probably all containing Ni(II) but not all

stoichiometric, may be obtained by the direct reaction of nickel with various

nonmetals such as P, As, Sb, S, Se, Te, C and B.

Nickel has a variety of oxidation states ranging from -1 to +4. The

most common oxidation state is +2. The oxidation number of nickel in

[Ni(CO)6]2- is -1 while it is zero in [Ni(CO)4]. Ni(0) complexes are numerous

and are diamagnetic which show that the ligands stabilize the 3d10

configuration relative to the other ones. The +1 oxidation state of nickel is

shown by [Ni(PPh3)3Br]. [NiBr3(PR3)2] has trigonal bipyramidal structure

with +3 oxidation state. K2[NiF6] is an example of nickel compound with +4

oxidation state. Its geometry is distorted octahedral. All reported Ni3+

complexes have a spin doublet ground state originating from the 3d7 free ion

configuration and are paramagnetic while Ni4+ complexes have a singlet

ground state originating from 3d6 configuration and are diamagnetic.

1.4.1 Nickel(II) - Coordination Chemistry

Nickel(II) forms a large number of complexes with coordination

numbers 3 to 6.

14 Chapter 1

Table 1.3 Various coordination geometries displayed by Nickel(II) complexes

Coordination number Geometry Examples

3 Trigonal planar [Ni(NPh2)3]3-

4 Square planar [Ni(en)2]2+

4 Tetrahedral [Ni(Br)4]2-

5 Square pyramid [Ni(CN)5]3-

5 Trigonal bipyramid [NiBr3(PR3)2]

6 Octahedral [Ni(H2O)6]2+

The maximum coordination number of nickel(II) is 6. In nickel(II)

complexes a temperature dependent equilibrium exist among the various

structures. This is due to small free energy difference between the various

stereochemical forms [34]. Fig. 1.2 shows the d-orbital splitting patterns for

tetrahedral, square planar and octahedral complexes of Ni2+.

Fig. 1.2 d-orbital splitting pattern for tetrahedral, octahedral, tetragonally

distorted and square planar Ni2+.

Introduction 15

Some neutral ligands displace water molecules from [Ni(H2O)6]2+ ion

to form complexes such as trans-[Ni(H2O)2(NH3)4](NO3)2. These complexes

are characteristically blue or purple in contrast to bright green of the

hexaaqua nickel(II) ion. This is because of shifts in the absorption bands

when H2O molecules are replaced by others lying towards the stronger end

of spectrochemical series.

Four coordinate nickel(II) complexes are very common. Good

π-donor ligands such as halides tend to stabilize tetrahedral geometries while

π-acceptor ligands such as CN- favour square planar geometries. Planar

coordination is a natural consequence of the d8 configuration, since the

planar ligand set causes one of the d orbitals (d x2-y

2) to be uniquely high in

energy and eight electrons can occupy the other four d orbitals leaving this

strongly antibonding one vacant. The interconversion of paramagnetic

tetrahedral and diamagnetic square planar geometries is well established [35,

36]. These changes from tetrahedral to square planar geometries are

influenced by the steric effect of the ligands with tetrahedral coordination

which is generally favoured by highly bulky ligands. Square planar nickel(II)

complexes are capable of coordinating extra ligands in solution to set up

equillibria between four, five and six coordinate complexes. Thus

diamagnetic square planar complexes can be transformed into paramagnetic

octahedral nickel(II) species in coordinating solvents or in presence of extra

ligands. These transformations can be monitored by electronic spectroscopy.

A considerable number of both trigonal bipyramidal and square

pyramidal complexes occur with high and low spin. [Ni(Me6tren)Br]+ is a

high spin complex of trigonal bipyramid geometry. [Ni(CN)5]3- ion is usually

found with square pyramidal geometry but in [Cr(en)3][Ni(CN)5].1.5 H2O

there are two crystallographically independent[Ni(CN)5]3- ions, one with

16 Chapter 1

square pyramidal and the other with trigonal bipyramidal geometry.

However when the compound is dehydrated or subjected to pressure, the

crystal structure changes and the trigonal bipyramid becomes square

pyramid.

1.4.2 Nickel(II)- Electronic spectra and Magnetism

The free Ni(II) ion has a d8 configuration and the corresponding

ground state is 3F. Three spin allowed transitions are expected from the

energy level diagram for octahedral d8 ions and the three bands are assigned

as 3A2g(F) → 3T1g(P), 3A2g(F) → 3T1g(F) and 3A2g(F) → 3T2g(F). The

magnetic moment of octahedral complexes is in the range 2.9 to 3.4 BM,

depending upon the magnitude of orbital contribution.

The expected d-d transitions for tetrahedral nickel(II) complexes are 3T1(F) → 3T2 (F), 3T1(F) → 3A2(F) and 3T1(F) → 3T1(P). Tetrahedral

complexes are generally intense blue in colour due to absorption of radiation

from red end of the visible region. The occasional appearance of green or red

colour for tetrahedral complexes of nickel(II) is attributed to charge transfer

absorption tailing in to the visible region from the ultraviolet region [37].

Since the ground state 3T1(F) has intrinsic orbital angular momentum, the

magnetic moment of truly tetrahedral nickel(II) complexes should be 4.2 BM

at room temperature. Fairly regular tetrahedral complexes have moments in

the range 3.5 to 4.0 BM.

The square planar complexes of nickel(II) are generally red, yellow

or brown and are diamagnetic, but recently some paramagnetic planar

nickel(II) species have been reported [38,39]. The expected electronic

transitions are 1A1g → 1B1g and 1A1g→ 1B2g. The vast majority of nickel(II)

Introduction 17

complexes prefer square planar geometry which is a natural consequence of

d8 configuration.

1.5 Copper- General Chemistry

Copper is a reddish coloured metal which is malleable and ductile

and takes a bright metallic lusture. Copper is an important metal and is

extensively used for industrial, agricultural and domestic purposes owing to

its properties of high electrical conductivity, chemical stability, plasticity and

capacity to form alloys with many metals.

Copper has a variety of oxidation states ranging from zero to four.

Copper(I) and copper(II) complexes are common. The relative stabilities of

Cu(I) and Cu(II) states are indicated by the following potential data:

Cu+ + e Cu E° = 0.52 V

Cu2+ + 2e Cu E° = 0.34 V

The relative stabilities of copper(I) and copper(II) in aqueous solution

depend very strongly on the nature of anions or other ligands present and

vary considerably with solvent or the nature of neighbouring atoms in a

crystal. The copper(II) cation may be stabilized by complex formation

against reduction to copper(I) by reducing anions such as iodide and cyanide.

