Introduction - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/33782/8/5... · 2018-07-02 · and reactivity are interdependent, studies on molecular structure of transition

1

P. Krishnamoorthy, 2011

Chapter I

Introduction

Coordination and organometallic compounds

Coordination chemistry is undoubtedly the most active research area in inorganic

chemistry that spans the entire spectrum from theoretical works on bonding to the

synthesis of organometallic compounds. Several thousands of coordination complexes

have been synthesized and investigated during the past decades. Research on

coordination chemistry has emerged as an active and interesting field for chemists and

biologists due to the reason that coordination compounds are largely utilized in the

production of fragrances, semiconductors, pharmaceuticals, ceramic precursors etc.1 Ever

since the importance of coordination phenomenon in biological processes was realized,

large number of metal containing macromolecules have been synthesized and studied to

understand the mechanism of complex biological reactions that has resulted in the

emergence of an important branch of inorganic chemistry viz. bioinorganic chemistry.

Similarly, coordination of substrate molecules to metal ions in catalysis was well

understood and lot of research work is being carried out and published. Since structure

and reactivity are interdependent, studies on molecular structure of transition metal

complexes are of paramount importance to understand their properties. Excellent modern

theories available on metal ligand bonding aid the researchers in interpreting the

experimental data obtained using sophisticated instrumental techniques.

Metal complexes have played an important role since the early days of

coordination chemistry. Indeed, a great deal of work has been carried out on the synthesis

and characterization of transition metal compounds mainly due to their applications in

various fields. However, the ability of a metal ion to participate in bonding to all possible

coordination sites depends in part on its preferences for the donor atoms of the ligand, the

flexibility and conformational adaptability of the ligand used, as well as on the

competition from other Lewis acids and different entities capable of occupying the

coordination pocket.

2

Introduction


Medicinal inorganic chemistry is an area of growing interest owing to the fact that

inorganic pharmaceuticals play a key role in clinical therapy. For these inorganic

compounds, the metal serves as structural center for organizing the organic ligands in the

biologically relevant chemical space. Transition metals appear more appealing for this

purpose because they can support a multitude of coordination numbers and geometries

that go far beyond sp, sp2 and sp

3 hybridizations of carbon. Another key aspect for using

metal containing compounds as structural scaffolds is the kinetic stability of the

coordination sphere in the biological environment.

Transition metal complexes act as homogeneous catalysts in many industrially

important reactions such as hydrogenation, hydrosilation, hydroformylation,

polymerisation, isomerisation, acylation and oxidative hydrolysis of olefins. Binuclear

transition metal complexes have also received much attention in recent years as they may

serve as model for variety of biological reactions such as oxygen transport, oxygen

activation, photosynthesis water reduction, electron transfer process, metal-metal

interactions and multi centered catalysis.

Transition metal ions with different oxidations state have a strong role in redox

enzyme systems and may provide the basis of models for active sites. To mention a few,

nickel is an essential component in at least 4 types of enzymes viz. urease, carbon

monoxide dehydrogenase (CODH) or acetyl coenzyme A synthase, hydrogenase and

methyl-S-coenzyme M reductase. Some polydentate Co(II) complexes with ligands

capable of intercalation into DNA strands are capable of inducing DNA cleavage under

photochemical conditions. Since the recognition of Vitamin B12 and synthesis of

cobalmines, responsible for erythrocytes (RBC) formation in human body, there has been

much study of model systems. Copper complexes are known to play important role in the

active site of many copper proteins in vivo as well as in homogeneous and heterogeneous

catalysis for organic chemical reactions. A large body of evidence indicates that copper

chelation is an effective method to inhibit tumor growth and copper chelators have

become promising agents in the treatment of cancer. It has been found that some copper

chelators acquire more effective or novel bioactivity after forming complexes. Recent

3

Introduction


studies indicated that Cu2+

was critically needed for PDTC induced apoptosis in HL-60

cells and the copper complex of salicylaldehyde benzoylhydrazone (SBH) derivatives

showed increased potency of growth inhibition in several cancer cell lines, compared

with the metal-free organics. Copper-SBH complexes were significantly more cytotoxic

than complexes of other transitional metals (Cu > Ni > Zn > Mn > Fe > Cr > Co) in

MOLT-4 cells, an established human T-cell leukaemia cell line. It was noted that SBHs,

especially their copper complexes appeared to be unusually potent inhibitors of DNA

synthesis and cell growth in a variety of human cancer cell lines, including the human

lung epithelial cancer cell line, SKMES-1 and rodent cancer cell lines. A series of, novel

salicylaldehyde pyrazole hydrazone (SPH) derivatives were found capable of inhibiting

the growth of A549 lung carcinoma cells.

Hydrazones

In a brilliant series of investigations in the 1930‟s and the beginning of the

1940‟s, which were reviewed in,2-4

Pfeiffer and his co-workers developed principle

methods for synthesizing azomethine complexes and studied their physicochemical and

structural properties. The first paper describing a metal-containing product of the reaction

of ammonia with salicylaldehyde and cupric acetate appeared in 18405 and in subsequent

years, hundreds of papers on complexes of azomethine were published. Many of these

complexes were included in the review articles6-9

and the subject of azomethine was

represented by 15 papers in the proceedings of the 29th International Conference on

Coordination Chemistry (Lausanne, Switzerland, July1992).10

The architectural beauty of coordination complexes arises from the interesting

ligand systems containing different donor sites. Among the ligand systems, hydrazide and

hydrazone occupy special place because complexes of these compounds with transition

metals are nowadays extensively used for the treatment of several diseases, in synthetic

and analytical chemistry as novel heterogeneous catalysts in oxido-reduction processes

and various chemical and photochemical reactions as well as numerous industrial

applications of science and technology.11-15

4

Introduction


Aroyl hydrazones present a combination of donor sites such as protonated /

deprotonated amide oxygen and the imine nitrogen of hydrazone moiety, very often

additional donor site (usually N or O) is provided by the aldehyde or ketone forming the

Schiff base. Aroyl hydrazones have been proved to be a strong chelating agent for

transition metals,16-21

lanthanides22,23

as well as for main group elements.24,25

They have

also been shown to be useful molecules to build up controllable supramolecular

structures. Lehn and co-workers have demonstrated that suitably substituted hydrazones

are capable of coordinating metals to give multimetallic square grid complexes, whose

optical, photophysical and magnetic properties were modulated by the degree of

protonation of the ligands.26-28

Structure, bonding and stereochemistry of the acid hydrazones

Hydrazones contain two connected nitrogen atoms of different nature and a C=N

bond that is conjugated with a lone electron pair of the terminal nitrogen atom. These

structural fragments are mainly responsible for the physical and chemical properties of

hydrazones (Fig. 1.1). Both the nitrogen atoms of the hydrazone group are nucleophilic,

although the amino type nitrogen is more reactive. The carbon atom of hydrazone group

has both electrophilic and nucleophilic character.29,30

Fig. 1.1 Figure showing the reactivity of hydrazones.

The chelating behavior of hydrazones depends on their amido-iminol tautomerism

and in addition to this, the number and type of the substituents attached to the hydrazone

framework also influences the coordination mode. The functional grouping causes these

compounds to behave as bidentate ligands for metal ions and owing to the availability of

‒ NH‒ C=O group, acid hydrazones show keto-enol (amido-iminol) tautomerism (Fig.

