1

CHAPTER I

Introduction

Among the various chelating ligands, Schiff bases have been playing an

important role in the development of coordination chemistry. Metal complexes

containing Schiff base ligands have been studied extensively because of their

attractive chemical and physical properties and their wide range of applications in

numerous scientific areas. The steric and electronic effects around the metal core

can be finely tuned by an appropriate selection of bulky and electron withdrawing

or electron donating substituents incorporated into the Schiff bases. Schiff bases

considered as ‘privileged ligands’, are able to stabilize metals in various oxidation

states, are moderate electron donors with a chelating structure and control the

performance of metals in a diverse range of applications including as liquid

crystals1, as molecular switches in logic or memory circuits,

2,3 ultraviolet

stabilizers,4,5

as laser dyes6

and in organic synthesis.7,8

Thiosemicarbazones and semicarbazones are amongst the most widely

studied Schiff base ligands, emerged as an important class of sulfur/oxygen donor

ligands and are conveniently prepared by the condensation of aldehydes or ketones

with thiosemicarbazides/semicarbazides under ambient conditions. Particularly

thiosemicarbazones are of much interest because of their simple preparation,

excellent complexation of not only transition but also non-transition p-elements,

interesting structural characteristics of their complexes, along with the possibility of

their analytical application. This has resulted in a large number of papers and

several reviews that summarized various aspects of the chemistry of these

compounds, such as methods of their synthesis, spectral, magnetic, stereochemical,

structural and other characteristics.9-11

Quinone and quinoid molecules occupy a special position in the areas of

organic and biochemistry.12

The chemistry of metal complexes based on redox-

active ligands such as various quinones and iminoquinones is an extensively studied

area during the last decades. Such interest is mainly caused by the unique ability of

redox-active ligands to the reversible oxidation or reduction in the metal

2

coordination sphere. In this case redox-active ligand serves as an electronic storage

giving numerous variations for the electronic structure of metal complexes.13,14

These quinone compounds served as homogeneous catalysts15

and some are

regarded as models for biological transport reactions.16

In addition, quinones of natural or synthetic origin represent the second

largest class of clinically approved anticancer agents.17-19

Their cytotoxic properties

have been explained through various mechanisms including intercalation, DNA

inhibition, breaking of DNA strands, alterations of cell membrane function and free

radical mediated alkylation.20,21

One of the quinones was β-lapachone, a 1,2-

napthaquinone derivative and a natural product, which inhibited tumor growths in

rats implanted with W-256 carcinoma.22,23

The compound was found to be

cytotoxic to many human cancer cell lines24-26

through inhibition of DNA repair

enzymes.27

Similarly phenanthrenequinone compound has been found to exert cytotoxic

effects in rat hepatoma cell lines (H-4-11-e and Hep G2)28

and possess potent

antimicrobial, anti-inflammatory and antispasmolytic activities.29

This compound

possesses a planar geometry resembling that of phenanthroline-based compounds

which are capable of undergoing intercalating interactions with DNA resulting in

cell antiproliferative activities.30,31

One of the common strategies adopted to

optimize the inhibitory activities of such DNA-acting anticancer agents in a

fragment-based approach of drug design is to append them with a pharmacophore

side chain capable of targeting another protein/factor in the signaling pathways. The

thiosemicarbazide/semicarbazide side chains have been known to possess potent

anticancer activities, probably through selective metal chelation of biologically

relevant trace metal ions or inhibition of ribonucleotide reductase enzyme

obligatory for DNA synthesis. The resulting quinone appended

thiosemicarbazones/semicarbazones and their metal complexes have highly

interesting stereochemical, electronic and electrochemical properties as well as

potentially beneficial biological and catalytic activities.32

3

Biological importance of metal complexes

Transition metal complexes of thiosemicarbazones/semicarbazones are good

source of biologically active chemotherapeutic drugs, play a major role in

improving human welfare and they are utilized for diagnosis, prevention and to cure

diseases.33

Cancer is one of the fatal diseases of death in human beings, which

claims over 6 million people each year worldwide and it is still increasing. The

majority of drugs used for the treatment of cancer today are not cancer cell-specific

and potently cytotoxic against normal cells also. This has forced scientists to

develop novel anticancer agents with fewer side effects and lower levels of

cytotoxicity against normal tissues and cells.34

Metals, in particular transition metals offer potential advantages over the

more common organic-based drugs, including a wide range of coordination

numbers and geometries, accessible redox states, ‘tune-ability’ of the

thermodynamics and kinetics of ligand substitution and a wide structural diversity.