All the copper(I) halides are known to exist although the fluoride has not yet

been obtained in the pure state. The cuprous chloride, bromide and iodide are

colourless and diamagnetic. They crystallize with zinc blende structure in

which copper atoms are tetrahedrally bonded to four halogens. The halides of

copper(II) are colourless CuF2 (with a distorted rutile structure), the yellow

chloride and almost black bromide. Copper(II) halides are moderate

oxidizing agents due to Cu(I)/Cu(II) couple. The relative stabilities of

copper(I) and copper(II) in aqueous solution depend very strongly on the

18 Chapter 1

nature of anions or other ligands present and vary considerably with the

solvent or the neighboring atoms in the crystal.

In aqueous solution, only low equilibrium concentrations of Cu+ can

exist and only simple compounds that are stable in water are highly insoluble

ones such as CuCl or CuCN. This instability toward water is due to the

greater lattice and solvation energies and higher formation constants of

complexes of copper(II) ion, so that copper(I) derivatives are unstable. Of

course numerous copper(I) cationic or anionic complexes are stable in

aqueous solution. The equilibrium 2Cu(I) Cu + Cu(II) can readily be

displaced in either direction. Thus copper(II) reacts with (CN)-, I- and Me2S

to give copper(I) compound [40, 41].

1.5.1 Copper(II)- Coordination Chemistry

Copper(II) complexes show distorted octahedral and tetrahedral

symmetries due to d9 configuration. The distortion is usually seen as axial

elongation consistent with the liability and geometric flexibility of the

complexes. Therefore typical copper(II) complexes have square planar or

square pyramidal geometries with weakly associated ligands in axial

position, but some Cu(II) complexes possess trigonal bipyramidal geometry.

The various geometries and coordination numbers adopted by copper(II) is

given in Table1.4.

Introduction 19

Table 1.4 Various coordination geometries shown by Cu(II) complexes

Coordination number Geometry Examples

3 Trigonal planar [Cu2(µ-Br)2Br2]

4 Tetrahedral Cs2[CuCl4]

4 Square planar [Cu(NH4)2Cl4]

5 Trigonal bipyramid [Cu(NH3)2][Ag(SCN)3]

5 Square pyramid [CuCl5]2-

6 Octahedral [Cu(NH3)4 (SCN)2]

6 Distorted octahedral [Cu(NH3)4(H2O)(SO4)]

7 Pentagonal bipyramid [Cu(H2O)2(dps)]2+

8 Distorted dodecahedron Ca[Cu(CO2Me)4]6H2O

The complexes with coordination numbers four, five and six are

common. Copper(II) complexes are characterized by a variety of distortion

[42, 43]. The majority of six coordinate copper(II) complexes have elongated

tetragonal or rhombic octahedral or compressed tetragonal structures. The

tetrahedral geometry of copper(II) ion always involves significant

compression along the S4 axis. Only square planar copper(II) complexes

have regular structure with small tetrahedral distortion. In five coordinate

system copper(II) ion rarely involves a regular square pyramidal

stereochemistry but generally involves both an elongation and trigonal

inplane distortion. The trigonal bipyramidal stereochemistry of copper(II)

may be regular but is often subjected to distortion towards square pyramidal

geometry.

20 Chapter 1

1.5.2 Copper(II)- Electronic Spectra and Magnetism

Most of the copper(II) complexes are blue or green because of d-d

absorption in the 600-900 nm region. There are exceptions in which there are

strong charge transfer bands tailing in to the visible region causing a red

brown appearance.

Extensive studies have been conducted on the nature of bonding in

copper(II) complexes [44, 45]. The correlation between stereochemistry and

d9 configuration has been well established using single crystal technique,

electronic and EPR spectra [45, 46]. There are numerous cases in which

apparently octahedral copper(II) complexes execute a dynamic Jahn-Teller

behaviour, when the direction of elongation varies rapidly [47]. Since

copper(II) is subjected to Jahn-Teller distortion a regular octahedral complex

is not formed in all the cases. The spectra do not usually correspond to the

simple 2Eg → 2T2g transition [48, 49] but rather to one based upon the

following Fig. 1.3.

Fig.1.3 Splitting of 2Eg and 2T2g states in copper(II)

Four-coordinate copper(II) complexes are common but the strict

tetrahedral or square planar geometries are rare. Some intermediate

stereochemistry of approximate D2d symmetry is more usual and four

Introduction 21

transitions between d orbitals may be available [50]. The spectra of such

complexes show two or three less resolved bands below 500 nm.

The measurement of magnetic susceptibility of copper(II) complex

can give little information. For mononuclear complexes the magnetic

moments are generally in the range 1.75-2.26 BM regardless of

stereochemistry [51] and independent of temperature except at extremely low

temperature. There are a number of polynuclear compounds with anomalous

magnetic behavior [52]. In these compounds there occurs a weak coupling

with unpaired electron on each copper(II) ion. As a result magnetic moment

value will be lowered from normal value.

Applications of Transition Metal Complexes

The area of transition metal complexes got much attention in recent

years due to their extensive applications in wide range. Metal complexes of

Schiff bases have played a central role in the development of coordination

chemistry. The developments in the field of bioinorganic chemistry have

increased the interest in Schiff base complexes because it has been

recognized that many of these complexes serve as models for biologically

important species. Schiff bases of transition metal complexes find

application in biological modelling, catalysis, design of molecular

ferromagnets and material chemistry [53-56]. Cationic metal complexes

possessing planar aromatic ligands may bind to DNA by ligand intercalation,

which involves stacking of planar ligand in between adjacent base pairs of

DNA duplex. Such metallointercalators are particularly useful in probing

DNA structure and function and the intercalation process itself [57]. Certain

metallointercalators, which cleave DNA owing to the redox activity of the

metal centre, have further been successfully employed in foot printing

studies of drug binding and in the examination of charge transport through

22 Chapter 1

DNA [58, 59]. 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 and linear polyethylenes [60,

61]. The oxidation of hydrocarbons using Schiff base complexes has been a

field of academic and industrial interest to analyze the catalytic activity of

various metal complexes [62, 63].