5

Introduction


1.2). In aqueous or ethanolic solutions, these hydrazones show tautomeric structures

which can be coordinated to the metal ion, probably through the N-atom either alone or in

combination with O-atom of the enolic group.31

In solid state, hydrazones predominantly

exist in form (I) (amido), but in solution they exist in form (II) (iminol). In hydrazones, it

is well known that a proton transfer can occur between the hydrazinic-N and keto group

of hydrazide part. Therefore, tautomerisation equilibrium exists between amido form and

iminol form through intramolecular proton transfer. This proton transfer causes a change

in the π-electron configuration and thus increases conjugation.

R2

N

R1

HN

R3

O

R2

N

R1

N

R3

OH

Amido form (I) Iminol form (II)

Fig. 1.2 Tautomerisation of hydrazone ligands.

In general, hydrazones act as a bidentate chelating ligand by utilizing the

available amide oxygen and azomethine nitrogen donor sites by which a five membered

chelate ring is produced and some of the examples are provided in Fig. 1.3.32-34

Uninegative bidentateNeutral bidentate Uninegative bidentate

N

HN

O

M

N

N

O

M

HN

HN

O

M

Fig. 1.3 General bidentate coordination mode of acid hydrazones.

Further, the chelation can be increased by increasing the number of coordination

sites on the hydrazone framework. If a heterocyclic ring or phenolic moiety is attached to

the hydrazone framework as shown in Fig. 1.4, it can coordinate to the metal center with

increased denticity.35-39

6

Introduction


Neutral tridentate

N

HN

O

MN

N

N

O

MN

N

HN

OM O

NN

OM O

Mononegative tridentate Binegative tridentate

Mononegative tridentate

Fig. 1.4 Examples of tridentate behaviour of hydrazone ligands.

It is evident that the stereochemistry of the ligand is much decided by the steric

effects of the various substituents in the hydrazone moiety and most of them are in cis

form while coordinating to the metal ions. This phenomenon is assumed to be due to

better electron delocalisation in the chelate ring system that increases the stability upon

coordination with metal atoms. Hydrazones may also act as a unidentate ligand by

bonding through enolate oxygen when they are existing in a trans form.40

The amido form itself exists in syn or anti conformation depending on the groups

attached with the azomethine bond (Fig. 1.5). In the syn form, as far as the azomethine

bond is concerned two bulkier groups (R2 and R3) are on the same side, while in anti

form the bulkier groups are on opposite side.

R2

N

R1

HN

R3

O

R1

N

R2

N

R3

OH

syn form anti form

Fig. 1.5 Geometrical isomers of hydrazone system.

In addition to the steric effects of the various substituents in the hydrazone

moiety, additional interactions such as intramolecular hydrogen bonding also play a role

7

Introduction


to decide the stereochemistry of hydrazones. It is observed that the syn nature of the bond

usually transforms to anti geometry, while coordinating to metal ions.41,42

Transition metal hydrazone complexes: Applications

The coordination chemistry of hydrazones as ligand is an intensive area of study

and numerous transition metal complexes of them have been investigated.43

Earlier,

investigations on the hydrazone complexes were focused mainly on the synthesis and

structural characterization, but nowadays these metal complexes were reported to serve

some applications in various fields like non-linear optics, sensors, medicine etc.

In bioactivities

Metal complexes containing site-specific substructures and multiple reactive sites

constitute a group of promising candidates for nuclease activity because of their

electronic and structural advantages. Most of the first row transition metals either alone

or in their complex form are biologically essential with a number of known bioactivities.

Among them, nickel, cobalt and copper are especially notable as they involve in many

biological processes.44-53

It is well known that cancer is currently the second leading

cause of death in industrialized countries, accounting for roughly a quarter of total

numbers.54

Hence, development of new anticancer therapies is one of the fundamental

goals in medicinal chemistry. The interactions between biomacromolecules and drugs

have attracted special interest among both chemistry and biology researchers recently.55-

57 DNA is one of the main molecular targets in the design of anticancer compounds

58 and

the interaction between nucleic acids and other molecules is a fundamental issue in life

science that relates the replication, transcription, mutation of genes and related variations

of species in character, origin of some diseases and mechanism of interaction of some

DNA-targeted drugs.59-62

Further, it has been demonstrated that free radicals can damage

proteins, lipids and DNA of bio-tissues leading to increased rates of cancer and

fortunately antioxidants can prevent this damage due to their free radical scavenging

activity.63,64

Hence, it is very important to develop compounds with strong DNA binding,

antioxidant and cytotoxic properties for effective cancer therapy. As known well, serum

albumins are the class of proteins involved in the transport of metal ions and metal

8

Introduction


complexes along with drugs through the blood stream.65

Many drugs, including

anticoagulants, tranquilizers, antiinflammatory and general anaesthetics are transported in

the blood via combination with albumin.66,67

The nature and magnitude of drug-albumin

interaction significantly influence the pharmacokinetics of drugs and thus the binding

parameters are useful in studying protein-drug binding as they greatly influence

absorption, distribution, metabolism and excretion properties of typical drugs.

In molecular sensors

Recently, the development of molecular sensors has attracted lot of research

activities for their use in processes that include food, clinical, environmental analysis and

analytical applications. It was reported that a potentiometric aluminium sensor based on

N,N'-bis(salicylidene)-1,2-cyclohexanediamine as a neutral carrier in poly(vinyl chloride)

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

industrial and environmental samples 68

in the pH range of 2.0-9.0. It has been used as an

indicator electrode in potentiometric titration of aluminium ion with EDTA. The Schiff

base, N,N′,N″,N′′′-1,5,8,12-tetraazadodecane-bis(salicylaldiminato), has been used as an

ionophore for preparing Mn2+

selective sensor69

over a number of alkali, alkaline and

heavy metal ions for the determination of manganese in various samples by direct

potentiometry.

In non-linear optical devices

Non-linear optics (NLO) deals with the interactions of applied electromagnetic

fields materials to generate new electromagnetic fields, altered in frequency, phase, or

other physical properties. Such materials that are able to manipulate photonic signals

efficiently are of importance in optical communication, optical computing and dynamic

image processing.70-74

In this connection, transition metal complexes have emerged as

potential building blocks for nonlinear optical materials due to various excited states

present in these systems as well as their ability to tailor metal-ligand interactions.75-80

Compared to the more common organic molecules, metal complexes offer a large variety

of novel structures, the possibility of enhanced thermal stability and a diversity of tunable

electronic behaviours by virtue of the coordinated metal center and hence they may find

9

Introduction


use as NLO materials with unique magnetic and electrochemical properties.81-83

Investigations on NLO properties of metal complexes are being pursued by several

research groups.84-90

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

Schiff base complexes exhibit good second order NLO properties.91-97

Based on the above facts, studies on the chelating properties of hydrazone ligands

and the effect of coordination of them on the composition and geometry of the complexes

containing cobalt(II), nickel(II) and copper(I/II) ions were undertaken as the subject of

the present work. Additionally, comparison on the biological properties of hydrazone

complexes with respect to DNA / BSA interactions, free radical scavenging and

cytotoxicity under in vitro conditions have been carried out.

Survey of the previous work

Though voluminous reports are available in the literature on the chemistry and

other aspects of metal hydrazone complexes, some of them relevant to our work alone

were reviewed and presented in this part of the Introduction chapter.

Yi-Heng Lu et al.98 reported the synthesis and characterization of Co(II)

complexes containing salicyladehyde benzoylhydrazone (SBH) and established that the

ligand has three sites suitable for coordination bond formation. The UV-visible

absorption spectra using deconvolution method showed that the structure of complex in

solution is different from that in solid crystals. The nature of complexes in solution

depends on acidity of the phenolic proton of SBH and on the medium. In neutral or

slightly acidic medium, the SBH is a non-charged bidentate ligand and the free hydroxyl

group on the SBH molecule makes it possible to form hydrogen bonds in solution. In

basic medium, the SBH is a uninegatively charged tridentate ligand.