Medicinal inorganic chemistry is a thriving area of research, which was initially

fuelled by the discovery of the metallopharmaceutical cisplatin about 40 years ago.

Although 70% of all cancer patients receive cisplatin during cancer treatment,

chemotherapy with cisplatin and its analogues still has several drawbacks; toxic

side-effects and lack of activity against several types of cancer are problems which

need to be overcome.35

This provides the impetus for the search for anticancer

activity amongst complexes of other metals.

At this juncture, ruthenium, a rare transition metal of the platinum group,

has emerged as an attractive alternative due to several favorable properties suited to

rational anticancer drug design and biological applications. Biologically compatible

ligand-exchange kinetics of RuII

and RuIII

similar to those of platinum complexes, a

higher coordination number that could potentially be used to fine-tune the

properties of the complexes and lower toxicity towards healthy tissues by

mimicking iron in binding to many biological molecules are the advantages of

using ruthenium complexes.36,37

The entrance of two ruthenium based drugs,

NAMI-A38

and KP101939

into clinical trials for the treatment of metastatic tumors

increased the interest in this metal. Both complexes behave quite differently from

4

cisplatin in vivo. In addition, a number of ruthenium compounds were recently

shown to possess very encouraging cytotoxic and antitumor properties in preclinical

models40,41

and are now under active investigation.

In the development of new metal-based therapeutics, a detailed study on the

interactions between DNA and the transition-metal complexes is needed.42

Depending on the exact nature of the metal and ligand, the complexes can bind with

nucleic acid covalently as well as non-covalently.43,44

Therefore, the study on the

interaction of the transition metal complexes with DNA is of great significance for

the design of new drugs before evaluating their anticancer and antioxidant

properties.

Catalytic importance of metal complexes

Transition metal complexes are also used as efficient catalysts in variety of

organic transformations in recent years.45-49

The environment around the

coordination center is an important aspect in the investigation of catalytic activity

exhibited by metal complexes. The catalytic activity of complexes can be well

tuned by the coordinated ligands, either by altering the redox properties of metal or

by insisting the specific activity of ligand to the complexes.50-52

Hence, imparting of

desired ligands in to the coordination sphere of a metal is an interesting part of

coordination chemistry as well as catalysis research.

Transition metal complexes bearing thiosemicarbazones/semicarbazones

have been reported for their excellent catalytic properties in the past few decades.

Among the transition metals, nickel, ruthenium, rhodium complexes are fascinating

due to their reactivity and efficiency in catalysis. The chemistry of nickel

complexes now stands at an important position in useful organic catalytic

reactions.53

Although some toxicity of nickel compounds has been pointed out, they

are inexpensive in comparison with corresponding palladium and platinum

analogues. Further, ruthenium compounds constitute a versatile class of catalysts

for synthetic organic chemistry and feature a large panel of applications.54-56

There

are several aspects that make ruthenium interesting for homogeneous catalysis, such

as its rich coordination chemistry, wide range of oxidation states that it can adopt

5

from -2 to +8 and its ability to accommodate a large variety of ligands in various

coordination geometries. In addition, rhodium complexes have attracted a lot of

attention in the last few decades, mainly due to the metal’s scope and versatility as

homogeneous and heterogeneous catalysts in a large variety of industrial

processes.57-60

The preliminary catalytic screening of complexes received much

importance since they have been a route for the development of useful industrial

catalysts.