Some Schiff bases of transition metals are used as blue luminescent

materials [64]. Among them some complexes are found to have excellent

light emitting and charge transforming properties. The applications of Schiff

base complexes in full color flat-panel displays are pointed out by

experimental reports as light emitting materials [65]. The ability of transition

metal complexes to tailor metal-organic interactions and various oxidation

states of metals present in such systems makes these complexes as potential

building blocks for non-linear optical materials [66, 67]. Good second order

non-linear optical (NLO) properties are reported in some Schiff base

complexes [68, 69].

Leathers, food packages, wools and polyfibers can be fastly coloured

with azomethine complexes of some transition metals [70]. Some natural

food samples are analyzed for the presence of nickel by using novel

tetradentate Schiff bases which are used as chromogenic agents [71]. The

copolymerization of dienyl and vinyl monomers and emulsion

polymerization are usually initiated by organocobalt complexes with

tridentate Schiff bases [72].

Many Schiff base complexes show catalytic activity. Some of them

are found to act as good catalysts for the polymerization of olefins. Schiff

base complexes can act as catalysts in the synthesis of commercially

Introduction 23

important branched and linear polyethylenes [73 - 75]. The Schiff base

complex catalysed ring opening polymersation of cycloalkanes at low

temperature provided a control over molecular weight of polymer without

any side reaction [76, 77]. The oxidation of hydrocarbons using Schiff base

complexes has been a field of academic and industrial interest to analyze the

catalytic activity of various metal complexes [78]. Schiff base complexes

show significant application in reduction of ketones to aldehydes and

alkylation of allylic substrates [79, 80]. The Heck reaction, an industrially

useful process to synthesize fine chemicals and pharmaceuticals, was

successfully catalysed using Schiff base complexes [81]. Schiff base

complexes are potential catalysts to influence the yield and selectivity in

chemical transformations. Coordination complexes containing

ferromagnetically and ferrimagnetically organized paramagnetic metal ions

are of interest for their potential to act as Single Molecule Magnets (SMMs).

At low temperatures (typically below 5K), a SMM subjected to a magnetic

field will remain magnetized for a period of time after removal of the

magnetic field. This property may ultimately lead to applications of SMMs

in dense nano-scale data storage [82].

Miniaturization towards nanoscopic and molecular scales is one of

the most pursued targets in modern science and for future developments in

industry. One of the topics is molecular switching between physically or

chemically induced electronic spin states in coordination compounds, which

includes spin cross over effects. Spin cross over is the most appealing

molecular effects in iron coordination compounds [83, 84]. In iron(III) Schiff

base compounds, the pentadentate ligand forms the pseudo-octahedral

building blocks [Fe(5L)X] (with X as a monodentate ligand and L as

pentadentate ligand) with a number of interesting electronic and structural

24 Chapter 1

features. This class of compounds often shows thermally induced transition

between low-spin and high-spin states [85]. In these compounds, the selected

ligand design allows us to gain a switching effect that follows a sequential

and concerted mechanism.

Several Cu(II) Schiff base complexes have been subject of intense

investigation for DNA binding and cleavage studies [86 - 88]. It has been

demonstrated that copper accumulates in tumors due to selective

permeability of cancer cell membranes [89]. Because of this, a number of

copper complexes have been screened for anticancer activity and some of

them found active both in vivo and in vitro [90]. Cu(II) Schiff base

complexes are used as mediators in atom transfer radical cyclisation

reactions. Copper Schiff base catalysts are used in carbon based radical

cyclisation reactions [91].

Further research and developments in the area of Schiff base

complexes of transition metal ions would be highly useful in industries and

academia.

Review of Studies on Fe(III), Co(II), Ni(II) and Cu(II) Complexes

with Derivatives of Pyrazolones and Chromones

A novel bidentate Schiff base has been synthesized from 1-phenyl

2,3-dimethyl-4-aminopyrazol-5-one and vanillin [92]. Its transition metal

complexes with Mn(II), Cr(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)

were also synthesized and characterized. The complexes have formulae

[M(L) 2(H2O)2]Cl3 (where M = Cr(III)), [M(L)2(H2O)2]SO4 (where

M = Mn(II), Ni(II) or Zn(II)) and [M(L)2(H2O)2]Cl2 (where M = Co(II),

Cu(II) or Cd(II)). The Schiff base acts as a bidentate ligand in all the

Introduction 25

complexes. All the complexes have an octahedral geometry around metal

center.

The Cu(II), Ni(II), Co(II), Mn(II), Zn(II) and VO(IV) complexes of

the Schiff base 1,2-(diimino-4′-antipyrinyl)-1,2-diphenylethane (L) has been

synthesized and characterized [93]. The complexes have the formulae

[CuLCl2], [CuL(OAc)2], [CuL(Py)2]Cl2, [CuL(Py)2](OAc)2, [NiLCl2],

[NiL(OAc)2], [CoLCl2], [CoL(OAc)2], [MnLCl2], [MnL(OAc)2] and

[VOL]SO4. All the complexes have an octahedral geometry, except VO(IV)

complex which has a square pyramidal geometry around the central metal ion.

3-carbaldehyde-chromone semicarbazone (L) and its Cu(II), Zn(II),

Ni(II) complexes were synthesized and characterized [94] on the basis of

crystal structure and other structural characterization methods. The Schiff

base acts as a tridentate ligand in the complexes and form mononuclear five

coordination complexes with trigonal bipyramidal geometry around central

metal ion. The nitrate molecules were monodentately coordinated with

central metal ion in all the complexes. The complexes were found to have the

formulae [Cu(L)(NO3)2], [Zn(L)(NO3)2] and [Ni(L)(NO3)2] .

Cu(II), Ni(II),Co(II), Mn(II), VO(IV) and Zn(II) complexes of Schiff

bases salicylidene-4-aminoantipyrinyl-2-aminophenol (H2L1) and salicylidene-

4-aminoantipyrinyl-2-aminothiophenol (H2L2) have been synthesized and

characterized [95]. The Schiff bases behave as tetradentate in these

complexes. All the complexes are of square planar geometry, except Mn(II)

and VO(IV) complexes for which an octahedral and a square pyramidal

geometry respectively around central metal ion.

The Schiff base ligand 2-[(4-oxo-4H-chromen-3yl)methylamino]

benzoic acid (L) and a series of metal complexes comprising of Cu(II),

26 Chapter 1

Co(II), Ni(II), Mn(II) and Zn(II) were synthesized and characterized [96].