N

HN

OO Co

OAc

10

Introduction


Recently, the first Co(III)/Co(III) ionic complex with hydrazone and azide

ligands, [Co(L)2]+[Co(L)(N3)3]

-·CH3OH was structurally and electrochemically

characterized by Bikasa et al.99 in which HL = N'-[(1E)-1-pyridin-2-ylethylidene]-2-

furohydrazide was used as a ligand. In the cation [Co(L)2]+, two units of furanhydrazone,

each of them with three donor atoms constitute a meridional arrangement around the

cobalt atom. The coordination polyhedron is a CoO2N4 distorted octahedron for the

cation and a CoON5 distorted octahedron for the anion. Cyclic voltammetric experiments

of the [Co(L)2]+[Co(L)(N3)3]

- in DMSO revealed the reduction of ligand at -1.56 V and

two reduction potentials at -0.81 and -1.28 V respectively, for two different Co(III) ions.

N

CH3

NN

O

O

CoN

CH3

NN

O

O

N

CH3

NN

O

O

Co

N

N

N

N

N

N

N3

+ -

A novel ligand 2-acetyl-2-thiazoline acetylhydrazone (ATHAc) and two new

chloride-bridged dimeric nickel(II) complexes containing thiazoline hydrazone derivative

ligands, [{Ni(ATsc)(MeOH)}2(μ-Cl)2]Cl2 (1) (ATsc = 2-acetyl-2-thiazoline

semicarbazone) and [{Ni(ATHAc)(H2O)}2(μ-Cl)2]Cl2 (2) were prepared and structurally

characterized using elemental analysis, single crystal X-ray diffraction, IR and UV-

SN

H3CN

N

R

O

Ni

O HH

SN

CH3

N

N

R

O

Ni

OHH

Cl

Cl

2

visible spectroscopy by Vinuelas-Zahinos et al.100 The coordination geometry around

each nickel ion was described as a distorted octahedron coordinated to one thiazoline

11

Introduction


nitrogen atom, one imine nitrogen atom, one carbonyl oxygen atom, one oxygen atom

(from a methanol molecule in 1 and from a water molecule in 2) and two bridging

chloride ligands.

From the reaction between Cu(II) and Ni(II) salts and the Schiff base 6-amino-5-

formyl-1,3-dimethyluracil-benzoylhydrazone (H2BEZDO), in dimethylformamide

(DMF)-water and ammonia media, the complexes [Ni(BEZDO)]·H2O·NH3 (1),

[Cu(BEZDO)]·H2O·NH3 (2) and [Cu(BEZDO)(H2O)]·H2O (3) containing the dianionic

organic ligand have been obtained. These compounds have been studied by IR, electronic

and EPR spectroscopy and magnetic measurements. The structure of

[Cu(BEZDO)(H2O)]H2O has been solved by means of X-ray diffraction method. The

coordination environment around the Cu(II) was a square-plane structure in which the

Schiff base acts as tridentate ligand through the N(6), N(51) and O(52) atoms, making

both a five and six membered chelate rings. The coordination sphere is completed with

the oxygen atom of a water molecule.101

NN

ONH

Cu

OHH

O

O

H3C

CH3

3

Galic et al.102

reported the solution and solid-state complexation behaviour of first

series transition metal cations, Cd(II) and Al(III) with two aroylhydrazones derived from

nicotinic acid hydrazide and salicylaldehyde or o-vanillin at 25 °C in buffered dioxane /

water 1 / 1 mixture (pH, 5.8) by means of spectrophotometric and spectrofluorimetric

titrations. The addition of Mn(II) or Cd(II) ions to hydrazone solutions had no effect on

their absorption spectra whereas the addition of Ni(II) and Cr(III) immediately caused

precipitation.

12

Introduction


NN

OO

N

M

R

NN

OO

N

M

R

where, M = Cu(II) (or) Ni(II) (or) Zn(II); R = H (or) CH3

Three new diorganotin(IV) complexes of the general formula R2Sn[3-(OMe)-2-

OC6H3CH=N–N=C(O)Ph] (R = Ph, Ia; R = Me, Ib; R = n-Bu, Ic) have been synthesised

from the corresponding diorganotin(IV) dichlorides and the ligand, N'-(2-hydroxy-3-

methoxybenzylidene)benzohydrazide in methanol at room temperature in the presence of

trimethylamine.103

All the complexes have been characterized by elemental analysis, IR

and 1H,

13C,

15N,

119Sn NMR spectra and their structures have been confirmed by single

crystal X-ray diffraction analysis of the representative compound Ia in which the ligand

N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide (H2L) coordinates to the metal

centre in the enolate form via the phenolic O, imino N and enolic O atoms. In the

complex Ia, the central tin atom adopted a distorted trigonal bipyramidal coordination

geometry with the oxygen atoms in axial positions, while the imino nitrogen atom of the

Schiff base and the two phenyl groups occupy the equatorial sites.

O

NN

OSn

R ROCH3

where, R = CH3 (or) CH3CH2CH2CH3 (or) C6H5

A new aroyl hydrazone, N-2-hydroxy-4-methoxybenzaldehyde-N-4-nitrobenzoyl

hydrazone [H2L], its binuclear [Cu2L2] (1) and mixed ligand copper(II) mononuclear

complexes [CuLpy] (2) [py = pyridine] have been prepared by Raj et al.104 The structures

determined by single crystal X-ray diffraction showed that the ligand molecule exits in

13

Introduction


the keto form in the solid state, while at the time of complexation, it tautomerises into the

ligand molecule i.e., both the phenolic and the enolic protons.

NN

OO Cu

NO2

H3CO

NN

OO

O2N

OCH3Cu

NN

OO Cu

NO2

H3CO

N

21

“Tritopic” picolinic dihydrazone ligands with tridentate coordination pockets

were designed to produce homoleptic [3×3] nonanuclear square grid complexes on

reaction with transition metal salts and many structurally documented examples have

been obtained with Mn(II), Cu(II) and Zn(II) ions. However, other oligomeric complexes

with smaller nuclearities have also been identified structurally in some reactions

involving Fe(II), Co(II), Ni(II) and Cu(II) with certain tritopic ligands. This illustrates the

dynamic nature of the metal-ligand interaction and the conformationally flexible nature

of the ligands and points to the possible involvement of some of these species as

intermediates in the [3×3] grid formation process. Examples of mononuclear, dinuclear,

hexanuclear, heptanuclear and nonanuclear species involving Fe(II), Co(II), Ni(II) and

Cu(II) salts with a series of potentially heptadentate picolinic dihydrazone ligands with

pyrazine, pyrimidine and pyridine end groups were described in the same study.105

Cobalt(III) complexes of diacetyl monooxime benzoyl hydrazone (dmoBH2) and

diacetyl monooxime isonicotinoyl hydrazone (dmoInH2) have been synthesized and

characterized by elemental analyses and spectroscopic methods by Naskar et al.106 The

X-ray crystal structure of the hydrazone ligands, as well as that of the cobalt(III) complex

[CoIII

(dmoInH)2]Cl·2H2O (1) were also reported in which the amide and the oxime

hydrogens are deprotonated for both the ligands, while the isonicotine nitrogens are

14

Introduction


protonated. In the [CoIII

(dmoBH)2]Cl (2) complex, only the amide nitrogens are

deprotonated. It was shown that the additional hydrogen bonding capability of the

H3CN

N

NO

N+

CoH3C

O-

N+

NO

NCH3

CH3N

-O

Cl-

1

H H

isonicotine nitrogen resulted in different conformation and supramolecular structure for

dmoInH2, compared to dmoBH2, in the solid state. Comparing the structure of the

[CoIII

(dmoInH)2]Cl·2H2O with that of the Zn(II) complex of the same ligand reported

earlier, it is seen that the metal ion has a profound influence on the supramolecular

structure due to change in geometrical dispositions of the chelate rings.