Some important catalytic organic transformations

Transition metal catalyzed C-C cross coupling reaction is one of the most

powerful organic transformations for the synthesis of biaryl and alkyne derivatives,

that are structural components of numerous natural products, agrochemicals,

pharmaceuticals and polymers.61-63

Next, the transfer hydrogenation of nitriles is an

important reaction for the large scale synthesis of amines, which are the significant

group of compounds in the chemical and pharmaceutical industries.64

Similarly the

transfer hydrogenation of ketones has emerged as a versatile tool in organic

synthesis which provides practical simplicity, mild reaction conditions and high

selectivities for the preparation of a broad scope of alcohols, as alcohols are key

intermediates in pharmaceuticals, materials and fine chemicals.65-67

On the other hand oxidation of alcohols to the corresponding carbonyl

compounds plays an important role in organic synthesis and in the fine

chemicals industry, often being a key step for the preparation of important synthons

or directly affording fine chemicals and valuable specialty products such as

fragrances, drugs, vitamins and hormones.68-70

In addition, 2-oxazolines are an

important class of heterocycles and are versatile intermediates in synthetic organic

chemistry. They have been found in a variety of biologically active natural

products.71,72

Further, the asymmetric nitroaldol (Henry) reaction provides direct

access to chiral β-nitro alcohols, which are synthetic precursors of bioactive

compounds. Moreover, the nitro group in the product can further converted into

several other functionalities to give synthetically and biologically important bi-

functional compounds.73,74

6

Based on the above, the present thesis deals on the synthesis and

characterization of nickel, ruthenium and rhodium complexes bearing quinone

based thiosemicarbazone/semicarbazone ligands. Further, the newly synthesized

complexes were subjected to biological or catalytic investigations depending upon

the nature of metal, coordinated chelating ligand and coligands.

Literature survey

Thiosemicarbazones and semicarbazones are known for their wide

spectrum of biological and catalytic activities apart from their good complexing

properties. The study on the coordination behavior of various thiosemicarbazones/

semicarbazones and their applications are quite interesting area of research

for the last few decades. The coordination modes of thiosemicarabazone

and semicarbazone ligands play a vital role in the stability, geometry and structural

properties of the complexes. The literature survey has essentially focused on the

structure-activity relationships of metal complexes. Here, some of the interesting

and important literatures was discussed which dealt with synthesis, structure and

application studies of nickel, ruthenium and rhodium complexes containing

thiosemicarbazone/semicarbazone ligands in a brief manner.

Nickel complexes

Milenkovic et al.75

have described the synthesis and characterization of

square-planar complexes of nickel(II) with condensation derivative of 2-

(diphenylphosphino)benzaldehyde and 4-phenylsemicarbazide and monodentate

pseudohalides. Investigated complexes exhibited moderate antibacterial and

cytotoxic activity. Complexes and ligand induced concentration dependent cell

cycle arrest in the S phase as well as decrease of percentage of cells in G1 phase,

without significant increase of apoptotic fraction of cells. The interaction of the

complexes and ligand with CT-DNA results in changes in UV-Vis spectra typical

for non-covalent bonding. The results of DNA cleavage experiments showed that

complexes produce nicked supercoiled plasmid DNA.

7

Reactions76

of 5-bromo-2-hydroxy-benzaldehyde-S-R-4-R1-thiosemi

carbazones, [R, R1

= H, H (L1); CH3, H (L2); H, C6H5 (L3); CH3, C6H5 (L4)] with

[Ni(PPh3)2Cl2] in 1:1 molar ratio yielded complexes of general formula

[Ni(L)(PPh3)] (1-3). The complexes 1 and 3 involve the ONS donor set of the

thiosemicarbazone while the complex 2 utilize the ONN set. The reaction of L4 and

the nickel salt gave the complex 3 by loss of the CH3 group from the sulfur. The

complexes were characterized by physicochemical and spectroscopic methods. The

structures of the representative complexes have been determined by single crystal

X-ray diffraction and a new coordination mode (ONN) of salicylaldehyde

thiosemicarbazones has been identified.

[(ML)2(bipy)] complexes (L = thiosemicarbazone of 2-hydroxy

benzaldehyde, M = Ni(II) or Cu(II)) were reported by Kolotilov et al.77

Nickel

complex possessed porous structure due to peculiarities of crystal packing whereas

copper complex formed infinite zig-zag chains with dense non-porous packing.