The Schiff base acts as a tridentate ligand in the complexes. The complexes

have the general formula [ML2] (where M = Cu(II), Co(II), Ni(II), Mn(II) or

Zn(II)) with an octahedral geometry around the metal ion in all the

complexes.

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived

from vaniline-4-aminoantipyrine and O-phenylenediamine were synthesized

and characterized [97]. The complexes have formula [MLCl 2] (where M =

Co(II), Ni(II), Cu(II) or Zn(II)). The Schiff base act as tetradentate ligand in

all the complexes and the complexes have an octahedral geometry around

metal center.

The Cr(III), Co(II), Fe(III) and Zn(II) complexes of Schiff bases derived

from 6-formyl-5,7-dihydroxy-2-methylbenzopyran-4-one and ethylenediamine

(H4La) or propylenediamine (H4Lb) were synthesized and characterized [98].

The complexes have the formulae [CrH2La(OH)(H2O)].3H2O,

[FeH2La(OH)(H2O)].3H2O, [CoH2La(H2O)2].4H2O, [CrH2LbCl(H2O)].3H2O,

[FeH2Lb(OH)(H2O)].5H2O and [CoH2Lb(H2O)]ClO4.2H2O. The Zn(II)

complexes have a square planar geometry, while Cr(III), Fe(III) and Co(II)

complexes have an octahedral geometry around metal ion.

Neutral complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Cd(II),

Hg(II), VO(II), ZrO(II) and UO2(II) with Schiff base acetoacetanilido-4-

aminoantipyrine (L) have been synthesized and characterized [99]. The

complexes have the general formula [ML2] (where M = Cu(II), Ni(II),

Co(II), Mn(II), Zn(II), Cd(II), Hg(II), VO(II), ZrO(II) or UO2(II)). All

complexes have an octahedral geometry except [VOL2] which has a square

pyramidal geometry, around central metal ion.

Introduction 27

(2z,2′z)-4,4′-(1E,1′E)-1,2-diphenylethane-1,2-1,2-diylidene)bis(azan-

1-yl-1-ylidene)bis(1,5-dimethyl-2-phenyl-1-H-pyrazole-4(2H)-yl-3(2H)-ylidene)

bis(hydrazinecarbothioamide) (L) and its Co(II), Ni(II), Cu(II) and Zn(II)

complexes were synthesized and characterized [100]. The complexes have

formula [M(L)]Cl2.H2O (where M = Co(II), Ni(II), Cu(II) or Zn(II)). All the

complexes except Cu(II) complex show octahedral geometry around central

metal ion, while Cu(II) complex shows square-planar geometry around

central metal ion.

2-(N-3-formylchromone)iminothiazole (HL) and its Co(II), Cu(II),

Zn(II) and VO(IV) complexes were synthesized [101] and characterized. The

complexes have the general formula [MLCl] (where M = Co(II), Cu(II) or

Zn(II)) and [VOLCl]. The Cu(II) complex shows tetrahedrally distorted

square planar, Co(II), Ni(II), Zn(II) show distorted tetrahedral and VO(IV)

complex shows square pyramidal geometry around central metal ion.

Complexes with formulae [CuLCl(H2O)], [CuL(NO3)(H2O)2],

[CuL2], [CuL(SCN)(H2O)2], [CuL(ClO4)(H2O)2] and [CuL2(H2O)4]SO4

(where HL = 1-phenyl-2,3 –dimethyl-4-(N-2-hydroxy-benzaldehyde)3-

pyrazolin-5-one) have been synthesized and characterized [102]. The Schiff

base was tetradentately coordinated to metal ion in all the complexes.

[CuLCl(H2O)] has trigonalbipyramidal geometry while all other complexes

have tetragonal geometry around central metal ion.

Mixed ligand cobalt(II) complexes of Schiff bases L1 = 2,3–

dimethyl-1-phenyl-4-(3-ethoxy-2-hydroxybenzylideneamino)-pyrazol-5-

one, L2 = 2,3–dimethyl-1-phenyl-4-(-2-hydroxy-3-methoxy benzylideneamino)-

pyrazol-5-one, L3=2,3–dimethyl-1-phenyl-4-(-2-hydroxy-5-nitro benzylideneamino)-

pyrazol-5-one, L4 = 2,3–dimethyl-1-phenyl-4-(5-chloro-2-hydroxybenzylideneamino)-

28 Chapter 1

pyrazol-5-one, L5 = 2,3-dimethyl-1-phenyl-4-(5-bromo-2-hydroxybenzylideneamino)-

pyrazol-5-one and 2,2 –bipyridine(bpy) were synthesized and characterized

[103]. The complexes have general formula [CoL(bpy)(H2O)]+ (where

L = L1, L2, L3, L4 or L5). All the complexes have an octahedral geometry

around the central metal ion.

A new Schiff base formed by the condensation of 4-aminoantipyrine,

3-hydroxy-4-nitrobenzaldehyde and O-phenylenediamine (L) and its

complexes with Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV), Hg(II) and

Cd(II) have been synthesized [104] and characterized. In all the complexes

the Schiff base acts as a tetradentate ligand coordinating through four

nitrogens. The complexes have the general formula [ML]Cl 2 (where

M = Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV), Hg(II) or Cd(II)). All the

complexes have square planar geometry except for VO(IV) which have

square pyramidal geometry around central metal ion.

Copper(II) complexes of four different Schiff bases 3-

(hydroxyphenylimino)methyl-4H-chromen-4-one (HL1), 2-[(4-oxo-4H-

chromen-3-yl)methyleneamino]benzoic acid (HL2), 3-[(3-hydroxypyridin-2-

ylimino)methyl]-4H-chromen-4-one (HL3) and 3-[(2-mercaptophenylimino)

methyl]-4H-chromen-4-one (HL4) have been synthesized and

characterized[105]. The complexes have formulae [Cu(L1)2]2H2O,

[Cu(L2)2]H2O, [Cu(L3)2] and [Cu(L4)2]. The ligands coordinated to copper(II)

ion in tridentate manner and geometrical structures of these complexes are

tetragonally distorted octahedral.