Synthesis, structural investigation by elemental analyses, magnetic susceptibility

measurements, electronic, IR, NMR and EPR spectral techniques and corrosion inhibition

studies on cobalt(II), nickel(II), copper(II) and zinc(II) complexes with 2-acetylthiophene

benzoylhydrazone (Hatbh) was investigated by Singh et al.107 The molecular structures of

ligand and its copper(II) complex have been determined by single crystal X-ray

diffraction technique. The Cu(II) complex possesses a CuN2O2 chromophore with a

considerable delocalization of charge. The structure of the complex was stabilized by

intermolecular – stacking and C–H··· interactions. Hatbh acts as a monobasic

bidentate ligand in all the complexes bonding through a deprotonated C–O- and C=N

groups. Electronic spectral studies indicated an octahedral geometry for the Ni(II)

complex while square planar geometry for the Co(II) and Cu(II) complexes. EPR

spectrum of the Cu(II) complex exhibits a square planar geometry in both solid and in

DMSO solution. The trend g|| > g > 2.0023 indicates the presence of an unpaired electron

15

Introduction


in the dx2

-y2 orbital of Cu(II). The electrochemical study of Cu(II) complex revealed a

metal based reversible redox behavior.

CH3

NN

O

S

Cu

H3C

NN

O

S

A new series of macrocyclic unsymmetrical binuclear copper(II) [CuLa,b

]

complexes was prepared by Sengottuvelan et al.108 using 6,6′-piperazine-1,4-

diyldimethylenebis(4-methyl-2-formyl)phenol (La) and 6,6′-piperazine-1,4-

diyldimethylenebis(4-bromo-2-formyl)phenol (Lb) and [Cu(oxen)](ClO4)2 or

[Cu(oxpn)](ClO4)2 (where oxen = N,N′-bis(2-aminoethyl)oxamide and oxpn = N,N′-bis(3-

aminopropyl)oxamide). The binuclear copper(II) complexes contain three different

compartments: the first compartment has two piperazinyl nitrogens and two phenolic

oxygens (N2O2), the second compartment has two phenolic oxygens and two imine

nitrogens (O2N2) and the third compartment has two imine nitrogens and two amide

nitrogens (N4) as coordinating sites. Apart from the three compartments, the complex has

two oxamide oxygen atoms for further coordination. The copper(II) ion in the complex is

2+

where, L1a: R = (CH2)2, X = CH3; L1b: R = (CH2)2, X = Br;

L2a: R = (CH2)3, X = CH3; L2b: R = (CH2)3, X = Br

ON N

O NNCu

OHN

NH

O

(R)

(R)

Cu

X

X

(ClO4-)2

16

Introduction


tetracoordinated with two tertiary nitrogen atoms and two phenoxy oxygen atoms

coordinated in the equatorial plane to the copper(II) ion and the geometry around the

copper nuclei is distorted square planar. Both mono and binuclear copper(II) complexes

were characterized by elemental, electronic, EPR, etc., Further, the electrochemical

studies of the mono- and binuclear copper(II) complexes were also are discussed.

Dioxo- and oxovanadium(V) complexes of biomimetic, ONO and NNS donor

hydrazone ligands and their catalytic reactivity was reported by Monfared et al.109

Oxo-

and dioxovanadium(V) complexes of hydrazone ONO donor ligands with the formula

[VVO(μ2-OCH3)(L

1)]2 (1) and [V

VO2(L

2)]·H2O (2) were synthesized by the reaction of

[VO(acac)2] with proton transfer complexes of benzenetricarboxylic acid /

benzoylhydrazide and benzenetricarboxylic acid / isonicotinohydrazide, respectively

(H2L1 = monocondensation of benzoylhydrazide and acetylacetone, H2L

2 =

monocondensation of isonicotinohydrazide and acetylacetone). Dioxo complex of V(V),

[VO2(L3)] (3), was synthesized by the reaction of equimolar amounts of VO(acac)2, 2-

acetylpyridine and thiosemicarbazide (H2L3 = hydrazone Schiff base of acetylpyridine

and thiosemicarbazide and Hacac = acetylacetone) and characterized by FT-IR, UV-

visible and NMR spectroscopic methods. The crystal structures of 1 and 2 were

determined by X-ray analyses. The 1H NMR spectrum of the complex 1 in CDCl3

solution indicated that this dimeric complex is converted appreciably into its respective

monomeric form. The catalytic potential of the complexes has been tested for the

oxidation of alkene, alkane and aromatic hydrocarbons using H2O2 as the terminal

oxidant.

H3C

NN

OO

CH3

V

O

OCH3

CH3

NN

OO

H3C

V

O

H3COH3C

NN

OO

NH+CH3

V

OO

1

3

17

Introduction


New macrocyclic binuclear nickel(II) complexes have been synthesized by using

the bicompartmental mononuclear complex [NiL] [3,3′-((1E,7E)-3,6-dioxa-2, 7-

diazaocta-1,7-diene-1,8-diyl)bis(3-formyl-5-methyl-2-diolato)nickel(II)] with various

diamines like 1,2-bis(aminooxy)ethane (L1), 1,2-diamino ethane (L

2), 1,3-diamino

propane (L3), 1,4-diamino butane (L

4), 1,2-diamino benzene (L

5) and 1,8-diamino

naphthalene (L6). The complexes were characterized by elemental analysis and

spectroscopic methods. The molecular structures of the symmetrical binuclear complex

[Ni2L1(H2O)4](ClO4)2 (1) and unsymmetrical binuclear complex [Ni2L

3(H2O)4](ClO

4)2·(H2O)4 (3) were determined by single-crystal X-ray diffraction which reveled that

geometry around both the nickel(II) ions in each molecule is a slightly distorted

octahedral. The influence of the coordination geometry and the ring size of the

binucleating ligands on the electronic, redox, phosphate hydrolysis, DNA binding and

cleavage properties have been studied.110

A novel difunctional acylhydrazone has been synthesized by the reaction of 5-

methylisoxazole-4-carboyl hydrazine with benzaldehyde and characterized by X-ray

crystallography and spectroscopy by Jin et al.111 Moreover, the spectroscopic properties

were evaluated through density functional theory (DFT) and time-dependent density

functional theory (TD DFT) calculations. In addition, the results of antibacterial activities

indicated that the title compound has certain modest antibacterial activity as well as the

broad-spectrum bacteriostasis, which can be supported by the molecular electrostatic

potential (MEP). Therefore, it is concluded that the title compound possess both

antibacterial activity and photoluminescent property, which has potential applications in

many fields such as material science and photodynamic therapy.