New nickel(II) complex containing p-[N,N-bis(2-chloroethyl)amino]

benzaldehyde-4-methyl thiosemicarbazone has been synthesized by Anitha et al.78

The crystal structure of the free ligand and complex has been determined by single

crystal X-ray diffraction technique. In the complex, thiosemicarbazone ligand is

coordinated to nickel through SNNS mode. The complex has been tested for their

antibacterial activity against various pathogenic bacteria. From this study, it was

found that the activity of complex reaches the effectiveness of the conventional

bacteriocide Streptomycin when compared to simple ligand.

Convenient synthesis of a new square planar nickel(II) naphthaldehyde

thiosemicarbazone complex has been described79

and the composition of the

complex has been established by elemental analyses, spectral methods and single

crystal X-ray crystallography. The new complex acts as an active homogeneous

catalyst for the Mizoroki-Heck reaction of electron deficient and electron rich aryl

bromides with various olefins under optimized conditions.

The synthesis and characterization of new mixed-ligand nickel(II)

complexes of 4-(p-X-phenyl) thiosemicarbazones of salicylaldehyde (X = F, Br,

8

OCH3) were described by Saswati et al.80

The molecular structure of the complexes

has been determined by X-ray crystallography. The complexes have been screened

for their antibacterial activity against Escherichia coli and Bacillus. The minimum

inhibitory concentrations of these complexes and their antibacterial activities

indicate that the complexes were the potential lead molecules for drug designing.

Priyarega et al.81

have reported the synthesis and characterization of new

nickel(II) complexes of the general formula [Ni(PPh3)(L)] (L = 4-diethylamino-

salicylaldehyde N(4)-substituted thiosemicarbazone). Molecular structure of a

representative complex has been determined by X-ray crystallography. Catalytic

activity of the complexes has been explored for aryl-aryl coupling reaction.

New mixed-ligand copper(II) and nickel(II) complexes with general formula

[M(L1)L2] (M = Cu2+

or Ni2+

, L1 = salicylaldehyde-4-methylthiosemicarbazone, L2

= imidazole or benzimidazole) were reported by Ain Mazlan et al.82

The

spectroscopic data indicated that the Schiff bases behave as a tridentate ONS donor

ligand coordinating via the phenolic oxygen, azomethine nitrogen and thiolate

sulfur atoms. Molar conductance values indicate that the metal complexes were

essentially non-electrolytes in DMSO solution. X-ray crystallography of the

representative complexes shows that square planar geometry around the metal(II)

ions. The copper(II) complexes were active against MDA-MB-231 and MCF-7

breast cancer cell lines whereas the nickel(II) complexes were inactive.

Reaction of salicylaldehyde/2-hydroxyacetophenone/2-hydroxy

naphthaldehyde thiosemicarbazone (L) with Ni(ClO4)2.6H2O afforded dimeric

complexes of type [{Ni(L)}2].83

Reaction of these complexes with

triphenylphosphine (PPh3), pyridine (py) and 4,4′-bipyridine (bpy) has yielded

complexes of type [Ni(L)(PPh3)], [Ni(L)(py)] and [{Ni(L)}2(bpy)] respectively,

those have also been obtained from reaction of the thiosemicarbazones with

Ni(ClO4)2.6H2O and PPh3 or pyridine or 4,4ʹ-bipyridine. In all these complexes

thiosemicarbazone is coordinated to nickel as ONS-donor. All these complexes

show characteristic 1H NMR spectra and intense absorptions in the visible and

ultraviolet region. Cyclic voltammetry on the complexes shows one irreversible

oxidation on the positive side of SCE and one irreversible reduction on the negative

9

side. The mixed-ligand nickel complexes were found to be efficient catalysts for

Heck type C-C coupling reactions. In vitro cytotoxicity screening of the complexes

has also been carried out in a human tumor cell lines, viz. breast carcinoma cell line

(MCF-7). An apoptosis study in MCF-7 with all the complexes confirms that at

concentrations near LD50 they induce apoptosis.