1-phenyl-2,3-dimethyl-4-(N-3-formyl-6-methyl chromone)-3-pyrozolin-

5-one (L) and its Cu(II), VO(II), Ni(II) and Mn(II) complexes were

synthesized and characterized [106]. The complexes have formulae

Introduction 29

[Cu2L2Cl2](1), [Cu L(NO3)] (2), [Cu L(OAc)]CH3OH (3), [CuL(SCN)] (4),

[CuL(H2O)]ClO4 (5), [Cu 2L2(H2O)4]SO4 (6), [NiL2] (7), [VOL2] (8) and

[MnL2] (9). In all the complexes the ligand acts as a mononegative tridentate

around metallic ion except in 8 in which it acts as mononegative bidentate.

The complexes 2, 3, 4 and 5 are found to have distorted square planar, 1 and

8 have square pyramidal and 6, 7 and 9 have an octahedral geometry around

the metal ion.

A new Schiff base 6-hydroxychromone-3-carbaldehydethiosemicarbazone

(L) and its Ni(II) complex have been synthesized and characterized [107].

The ligand is coordinated in a tridentate manner to metal ion. The complex

[Ni(L)(H 2O)3]NO3.2H2O has a distorted octahedral geometry around central

metal ion.

Two new chromone based Schiff base ligands 3-{[(1,5-dihydro-3-

methyl-5-thioxo-4H-1,2,4-triazol-4-yl)imino]methyl}-6-hydroxy-4H-1-

benzopyran-4-one (L1) and 2,2’-bis[(6-hydroxy-4-oxo-4H-1-benzopyran-3-

yl)methylene]carbonothionic dihydrazide(L2) and their Ni(II) and Zn(II)

complexes were synthesized and characterized [108]. The results suggest that

the complexes have formulae [NiL1H2O](NO3)2.H2O and [ZnL1(H2O)3]

(NO3)2.0.5 H2O and [ML22](NO3)2 (M = Ni(II) or Zn(II)). The Schiff base

ligands were tridentately coordinated to metal ion in the complexes.

[NiL 1H2O](NO3)2.H2O has a tetrahedral geometry while all other complexes

have octahedral geometry around metal center.

The coordination complexes of VO(II), Co(II), Ni(II) and Cu(II) with

the Schiff bases isatin-3-chloro-4-fluoroaniline (A) and 2-pyridine

carboxylidene-4-aminoantipyrine (B) were synthesized [109] and characterized.

The complexes have formulae [VO(A)2]SO4 (1), [Co(A)2]Cl2 (2),

30 Chapter 1

[Ni(A) 2(H2O)2]Cl2.H2O (3), [Cu(A)2]Cl2 (4), [VO(B)(H2O)]SO4.3H2O (5),

[Co(B)Cl]Cl.H2O (6), [Ni(B)Cl]Cl.3H2O (7) and [Cu(B)Cl]Cl.H2O (8). The

complexes 1 and 5 have trigonal bipyramidal, 2 and 6 have tetrahedral, 3

has octahedral and 4, 7 and 8 have square planar geometry around central

metal ion.

The Schiff base 3-salicylidene-2,4-di(imino-4′-antipyrinyl)pentane

(L) and its Cu(II), Ni(II), Co(II) and Zn(II) complexes were synthesized and

characterized [110]. The complexes have general formula [ML]Cl2.xH2O

(where M = Cu(II), x = 2; M = Ni(II), x = 6; M = Co(II), x = 6 and M =

Zn(II), x = 2). The Schiff base acts as tetradentate ligand and the geometry

around central metal ion is square planar in all the complexes.

Cu(II), Ni(II), Co(II), Zn(II), Fe(III) and VO(IV) complexes of a Schiff

base ligand 2,3-dimethyl-1-phenyl-4-(5-nitro-2-hydroxybenzylideneamino)-

pyrazol-5-one (L) have been synthesized and characterized [111]. The Schiff

base acts as tridentate ligand and the complexes have formulae [M(L)2]H2O

(where M = Cu(II), Ni(II), Co(II) or Zn(II)), [VO(L)2H2O] and [Fe(L)2H2O].

All the complexes have octahedral geometry around central metal ion.

Complexes with formulae [Cu(L1)2] and [Cu(L2)2] (where L1 = 4-{[(1-

Z)-(2,4-dihydroxyphenyl)methylene]-amino}-1,5-dimethyl-2-phenyl-1,2-

dihydro-3H-pyrazol-3-one and L2 = 4-{[(1Z)-3,5-dichloro-2-hydroxyphenyl)

methylene]amino}-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one) were

synthesized and characterized [112]. The Schiff bases act as bidentate ligands

in complexes and the complexes have a distorted square planar geometry

around central metal ion.

Complexes of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and

UO2(VI) with N-(4-formylantipyrine)benzothiazole-2ylacetohydrazide were

Introduction 31

synthesized and characterized [113]. The Schiff base acts as a monobasic

tridentate ligand in complexes. The geometry around central metal ion is

octahedral for iron(III) complexes, tetrahedral for Mn(II), Co(II), Ni(II),

Cu(II) and Zn(II) complexes and square planar for Cu(II) complexes.

3(3′-hydroxy-4′-nitrobenzalidene)-2,4-di(imino-4′′-antipyrinyl)pentane

(L) and its Copper(II), Nickel(II), Zinc(II) and VO(IV) complexes were

synthesized and characterized [114]. The Schiff base acts as a tetradentate

ligand in all the complexes and the complexes have formulae [CuL]Cl2,

[Ni(L)]Cl 2, [VO(L)]SO4 and [Zn(L)]Cl2. All the complexes have square

planar geometry except [VO(L)]SO4 which has square pyramidal geometry

around central metal ion.

A novel Schiff base sodium salt 6-hydroxychromone-3-

methylidyneiminoacetate (LNa) and its complexes [CuL(H2O)3]NO3.H2O

and [NiL(H2O)]NO3.2H2O have been synthesized and characterized [115].

The Schiff base acts as a tridentate ligand in the complexes and geometry

around central metal ion is octahedral in Cu(II) complex and tetrahedral in

Ni(II) complex.

A Schiff base 4-hydroxy-3-methoxybenzylidine-4-aminoantipyrine

(HL) and its complexes with Cu(II), Ni(II), Co(II) and Zn(II) have been

synthesized and structurally characterized [116]. The complexes have

general formula [ML2] (where M = Cu(II), Ni(II), Co(II) or Zn(II)). The

Schiff base behaves as a tridentate ligand in the complexes and the

complexes have an octahedral geometry around central metal ion.