N NH

O

N

O

H3C

A new bis-phenanthroline dicopper(II) complex has been synthesized and

characterized by elemental analysis and spectroscopic methods by Anbu et al.112

The

molecular structure of the dinuclear Cu(II) complex [Cu2(μ-CH3COO)(μ-H2O)(μ-

18

Introduction


OH)(phen)2]2+

(phen = 1,10-phenanthroline) (1) was determined by single crystal X-ray

diffraction technique. The coordination environment around each Cu(II) ion in complex 1

was described as slightly distorted square pyramidal geometry. The electronic, redox,

phosphate hydrolysis, DNA binding and DNA cleavage have been studied. The

antiproliferative effect of complex 1 was confirmed by the lactate dehydrogenase (LDH)

enzyme level in MCF-7 cancer cell lysate and content media. The dicopper(II) complex

inhibited the LDH enzyme as well as the growth of the human breast cancer MCF7 cell

line in minimum concentration level.

A series of mono and binuclear copper(II) complexes, of general formulae

[CuL](ClO4) and [Cu2L](ClO4)2, respectively, have been synthesized from lateral

macrocyclic ligands that have different compartments, originated from their

corresponding precursor compounds 3,4:9,10-dibenzo-1,12-[N,N′-bis{(3-formyl-2-

hydroxy-5-methyl)-benzyl}diaza]-5,8-dioxacyclotetradecane (PC-1) and

3,4:9,10-dibenzo-1,12-[N,N′-bis{(3-formyl-2-hydroxy-5-methyl)-benzyl}diaza]-5,8-

dioxacyclopentadecane) (PC-2). The structure of the precursor compound PC-1,

O N O

CH3

N

O N O N

CH3

Cu(CH2)m (CH2)nCu

ClO4

+

where, L1a: m = 2, n = 2; L1b: m = 2, n = 3; L1c: m = 2, n = 4;

L2a: m = 3, n = 2; L2b: m = 3, n = 3; L2c: m = 3, n = 4

(ClO4-)2

mononuclear copper(II) complex [CuL1a

](ClO4) and binuclear copper(II) complex

[Cu2L2c

](ClO4)2 were determined using single crystal XRD. In addition, electrochemical,

magnetic moment and EPR studies evidenced the mono and binuclear nature of them.

19

Introduction


The observed initial rate constant values of catechol oxidation, using complexes as

catalysts, range from 4.89×10-3

to 5.32×10-2

min-1

and were higher for binuclear

complexes than for the corresponding mononuclear complexes.113

Five new copper(I) complexes containing PPh3 and [2,3]-pyrazino-[1,10]

phenanthroline-2,3-dicarbonitrile (C16H6N6) [Cu(PPh3)(C16H6N6)Cl]·H2O (1),

[Cu(PPh3)(C16H6N6)Br]·CH3CN (2), [Cu(PPh3)(C16H6N6)I]·CH3CN (3),

[Cu(PPh3)(C16H6N6)(CN)]·0.5 CH2Cl2 (4) and Cu(PPh3)(C16H6N6)(SCN) (5) have been

synthesized for the first time114

by the reactions of CuX (X = Cl, Br, I, CN, SCN) with

the bidentate ligand C16H6N6 and the monodentate ligand PPh3 in the molar ratio of 1:1:1

in the mixed solvent of CH2Cl2 and CH3CN (5 mL / 5 mL). They are characterized by X-

ray crystallography, luminescence, IR, 1H NMR and

31P NMR. All the complexes exhibit

intense luminescence in solid state at room temperature.

The macrocyclic symmetrical and a series of unsymmetrical binuclear copper(II)

complexes have been synthesized by using mononuclear complex [CuL] [3,30-((1E,7E)-

3,6-dioxa-2,7-diazaocta-1,7-diene-1,8- diyl)bis(3-formyl-5-methyl-2-diolato)copper(II)].

Another compartment of the [CuL] have been condensed with various diamines like 1,2-

bis(aminooxy)ethane (L1), 1,2-diamino ethane (L

2a), 1,3-diamino propane (L

2b), 1,4-

diamino butane (L2c

), 1,2-diamino benzene (L2d

), 1,8-diamino naphthalene (L2e

) and

characterized by elemental analysis, spectroscopic and X-ray crystallographic methods.

The influence of the coordination geometry and the ring size of the binucleating ligands

on the electronic, redox, magnetic, catecholase activity, DNA binding and cleavage

properties have been studied. The molecular structures of the symmetrical binuclear

complex [Cu2L1(H2O)2](ClO4)2 (1) and unsymmetrical binuclear complex

[Cu2L2b

(ClO4)(H2O)]ClO4 (2b) were determined by X-ray crystallography. The aromatic

diamine condensed macrocyclic ligands of copper(II) complexes display better DNA

interaction and significant chemical nuclease activity than the aliphatic diamine

condensed macrocyclic Cu(II) complexes115

.

20

Introduction


Two types of copper(II) and nickel(II) complexes derived from benzophenone

anthranoylhydrazone (L1), 2-acetonaftanone anthranoylhydrazone (L2), 4-

phenylacetonaftonone anthranoylhydrazone (L3), benzophenone salicyloylhydrazone

(L4), 2-acetonaftanon salicyloylhydrazone (L5), 4-phenylacetonaftanon

salicyloylhydrazone (L6) and bidentate heterocyclic base [1,10-phenanthroline (phen)]

with general stoichiometry [M(L)2] and [ML(phen)]Cl have been synthesized and

characterized by Gup et al.116

Cytotoxicity, quantitative structure-activity relationships of salicylaldehyde

benzoylhydrazone analogs and their transition metal complexes have been discussed by

Ainscough et al.117 For this discussion, a series of salicylaldehyde benzoylhydrazone

derivatives, their copper(II) complexes and a range of transition metal complexes of the

unsubstituted ligand have been synthesized and evaluated for cytotoxicity against a

human adenocarcinoma cell line. The QSAR analysis revealed a strong correlation

between the ligand cytotoxicity with electronic and transport factors that can be modeled

by treating each „half‟ of the molecule as an isolated unit. Activity increases when

substituents in the benzoyl ring were electron withdrawing whereas for the

salicylaldehyde ring electron donation was required. However, the activity of the

transition metal complexes of the unsubstituted ligand mirrored charge density on the

metal.

O

N

HN

OCu

Cl

R1

R2

The key role of hydrogen bonding in the nuclearity of three copper(II) complexes

with hydrazone derived ligands and nitrogen donor heterocycles were reported by Shit et

al.118 Three new Cu(II) complexes of formula [Cu(L

1)(pyz)(CH3OH)]ClO4 (1),

[Cu(L1)(4,4'-bpy)(ClO4)]·0.5H2O (2) and [{Cu(L

2)(ClO4)}2(μ-4,4'-bpy)] (3) have been

synthesised by using pyrazine (pyz) and 4,4'-bipyridine(4,4'-bpy) and tridentate O,N,O-

donor hydrazone ligands, L1H and L

2H, obtained by the condensation of 1,1,1-trifluoro-

21

Introduction


2,4-pentanedione with salicyloylhydrazide and benzhydrazide, respectively. The ligands

and their complexes have been characterized by elemental analyses, FT-IR and UV-

visible spectroscopies. Single crystal X-ray structure analysis revealed the metal ion in a

slightly distorted square pyramidal geometry in all the complexes. However, complexes 1

and 2 are mononuclear with pyz and 4,4'-bpy, respectively showing an unusual

monodentate behavior while complex 3 is dinuclear with 4,4'-bpy adopting the typical

bridging coordination mode.