New nickel(II) thiosemicarbazone complexes containing triphenylphosphine

namely [Ni(L1)(PPh3)] and [Ni(L2)(PPh3)] (L1 = salicylaldehyde-N(4)-methyl

thiosemicarbazone and L2 = 2-hydroxy-1-naphthaldehyde-N(4)-methylthiosemi

carbazone) have been reported by Prabhakaran et al.84

The crystal structure of the

complexes has been determined by single crystal X-ray diffraction technique. In all

the complexes the thiosemicarbazone ligand coordinated to nickel through ONS

mode. The electrochemical behavior of the complexes has been investigated by

cyclic voltammetry in acetonitrile. The new complexes were subjected to test their

DNA topoisomerase II inhibition efficiency. The complexes showed 95%

inhibition. The observed inhibition activity was found to be more potent than the

activity of conventional standard Nalidixic acid.

Muthu Tamizh et al.85

have reported the synthesis and characterization of

air stable nickel(II) and palladium(II) complexes viz. [Ni(LS)(P(OEt)3)],

[Ni(LN)(P(OEt)3)], [Pd(LS)(P(OEt)3)] and [Pd(LN)(P(OEt)3)] (LS/LN = N-(2-

mercaptophenyl) salicylideneimine/naphthylideneimine). The 1H-

31P HMBC spectrum

established the coupling of phosphorus with the azomethine proton of the Schiff base

and the aliphatic protons of triethylphosphite. The nickel(II) and palladium(II)

complexes exhibited good catalytic activity in Kumada-Tamao-Corriu and Suzuki-

Miyaura coupling reactions respectively.

A series of novel nickel(II) thiosemicarbazone complexes have been

reported by Kalaivani et al.86

Further, their efficacy to interact with CT-DNA/BSA

has been explored. The complexes bound with CT-DNA by intercalation mode.

Moreover, static quenching was observed for their interaction with BSA. The new

complexes were tested for their in vitro cytotoxicity against human lung

adenocarcinoma (A549) cell line. The results showed that the new complexes

exhibited significant degree of cytotoxicity at given experimental condition.

10

Further, the results of LDH and NO release supported the cytotoxic nature of the

complexes. The observed cytotoxicity of the complexes may be routed through

ROS-hypergeneration and lipid-peroxidation with subsequent depletion of cellular

antioxidant pool (GSH, SOD, CAT, GPx and GST) resulted in the reduction of

mitochondrial-membrane potential, caspase-3 activation and DNA fragmentation.

The data disclose that the complexes could induce apoptosis in A549 cells through

mitochondrial mediated fashion and inhibited the migration of lung cancer cells and

by metastasis.

The coordination behavior of ferrocenylthiosemicarbazone (L) was

investigated in a trinuclear [Ni(L)2] complex.87

The structure of the complex has

been studied by X-ray crystallography. The complex crystallized in rhombohedral

with six molecules per unit cell which has the dimensions of a = 28.8042(2) Å, b =

28.8042(2) Å and c = 19.5131(3) Å, α = 90°, β = 90°, γ = 120°. The electronic

communication between the metal centers has been studied by cyclic voltammetry.

The structure optimizations of 2-formylpyridine/3-formylpyridine/4-

formylpyridine semicarbazone complexes with cobalt(II), nickel(II) and zinc(II)

were carried out using DFT calculations at the B3LYP/LANL2DZ level of theory.88

The B3LYP/LANL2DZ-optimized geometry parameters of the complexes show

good agreement with their corresponding X-ray crystallographic data. The reaction

energies and thermodynamic properties of complexation for these complexes

computed at the same level of theory.

The reaction of nickel(II) chloride and bromide with 3-thiophene aldehyde

semicarbazone (L1) and 2,3-thiophene dicarboxaldehyde bis(semicarbazone) (L2)

leads to the formation of a series of new complexes was reported by Alomar et al.89

The crystal structure of the ligands and of the representative complex has been

determined by X-ray diffraction method. For all these complexes, the central ion

was coordinated through the oxygen atom of the carbonyl and the azomethine

nitrogen atom of the semicarbazone. The antifungal activity of the complexes and

their corresponding ligands was evaluated against some strains of respectively,

Candida albicans, Candida glabrata and Aspergillus fumigatus. The complexes

11

revealed interesting CMI80 values specifically against C. glabrata. Cytotoxicity

assay was also carried out in vitro on MRC5 cells.