Co(II), Ni(II), Cu(II) and Zn(II) complexes of Schiff bases N′-[(E)(2-

hydroxyqunolin-3-yl)methylidene]-2-[(4-methyl-2-oxo-2H-chromen-7-

yl)oxy]acetohydrazide (L1) and 2-((4-methyl-2-oxo-2H-chromen-7-yloxy]-

32 Chapter 1

N′-[(E)-(2-sulphanylquinolin-3-yl)methylene (L2) have been synthesized and

characterized [117]. The complexes have general formula [ML2] (where

M = Co(II), Ni(II), Cu(II) or Zn(II) and L = L1 or L2). All the complexes

have an octahedral geometry around central metal ion.

Complexes of Cu(II), Ni(II), Co(II) and Mn(II) were synthesized from

PB (a Schiff base derived from 6-formyl-5,7-dihydroxy-2-methyl benzopyran-4-

one and 2- aminopyridine) [118]. The complexes have formulae

[Mn(PB)Cl(H2O)3]H2O, [Co(PB)(OAc)(H2O)3]H2O, [Ni(PB)(OH)(H2O)3]2H2O

and [Cu(PB)(OAc)H2O]2H2O. The Schiff base behaves as mononegative

bidentate ligand in the complexes. A square planar structure has been

proposed for Cu(II) complex and all other complexes are in an octahedral

environment around metal ion.

Two new Schiff base ligands H2La and H2Lb were synthesized by

condensation of ethylenediamine and trimethylene diamine respectively with

6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-one. The metal

complexes of H2La and H2Lb with metal ions Cr(III), Fe(III), Co(II), Ni(II),

Cu(II) and Zn(II) were synthesized and characterized [119]. The Schiff bases

have coordinated to metal ion in a tetradentate mode. The Cu(II), Zn(II), and

Ni(II) (for H2La) complexes have square planar geometry and Co(II), Cr(III),

Fe(III) and Ni(II) (for H2Lb) have an octahedral geometry around central

metal ion.

Cu(II), Ni(II), Co(II), Mn(II), Mn(II), Hg(II) and Sn(II) complexes of

4-(4-fluorobenzylidineamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-

one (FAPPO) have been synthesized and characterized [120]. The complexes

have formula [M(FAPPO)2] (where M = Cu(II), Ni(II), Co(II), Mn(II),

Mn(II), Hg(II) or Sn(II)). The Schiff base is bidentately coordinated to metal

Introduction 33

ion in complexes and all the complexes have a square planar geometry

around central metal ion.

A series of metal complexes of VO(II), Co(II), Ni(II), Cu(II) and

Zn(II) have been synthesized from azo Schiff base ligand 4-((E)-4-((E)-(4-

chlorophenyl)diazenyl)-2-hydroxybenzylideneamino)-1,5-dimethyl-2-phenyl-

1H-pyrazol-3(2H)-one (CBHBAP) and were characterized [121]. The

complexes have formula [M(CDHBAP)Cl(H2O)2] (where M = Co(II), Ni(II),

Cu(II) or Zn(II)) and [VO(CDHBAP)Cl]. CBHBAP was coordinated to

metal ion in a neutral tridentate manner. VO(II) complex has a square

pyramidal geometry and all other complexes have octahedral geometry

around central metal ion.

Cu(II), Co(II), Ni(II), Zn(II), Mn(II), Cd(II) and VO(II) complexes of

Schiff base derived from 3-(3-(2-hydroxyphenyl)-3-oxoprop-1-enyl)4H-

chromen-4-one and sulphanilamide have been synthesized and characterized

[122]. The complexes have formula [MLCl2(H2O)2] (where M = Cu(II),

Co(II), Ni(II), Zn(II), Mn(II) or Cd(II)) and [VOL(H2O)2]SO4. Oxovanadium

complex has a square pyramidal geometry and all other complexes have

octahedral geometry around central metal ion.

The complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with

3-(anilinomethylene)-2-methoxychroman-4-one (L) have been synthesized

and characterized [123]. The Schiff base acts as a bidentate ligand in all the

complexes. The complexes have general formula [ML2Cl2] (where M = Mn(II),

Cu(II) and Zn(II)) and [ML2Cl(H2O)] (where M = Co(II) and Ni(II)). All the

complexes have octahedral geometry around central metal ion.

Some novel iron(III) complexes of formulae [FeL1(X)3], [FeL1(Y)(X)2],

[Fe(L1)2(Z)X]Z, [Fe(L2)2(X)2], FeL2(X)3(H2O)], [FeL2(Y)2(H2O)X],

34 Chapter 1

[FeL2(Z)3(H2O)] and [Fe2(L2)2(X)6] (where L1 = guaiacolazo antipyrine, L2 = 3-

methoxy phenol azo antipyrine; X = Cl/Br/NO3; Y = NCS; Z = ClO4) have been

synthesized and characterized [124]. The complexes have an octahedral

geometry around central metal ion.

Azo Schiff base complexes of VO(II), Co(II), Ni(II), Cu(II) and Zn(II)

with 3-(4-(5-(4-chlorophenyl)diazenyl)-2-hydroxybenzylideneamino)

Phenylimino)methyl)-4-H-Chromen-4-one (L) were synthesized and

characterized [125]. The complexes have formulae [ML2Cl2] (where M = Co(II),

Cu(II) or Zn(II)) and [VOL2]). All the complexes have octahedral geometry

except [VOL2] has square pyramidal geometry around central metal ion.

Complexes of Copper(II), Nickel(II), Cobalt(II), Zinc(II) and VO(IV)

with 5-bromosalicylidene-4-aminoantipyrine (5BrSALAAP) have been

synthesized and characterized [126]. The complexes may be represented by

formula [M(5Br SALAAP)2]H2O (where M = Cu(II), Zn(II) or VO(IV)). The

Schiff base is tridentately coordinated in complexes and the complexes have

an octahedral geometry around central metal ion.

N-(1,3-diphenyl-4-benzal-5-pyrazolone)salicylidenehydrazone (H2L′)

and its Zn complex Zn(HL′)22CH3OH have been synthesized and

characterized [127]. The Zn(II) is coordinated by two oxygen and two

nitrogen atoms from two monoanionic bidentate ligands HL′ and two

oxygen atoms of two methanol molecules. The coordination geometry

around Zn(II) ion is slightly distorted shortened octahedron.