O

HNN

H3C

O

F

FF

Cu

NO4Cl

N

3

O

NHN

CH3

OF

F

F

Cu

ClO4

OH

O

NHN

CH3

O

F

FF

Cu

N

N

OH CH3

ClO4-

OH

O

NHN

CH3

O

F

FF

Cu

N

OH CH3

ClO4-

N

12

Wang et al.119 reported the synthesis, characterisation and calf-thymus DNA

interaction studies of neutral mononuclear Ln(III) complexes with 7-methoxychrom-one-

3-carbaldehyde-isonicotinoyl hydrazone ligand. The antioxidant activities of the ligand

and its Ln(III) complexes were also investigated.

Schleife et al.120 investigated the metal complexation properties of a

functionalized N3O2 donor ligand H2L2, where H2L2 stands for 2,6-diacetyl-4-

22

Introduction


carboxymethyl-pyridine bis(benzoylhydrazone). The ligand H2L2 is observed to react

essentially in the same fashion as its unmodified parent H2L1 producing mixed-ligand

[M(H2L2)(Cl2)] complexes (M = MnII (1), Co

II (3)) upon treatment with MCl2.

Complexes [M(HL2)(H2O) (EtOH)]BPh4; (M = MnII (2), M = Co

II (4)), incorporating the

supporting ligand in the partially deprotonated form (HL2)-, are formed by salt

elimination of the [M(H2L2)(Cl2)] compounds with NaBPh4. Compounds 2 and 4 are

isostructural featuring distorted pentagonal-bipyramidal coordinated MnII and Co

II ions,

with the H2O and EtOH ligands bound in axial positions.

HN

O

N

H3CN

CH3

NNH

O

O O-

M

Cl Cl

HN

O

N

H3CN

CH3

NN

O

O O-

M

OH2EtOH

where, M = Mn(II) (or) Co(II)

(BPh4)-+

1 (or) 3 2 (or) 4

The reactions between bis(acetylacetonato)dioxomolybdenum(VI) and Schiff base

ligands derived from 5-chlorosalicylaldehyde or 3-ethoxy-salicylaldehye and 3-methoxy-

benzoic hydrazide (m-anisic hydrazide), 2-furoic hydrazide or 2,4-dihydroxy-benzoic

hydrazide in the presence of donor solvents yielded cis-dioxomolybdenum(VI)

complexes with the general formula MoO2L(D), where L = tridentate Schiff base ligand

and D = dimethylsulfoxide, hexamethylphosphoramide, dimethylformamide, imidazole

or methanol. The complexes were characterized by elemental analysis, electronic spectra,

IR, 1H and

13C NMR spectroscopies, thermogravimetric analysis, cyclic voltammetry and

the molecular structures of five of the dioxomolybdenum complexes were elucidated by

single crystal X-ray diffraction studies.121

In general, the complexes adopt an octahedral

environment around the Mo center with a cis-oxo configuration. The other coordination

sites are occupied by the imino nitrogen, phenoxyl oxygen, hydroxyl oxygen of the

tridentate Schiff base and the donor atom of the solvent molecule. The structural data

23

Introduction


revealed that the labile coordination site, which is occupied by N or O atoms from the

donor solvents, has a longer Mo–O or Mo–N bond distance.

NN

O

Cl

O Mo

O OO

P N(CH3)3

(H3C)3N N(CH3)3

ONN R

O

Cl

O Mo

O OO

S

H3C

CH3

where, R = 3-(CH3O)C6H4 (1) (or) 2-(C4H3O) (2)

(or) 2,4-(OH)2C6H3) (3)

NN

OO Mo

O ODOC2H5

OCH3

where, D = HMPA (5) (or) DMSO (6) (or) DMF (7) (or) Imz (8) (or) MeOH (9)

4

Two new copper(II) complexes have been synthesized by reacting 2-oxo-1,2-

dihydroquinoline-3-carbaldehyde-(benzoyl)-hydrazone (H2L) with CuCl2·2H2O or

Cu(NO3)2·3H2O.122

The structure of the complexes have been determined by single

crystal X-ray diffraction studies. Results obtained using spectroscopic methods strongly

suggested that the ligand and its Cu(II) complexes interacted with calf thymus DNA

through intercalation. In the case of protein binding, the obtained results indicated that all

the three compounds could quench the intrinsic fluorescence of bovine serum albumin

through static quenching process. In addition, antioxidant activity tests showed that H2L

and its copper(II) complexes possess significant scavenging effect against free radicals.

Further, the two copper(II) complexes exhibited effective cytotoxic activity against a

panel of human cancer cell lines.

Six new copper complexes of di-2-pyridyl ketone nicotinoylhydrazone and their

versatile binding properties (HDKN) have been studied by Mangalam et al.123 The

24

Introduction


complexes have been characterized by a variety of spectroscopic techniques and the

structure of [Cu(DKN)2]·H2O (1) determined by single crystal X-ray diffraction was

proved to be distorted octahedral geometry. The EPR spectra of compounds

[Cu2(DKN)2(μ-N3)2] (2) and [Cu2(DKN)2(μ-NCS)2] (3) in polycrystalline state suggested

a dimeric structure as they exhibited a half field signal, which indicate the presence of a

weak interaction between two Cu(II) ions in these complexes.

NN

O

N

Cu

NN

O

N

1

A new series of stable transition metal complexes of the formula [M(L)X·S] (

where M = Cu(II), Ni(II), Co(III), Cr(III) and Fe(III) and L is the deprotonated ligand of

4-hydroxy-coumarin-3-thiocarbohydrazone, X = Cl-, NO3

- or CH3COO

- and S = H2O and

/ or EtOH) have been prepared.124

The ligand HL acts as a monobasic tridentate ONS

donor in all metal complexes and coordinated through the phenolic OH, azomethine

nitrogen and thione sulfur. The formed complexes after releasing the solvent were

investigated and their structures are suggested to have square planar or octahedral

arrangement. Pharmacodynamic of cobalt(III) complex on some biochemical parameters

and histological studies in serum and heart tissue in rats have been studied. Although the

complexes demonstrated a significant effect at low dose than the high dose, the ligand

showed significant good effects in both high and low doses on the biochemical analysis

in serum and heart tissue. Cobalt complex was screened in order to evaluate its antifungal

activity against the filamentous fungi Aspergillus niger, Aspergillus fumigatus and

Aspergillus flavus and antibacterial activity against the Candida albicans, Escherichia

coli, Klebseilla pneumoniae and Pseudomonas aeruginosa.

25

Introduction


The coordination behavior of a new dihydrazone ligand, 2,6-bis[(3-

methoxysalicylidene) hydrazinocarbonyl]pyridine towards manganese(II), cobalt(II),

nickel(II), copper(II), zinc(II) and cadmium(II) has been described by Vadavia et al.125

The metal complexes were characterized by magnetic moments, conductivity

measurements, spectral (IR, NMR, UV-visible, FAB mass and EPR) and thermal studies.

IR spectral studies revealed the nonadentate behavior of the ligand. The X-band EPR

spectra of copper(II) complex at both room temperature and liquid nitrogen temperature

showed unresolved broad signals with giso = 2.106. Cyclic voltammetric studies of

copper(II) complex at different scan rates revealed that all the electrochemical reactions

are irreversible in nature.

O

H3CO

NN

ON

N

O

N

OCH3

OM

Cl ClH2O

MM

OH2 OH2

OH2

H2OH2O

H2O

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

Six copper(II) complexes of 2-hydroxy-4-methoxybenzaldehyde

nicotinoylhydrazone (H2hmbn), 2-hydroxy-4-methoxyacetophenone nicotinoylhydrazone

(H2hman), 2-hydroxy-4-methoxybenzaldehyde benzoylhydrazone (H2hmbb) and 2-

hydroxy-4-methoxyacetophenone benzoylhydrazone (H2hmab) have been synthesized by

Mathew et al.126

The complexes viz. [Cu(hmbn)]2·2H2O (1), [Cu(hman)]2 (2),

[Cu(hmbb)]2·2H2O (3), [Cu(hmbb)phen]·1(1/2)H2O (4), [Cu(hmbb)(bipy)·H2O] (5) and

[Cu(hmab)phen] (6) were characterized by different physicochemical techniques. The

crystal structure of complex 6 showed that it possesses a distorted square pyramidal

geometry with π–π stacking interactions and significant C–H···π interactions.

26

Introduction


CH3

NN

O

H3CO

O

CuN

N

6

A number of indolo[3,2-c]quinolines were synthesized and modified at the lactam

unit to provide a peripheral binding site to accommodate metal ions.127

Potentially

tridentate ligands HL1a

-HL4a

and HL1b

-HL4b

were reacted with copper(II) chloride in

isopropanol/methanol to afford novel five-coordinate copper(II) complexes

[Cu(HL1a-4a

)Cl2] and [Cu(HL1b-4b

)Cl2]. In addition, a new complex [Cu(HL5b

)Cl2] and

two previously reported compounds [Cu(HL6a

)Cl2] and [Cu(HL6b

)Cl2] with modified

paullone ligands HL5b

, HL6a

and HL6b

which can be regarded as close analogues of

indoloquinolines HL1b

, HL4a

and HL4b

in which the pyridine ring was formally

substituted by a seven-membered azepine ring, were synthesized and compared. The new

ligands and copper(II) complexes were characterized by 1H and

13C NMR, IR and

electronic absorption spectroscopy, ESI mass spectrometry, magnetic susceptibility

measurements in solution at 298 K ([Cu(HL1a

)Cl2] and [Cu(HL4b

)Cl2]) and X-ray

crystallography ([Cu(HL3b

)Cl2]·3DMF, [Cu(HL4b

)Cl2]·2.4DMF, HL5b

and

[Cu(HL5b

)Cl2]·0.5CH3OH). All complexes were tested for cytotoxicity in the human

cancer cell lines CH1 (ovarian carcinoma), A549 (non-small cell lung cancer) and

SW480 (colon carcinoma). The compounds are highly cytotoxic, with IC50 values

ranging from nanomolar to very low micromolar concentrations. Substitution of the

seven-membered azepine ring in paullones by a pyridine ring resulted in a six to nine fold

increase of cytotoxicity in SW480 cells. Electron-releasing or electron-withdrawing

substituents in position 8 of the indoloquinoline backbone do not exert any effect on

cytotoxicity of copper(II) complexes, whereas copper(II) compounds with Schiff bases

obtained from 2-acetylpyridine and indoloquinoline hydrazines are 10 to 50 times more

27

Introduction


cytotoxic than those with ligands prepared from 2-formylpyridine and indoloquinoline

hydrazines.

Complexes of Co(II), Ni(II), Cu(II), Mn(II), Cd(II), Zn(II), Hg(II) and U(IV)O2

with N′-(1-(4-hydroxyphenyl)-ethylidene)-2-oxo-2-(phenylamino)acetohydrazide

H3OPAH) are reported and have been characterized by various spectroscopic techniques

like IR, UV-visible, 1H NMR and EPR as well as magnetic and thermal (TG and DTA)

measurements.128

It was found that the ligand behaves as a neutral bidentate,

monoanionic tridentate or tetradentate and dianionic tetradentate. An octahedral

geometry for [Mn(H3OPAH)2Cl2], [Co2(H2OPAH)2Cl2(H2O)4] and

[(UO2)2(HOPAH)(OAc)2(H2O)2] complexes, a square planar geometry for

[Cu2(H2OPAH)Cl3(H2O)]·H2O complex, a tetrahedral structure for [Cd(H3OPAH)Cl2],

[Zn(H3OPAH)(OAc)2] and [Hg(H3OPAH)Cl2]H2O complexes. The binuclear

[Ni2(HOPAH)Cl2(H2O)2]·H2O complex contains a mixed geometry of both tetrahedral

and square planar structures.

The design of novel Fe chelators with high Fe mobilization efficacy and low

toxicity remains an important priority for the treatment of Fe overload disease. Some

new methyl pyrazinylketone isonicotinoyl hydrazone (HMPIH) analogs were designed

and synthesised based on previously investigated aroylhydrazone chelators. The HMPIH

series demonstrated high Fe mobilization efficacy from cells and showed limited to

moderate antiproliferative activity. Importantly, this novel series demonstrated

irreversible electrochemistry which was attributed to the electron-withdrawing effects of

the non-coordinated pyrazine N-atom. The latter functionality played a major role in

forming redox-inactive complexes that prevent reactive oxygen species generation. In

fact, the Fe complexes of the HMPIH series prevented the oxidation of ascorbate and

hydroxylation of benzoate. It was determined that the incorporation of electron-

withdrawing groups is an important feature in the design of N,N,O-aroylhydrazones as

candidate drugs for the treatment of Fe overload disease.129

28

Introduction


A novel hydrazone, N′-(2,4-dimethoxy benzylidene)-2-hydroxybenzohydrazide

(DBH), which is an analogue of isonicotinic acid (3-hydroxy-naphthalen-2-ylmethylene)-

hydrazide possessing potent anticancer activity has been synthesized and characterized.

The interaction between DBH and bovine serum albumin (BSA) was investigated

systematically by fluorescence, molecular docking, circular dichroism, UV-visible

absorption and electrochemical impedance spectroscopy methods under physiological

conditions. The fluorescence quenching observed is attributed to the formation of a

complex between BSA and DBH and the reverse temperature effect of the fluorescence

quenching has been found and discussed. The effects of iron on the system of DBH-BSA

have also been investigated and found that iron could compete against BSA to bind DBH.

All of these results are supported by a docking study using a BSA crystal model. It is

shown that DBH can efficiently bind with BSA and be transported to the focuses

needed.130

The syntheses and characterization of six copper(II) complexes of 2-

benzoylpyridine benzhydrazone (BPB) in the form of [Cu(BPB)2], [Cu(BPB)Cl]·H2O,

[Cu(BPB)Br], [Cu2(BPB)2](ClO4)2·4H2O, [Cu(BPB)N3]·H2O and [Cu(BPB)NCS]·

H2O·CH3OH were reported by Mangalam et al.131

The crystal structural analysis revealed

that the hydrazone adopts the E conformation about the azo bond and attached to the

metal through the Npy–Nazo–O chelating system.

A new series of homo, heterodinuclear and homotrinuclear copper(II) complexes

containing a new Schiff base ligand (L) and 1,10-phenanthroline were synthesized. Based

on the results of elemental analyses, FT-IR, 1H and

13C NMR spectra, conductivity

measurements and magnetic susceptibility measurements, the complexes were assigned

general compositions {[Cu(L)(H2O)M(phen)2](ClO4)2 [M = Cu(II), Mn(II), Co(II)]} and

{[Cu3(L)2(H2O)2](ClO4)2} with metal:L:phen ratio of 2:1:2 for the dinuclear copper(II)

complexes whereas the metal:L ratio for the trinuclear copper(II) complex was 3:2. The

interaction between these complexes and DNA has also been investigated by agarose gel

electrophoresis and it was found that the homo and heterodinuclear copper complexes can

cleave supercoiled pBR322 DNA to nicked and linear forms in the presence of H2O2.132

29

Introduction


Nickel, copper and zinc complexes of both isatin (H2L1) and N-methylisatin 3-

picolinoyl hydrazone (HL2) were synthesized and characterized by means of

spectroscopic techniques including X-ray diffractometry by Maria et al.133 Biological

studies carried out in vitro on human leukemic cell lines TOM 1 and NB4, have shown

that both ligands and some copper and nickel complexes are active to inhibit cell

proliferation.