Mn(II), Co(II), Ni(II), Cu(II) and Pd(II) complexes of Schiff base, 6-

methyl-3-{[4-(methylsulphanyl)phenyl]imino}methyl]-3,4-dihydro-2H-

chromen-4-ol (L) have been synthesized and characterized [128]. The Schiff

base bidentately coordinates to metal ion in all the complexes. All the

Introduction 35

complexes have the composition [ML2]3H2O except the Mn(II) complex

which has the composition [MnL(NO3]H2O. A four coordinate tetrahedral

geometry is assigned to Mn(II), Co(II), Ni(II) and Zn(II) complexes while a

square planar geometry is assigned to Cu(II) and Pd(II) complexes.

Complexes of 3-(antipyrilidene)salicylic acid (H2L) with Cu(II), Co(II),

Ni(II) and UO2(IV) have been synthesized and characterized [129]. The

Schiff base behaves as a tetradentate ligand in complexes and the complexes

have formula [ML(H2O)2] (where M = Cu(II), Co(II), Ni(II) or UO2(IV)).

All the complexes have an octahedral geometry around central metal ion.

The Cu(II) complex of the Schiff base 5-methyl-1-(pyridine-2-yl)-N′-

[pyridiin-2-ylmethylidene]pyrazole-3-carbohydrazide (L) has been synthesized

and characterized [130]. The complex has formula [Cu(L)NO3(H2O)](NO3) in

which the Schiff base acts as a neutral tetradentate ligand. The complex has a

distorted octahedral geometry.

(E)-2-((3-(3-nitrophenyl)-1-Phenyl-1H-pyrazol-4-yl)methyleneamino)

phenol and its complexes with Cu(II), Co(II) and Ni(II) acetates have been

synthesized and characterized [131]. The complexes have the general

formula [M(L)2(H2O)2] (M = Cu(II), Ni(II) or Co(II)). All the complexes

have octahedral geometry around metal center.

Copper(II), iron(II), cobalt(II, III), nickel(II), chromium(III) and

zinc(II) complexes of 2-methoxy-6-formylchromone thiosemicarbazone

(H2L1), 2-methyl-5,7-dimethoxy-6-formylchromone thiosemicarbazone (HL2)

have been synthesized and characterized [132]. The complexes may be

represented as [Cu(L1)(H2O)]H2O, Fe(L1)(H2O)2Cl2, [Co(L1)(H2O)3]Cl.2H2O,

[Ni(L 1)(H2O)]3H2O, [Cr(HL1)Cl]3H2O, [Zn(L1)H2O]3H2O, [Cu(L2)2]5H2O and

[Co(L2)(H2O)3Cl]4H2O. Fe(III), Co(II), Co(III) and Cr(III) complexes have an

36 Chapter 1

octahedral geometry whereas Cu(II) complex has a square planar geometry

around central metal ion.

Transition metal complexes of Co(II), Ni(II) and Cu(II) with

formulae [M(L)X]X and [M(L)SO4] (where M = Co(II), Ni(II) or Cu(II));

L = 3,3′-thiodipropionic acid bis(4-amino-5-ethylimino-2,3-dimethyl-1-

phenyl-3-pyrazoline ; X = NO3-, Cl- or OAc-) have been synthesized and

characterized [133]. The Ni(II) complexes have octahedral geometry and Co(II)

and Cu(II) complexes have tetragonal geometry around central metal ion.

The Cu(II) complexes of Schiff base 2,3-dimethyl-1-phenyl-4-(2,5-

dihydroxyacetophenone)-5-pyrazolone (L) have been synthesized and

characterized [134]. The complexes have formulae [Cu(L)2Cl2], [Cu(L)2(NO3)2],

[Cu(L)2(ClO4)2], [Cu(L)2(CH3COO)2] and [Cu(L)2(SCN)(Cl)]. The Schiff base

exhibits a neutral bidentate behaviour in complexes and the complexes have

an octahedral geometry around central metal ion.

Two new complexes [M(L)Cl(H2O)2]H2O (where M = Ni(II) or

Ru(II) and L = 3-hydroxy quinoxalin-2-carboxalidene-4-aminoantipyrine)

have been synthesized and characterized [135]. The Schiff base tridentately

coordinates to metal in the complexes and the complexes have distorted

octahedral geometry around central metal ion.

Cu(II), Ni(II) and Co(II) complexes of 2,3-dimethyl-1-phenyl-4-(5-

chloro-2-hydroxybenzylideneamino)-pyrazole-5-one (5-ClSALAAP) and

2,3-dimethyl-1-phenyl-4-(3-ethoxy-2-hydroxybenzylideneamino)-pyrazole-

5-one (3-OEtSALAAP) have been synthesized and characterized [136]. The

Schiff bases coordinates to metal ion in tridentate mode. The complexes have

formula [M(L)2] (where M = (Cu(II), Ni(II) or Co(II)) and L = (5-ClSALAAP)

Introduction 37

or (3-OEtSALAAP)). The complexes have a distorted octahedral geometry

around central metal ion.

N′-[phenyl-5-pyrazolyl)methyledene]pyridine-4-carbodihydrazide(L)

and Co(II), Ni(II) and Cu(II) complexes of this neutral bidentate ligand were

synthesized using acetates, chlorides and nitrates of metals [137]. The

complexes were characterized by different physicochemical methods. The

Copper(II) complex has formula [CuL2Cl2]H2O while all other complexes

have general formula [ML2X2] (M = Co(II), Ni(II) or Cu(II) and X = CH3-

COO-, I-, and NO3-). All the complexes were found to have octahedral

geometry around central metal ion.

Two Schiff base ligands have been synthesized by the condensation

of aminoantipyrine with 2-hydroxy-3-formylquinoline (L1H) and isatin (L2)

respectively. The Cu(II), Ni(II), Co(II) and Zn(II) complexes of these ligands

were synthesized and structurally characterized [138]. The ligand coordinates

to the metal ion in a tridentate manner. The complexes may be represented as

[M(L 1)2(H2O)2] and [ML2Cl2(H2O)2] (where M = Cu(II), Ni(II), Co(II) or

Zn(II)) . All the complexes have octahedral geometry around central metal ion.

Cu(II) complexes have been synthesized from Schiff base ligands

derived from furylidene-4-aminoantipyrine and aniline (L1) / p-nitroaniline

(L2)/ p-hydroxyaniline (L3) and were characterized [139]. The complexes

have formulae [Cu(L)(OAc)2] (where L = L1, L2 or L3). All the complexes

exhibit square planar geometry around central metal ion.