N

R O

NN

N

O

N

RO

NN

N

O

M

R = H (or) CH3

Srinivasan et al.134 studied the spectral and redox properties of mixed ligand

complexes of cobalt(III) phenanthroline / bipyridyl-benzoylhydrazones [Co(N-

N)2L](ClO4)2·H2O [where L = anionic form of para-substituted benzaldehyde-

benzoylhydrazone (BHBR); R = H, Me, OMe, OH, Cl or NO2; N-N = 2,2′-bipyridine

(bpy) or 1,10-phenanthroline (phen)] along with their DNA binding and antimicrobial

activity. Binding of these complexes with herring sperm DNA displayed a lower binding

constant value of these complexes with respect to the [Co(phen/bpy)3]3+

due to the polar

interaction of the substituted benzoylhydrazone moiety with the sugar-phosphate

backbone of the DNA. The experimental results indicated that phenanthroline mixed

ligand complexes bound to DNA through an intercalative mode more effectively than

their bipyridine counterparts. These complexes were also found to have good

antimicrobial activity.

30

Introduction


N

N

O

CoN

NN

N

2(ClO4)-

R

where, R = H (or) Me (or) OMe (or) OH (or) Cl (or) NO2

Anticancer activity, structure and theoretical calculation of N-(1-phenyl-3-methyl-

4-propyl-pyrazolone-5)-salicylidene hydrazone (H2L) and its copper(II) complex

[Cu2L2CH3OH]·2CH3OH has been studied by Zhang et al.135 The crystallographic

structural analysis of the complex revealed that the two Cu centers display two different

coordination patterns. The pharmacological result showed that the coordination effect

improves the antitumor activity of the ligand. The calculated Fukui function for H2L and

its deprotonated form L2 predicts that the most probable reactive sites for electrophilic

attack are oxygen atoms and the theoretical data were in good agreement with the

experimental data.

O

N N

O

N N

O

O

CuCuOH3C

H

Binuclear complexes [Zn2(HL1)2(CH3COO)2] (1) and [Zn2(L

2)2] (2) were

synthesized with salicylaldehyde semicarbazones (H2L1) and salicylaldehyde-4-

chlorobenzoyl hydrazone (H2L2) respectively by Parrilha et al.136

Upon recrystallization

of previously prepared [Zn2(HL2)2(Cl)2] (3) in 1:9 DMSO:acetone crystals of

31

Introduction


[Zn2(L2)2(H2O)2]·[Zn2(L

2)2(DMSO)4] (3a) were obtained. The crystal structure of 3a was

also determined. All crystal structures revealed the presence of phenoxo-bridged

binuclear zinc(II) complexes.

ONN

H2N O

Zn

OS

CH3

H3C

O NN

NH2O

Zn

OS

H3C

CH3

1

Complexation of iron(III) with the heterodonor chelating agent 3,5-di-tert-

butylsalicylidene benzoylhydrazine (H2(3,5-tBu2)salbh), in the absence or presence of a

base afforded the complex cation [Fe{H(3,5-tBu2)salbh}2]

+(1) or the neutral compound

[Fe{H(3,5-tBu2)-salbh}{(3,5-

tBu2)salbh}] (2) respectively as revealed by single-crystal

X-ray analyses. Such a synthetic and crystallographic demonstration of the coordination

versatility of an aroylhydrazone towards iron is uncommon. The oxidation and spin states

of the iron have been verified with magnetic and spectroscopic measurements.137

Bu2t

N

HN

OO

Fe

tBu2

NN

OOtBu2

tBu2

Bu2t

N

HN

OO

Fe

tBu2

NNH

OOtBu2

tBu2

1 2

Novel Ln(III) complexes with hesperetin-4-one-(benzoyl) hydrazone (H4L) have

been synthesized and characterized.138

Electronic absorption spectroscopy, fluorescence

spectra, ethidium bromide displacement experiments, iodide quenching experiments, salt

32

Introduction


O

HN N

O

OH

OH

OHH3CO

LnO

NHN

O

HO

HO

HO OCH3

O

ON O

O

ONO

NO3-

where, Ln = La (or) Sm (or) Dy (or) Yb (or) Nd

.

+

effect and viscosity measurements indicated that the ligand and Ln(III) complexes,

especially the Nd(III) complex strongly bind to calf thymus DNA presumably via an

intercalation mechanism. The intrinsic binding constants of the Nd(III) complex and

ligand with DNA were 2.39×106 and 2.7×10

5 M

-1, respectively. Further,, the in vitro

antioxidant activity of the ligand and Ln(III) complexes was determined by superoxide

and hydroxyl radical scavenging method indicated that the ligand and Ln(III) complexes

have the activity to suppress O2-. and HO

. and the Ln(III) complexes were more effective

than the free ligand.

A macrocyclic hydrazone Schiff base synthesized by reacting 1,4-dicarbonyl

phenyl dihydrazide with 2,6-diformyl-4-methyl phenol was treated with Co(II), Ni(II)

and Cu(II) salts and the new complexes have been characterized by elemental analyses,

IR, 1H NMR, UV-visible, FAB mass, EPR spectra, fluorescence, thermal, magnetic and

molar conductance data.139

The electrochemical behavior of the copper(II) complex was

investigated by cyclic voltammetry. EPR spectra of the complex showed the presence of

33

Introduction


O

CH3

NNH

O

NHN

O

O

CH3

NHN

O

NNH

O

M M

Cl

Cl

.(H2O)2

where, M = Co(II) or Cu(II)

O

CH3

NNH

O

NHN

O

O

CH3

NHN

O

NNH

O

Ni Ni

Cl

Cl

.(H2O)2

E

E

where, E = H2O

a considerable covalent character in the metal-ligand bond. The brine shrimp bioassay

was also carried out to study their in vitro cytotoxic properties. The Schiff base and its

complexes have also been screened for their antibacterial and antifungal activities

(Escherichia coli, Staphylococcus aureus, Shigella dysentery, Micrococcus, Bacillus

subtilis, Bacillus cereus, Pseudomonas aeruginosa, Aspergillus niger, Penicillium and

Candida albicans) by MIC method.

Two novel 2-oxo-quinoline-3-carbaldehyde-(4'-hydroxybenzoyl) hydrazone

thiosemicarbazone ligands and their corresponding water soluble Cu(II) complexes were

synthesized and characterised by single crystal X-ray diffraction.140

Interaction of these

Cu(II) complexes with calf thymus DNA (CT DNA) was investigated by electronic

absorption spectroscopy, fluorescence spectroscopy and viscosity measurement. Further,

the in vitro antioxidant activity of the above complexes were determined using hydroxyl

and superoxide radicals.

Metal complexes of 2-methyl-1H-benzimidazole-5-carboxylic acid hydrazide and

its Schiff base, 2-methyl-N-(propan-2-ylidene)-1H-benzimidazole-5-carbohydrazide with

copper, silver, nickel, iron and manganese were prepared and their antitumor activity has

34

Introduction


been studied. Among the complexes, the silver containing one displayed cytotoxicity

(IC50 = 2 μM) against both human lung cancer cell line A549 and human breast cancer

cell line MCF 7.141

35

Introduction


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