Cu(II) complexes of Schiff bases 1-phenyl-2,3-dimethyl-4-(N-

salicylidene)-3-pyrazolin-5-one (ASAAP) and bis(1-phenyl-2,3-dimethyl-3-

pyrazolin-5-one-4-imino)terephthalic aldehyde (ATAAP) have been

synthesized and characterized [140]. ASAAP acts as tridentate while

38 Chapter 1

ATAAP act as bidentate ligand in complexes. The complexes have formulae

[Cu(ASAAP)(H2O)2]Cl (1) and [Cu(ATAAP)(SO4)2] (2). Complex 1 has

square pyramidal geometry and 2 has distorted tetrahedral geometry around

central metal ion.

A series of transition metal complexes of Fe(III), Co(II), Cu(II) and Ni(II)

with the Schiff base 4-(1-4-{hydroxy-3-methoxybenzylideneamino}phenyl)

ethyledeneamino-1- pyrazole-3-one (L) have been synthesized and

characterized [141]. The complexes have formulae [Fe(L)2Cl2]Cl,

[Co(L)2Cl2]H2O, [Ni(L)Cl2] [Cu(L)2Cl2]H2O. The Schiff base acts as a

bidentate ligand in complexes and all the complexes have octahedral

stereochemistry around central metal ion.

A series of Cu(II), Ni(II) and Co(II) complexes have been

synthesized from 3-formylchromoniminopropylsilatrane (L1) and 3-

formylchroiminopropyltriethoxysilane (L2) [142]. The complexes may be

represented as [M(L)2]Cl2 (Where L = L1 or L2, M = Cu(II), Ni(II) or Co(II)).

The ligands coordinate bidentately to metal ion and the copper and nickel

complexes have square planar while cobalt complexes have tetrahedral

coordination geometries around central metal ion.

3,4-dimethoxybenzylidene-4-aminoantipyrinyl-4-aminomethyl phenol(L)

and a series of transition metal complexes of the type [ML2Cl2](where

M = Cu(II), Ni(II), Co(II) or Zn(II)) have been synthesized and characterized

[143]. Schiff base ligand coordinates bidentately in complexes. The complex

around Cu(II) ion is distorted octahedral and around Ni(II), Co(II) and Zn(II)

ions is octahedral in nature.

Neutral complexes of Co(II), Ni(II), Cu(II) and Zn(II) with Schiff

bases derived from 3-nitrobenzylidene-4-aminoantipyrine and aniline (L′)/p-

Introduction 39

nitroaniline (L2) /p-methoxyaniline (L3) were synthesized and characterized

[144]. The Schiff bases behave as bidentate ligands in complexes and

complexes have formula [ML(OAc)2] (where M = Cu(II), Ni(II), Cu(II) or

Zn(II) ; L = L1, L2 or L3). All the complexes have square planar geometry

around central metal ion.

Cu(II), Ni(II), Co(II), Zn(II) and VO(IV) complexes of Schiff

base derived from 1,2-(diimino-4′-antipyrinyl)-1,2-diphenylethane and

o-phenylenediamine (L) have been synthesized and characterized [145]. The

Schiff base coordinates tetradentately to metal ion in complexes. The

complexes [CuL]Cl2 and [ZnL]Cl2 exhibit square planar geometry,

[CuL(Y)2]Cl2 (where Y = pyridine, imidazole or triphenylphosphine) exhibit

octahedral geometry and [VOL]SO4 exhibit square pyramidal geometry

around central metal ion.

Piperinomethyl antipyrine (PMA) and its Fe(III), Co(II), Cu(II),

Zn(II) and Hg(II) complexes were synthesized and characterized [146]. PMA

acts as a bidentate ligand in complexes. The Fe(III) and Cu(II) complexes

have octahedral geometry and Co(II), Zn(II) and Hg(II) complexes have

tetrahedral geometry around central metal ion.

The Co(III) and Fe(III) complexes of Schiff bases N-(3-methyl-1-

thiocarbamyl-5-oxo-2-pyrazolin-4-ylene)-N′-(4′-antipyrine)hydrazine (L1) and

N-(3-methyl-1-thiocarbamyl-5-oxo-2-pyrazolin-4-ylene)-N′-(4′-benzothiazole)

hydrazine (L2) have been synthesized and characterized [147]. The complexes

have formulae [Co(L1)Cl3], [Co(L1)(NO3)3], [Co(L1)(OAc)3], [Fe(L2)Cl3],

[Co(L2)(NO3)3] and [Co(L2)(OAc)3]. All complexes have an octahedral

geometry around metal(III) center.

40 Chapter 1

Cu(II), Ni(II) and VO(II) complexes of Schiff base formed by the

condensation of aminoantipyrine with 1H-indol-3- carbaldehyde (L) have been

synthesized and characterized [148]. The complexes have formulae [Cu(L)2],

[Cu(L)2](NO3)2, [Cu(L)2(OAc)2], [Cu(L)2(H2O)2]SO4, [VO(L)2(H2O)]SO4 and

[Ni(L) 2(H2O)2]Cl2. Geometry around central metal ion is octahedral in all the

complexes.

Complexes of Fe(III), Co(II), Cu(II) and Ni(II) were synthesized from 4-

(1-4-(hydroxyl-3-methoxybenzylideneamino)phenyl)ethylideneamino)-

1-pyrazole-3-one (L) and were characterized [149]. Schiff base behaves as a

bidentate ligand in the complexes. The complexes have formulae [Fe(L)2Cl2]Cl,

[Co(L)2Cl2]H2O, [Ni(L)Cl2] and [Cu(L)2Cl2]H2O. All the complexes have an

octahedral geometry around central metal ion.

The Cu(II), Ni(II), Co(II) and Zn(II) complexes of bidentate Sciff

base ligand derived from vanillin and 4-aminoantipyrine (L) have been

synthesized and characterized [150]. The complexes have general formula

[ML(OAc)2] (where M = Cu(II), Ni(II), Co(II) or Zn(II)). The Cu(II)

complex has square planar geometry while Ni(II), Co(II) and Zn(II)

complexes have tetrahedral geometry around central metal ion.

Transition metal complexes of an NO donor Schiff base 2-[{3-(4-

fluorophenyl)-1-phenyl-1H-pyrazol-4-yl}methyleneamino]phenol(L) with

general formula [M(L)2(H2O)2] (where M = Cu(II), Co(II) or Ni(II)) have

been synthesized and characterized [151]. All the complexes have octahedral

geometry around central metal ion.