Chandra et al.90

have described the synthesis and characterization of

cobalt(II), nickel(II) and copper(II) complexes containing pyrole-2-

carboxyaldehyde thiosemicarbazone/semicarbazone. These complexes were

characterized by elemental analyses, molar conductance, magnetic susceptibility

measurements, mass, IR, UV-Vis and EPR spectral studies. All the complexes were

of high-spin type. On the basis of spectral studies an octahedral geometry may be

assigned for cobalt(II) and nickel(II) complexes. A tetragonal geometry may be

suggested for copper(II) complexes.

Cobalt(II), nickel(II) and copper(II) complexes were synthesized with

thiosemicarbazone and semicarbazone derived from 2-acetyl furan.91

These

complexes were characterized by spectral techniques. The molar conductance

measurements of the complexes in DMSO correspond to non-electrolytic nature.

All the complexes were of high-spin type. On the basis of spectral studies an

octahedral geometry may be assigned for cobalt(II) and nickel(II) complexes

whereas tetragonal geometry for copper(II) complexes.

Barros-Garcia et al.92

have synthesized a new ligand 2-acetyl-2-thiazoline

semicarbazone (L) and its metal complexes [CuCl2(L)] and [Ni(L)2](NO3)2. The

structure of complexes has been determined by X-ray diffraction. In both

complexes, the Schiff base acts as a tridentate ligand through N(1), N(2) and O

atoms, making two five-membered chelate rings. The copper complex consists of

monomeric molecules in which the copper atom was five coordinated in a distorted

square-pyramidal geometry, with one ligand and two chlorine ligands. The complex

cation of nickel possesses approximately a non-crystallographic C2 symmetry. The

environment around the nickel atom may be described as a distorted octahedral

geometry with the metallic atom coordinated to two ligands.

Kandemirli et al.93

have reported the synthesis and characterization of

5-methoxyisatin-3-(N-cyclohexyl) thiosemicarbazone and its zinc(II) and nickel(II)

complexes. The possible structures and IR data of the studied molecules were

12

calculated and compared with experimental results using B3LYP/6-31G(d,p) and

B3LYP/LANL2DZ methods.

Cobalt(II) and nickel(II) complexes of general composition ML2X2 (X = Cl-,

NO3-) were synthesized by the condensation of metal salts with

semicarbazone/thiosemicarbazone derived from 2-acetyl coumarone.94

The ligands

and metal complexes were characterized by spectral studies. On the basis of

electronic, molar conductance and infrared spectral studies, the complexes were

found to have square planar geometry. The Schiff bases and their metal complexes

were tested for their antibacterial and antioxidant activities.

Abou-Melha et al.95

have studied the cobalt(II) and nickel(II) complexes

containing the semicarbazone and thiosemicarbazone Schiff-bases formed from

4-hydroxycoumarin-3-carbaldehyde. The nature of bonding and the stereochemistry

of the complexes have been deduced from elemental analyses, infrared, electronic

spectra, magnetic susceptibility and conductivity measurements. An octahedral

geometry has been suggested for the complexes. The metal complexes were

screened for their antifungal and antibacterial activities on different species of

pathogenic fungi and bacteria. The biopotency has also been discussed.

A new ligand, 6-hydroxy chromone-3-carbaldehyde thiosemicarbazone and

its nickel(II) complex have been studied by Wang et al.96

The crystal structure of

complex was determined by single crystal X-ray diffraction. Complex and ligand

were subjected to biological tests in vitro using THP-1, Raji and Hela cancer cell

lines. Compared with the ligand, nickel(II) complex showed significant cytotoxic

activity against these three cancer cell lines. The interaction of complex and ligand

with calf thymus DNA was then investigated by spectrometric titration, ethidium

bromide displacement experiments and viscosity measurements methods. The

experimental results indicated that nickel(II) complex bound to DNA by

intercalative mode via the ligand.

Guveli et al.97

have studied the complexes of the type [Ni(L1)(PPh3)] (1) and

[Ni(L2)(PPh3)]·HCl (2) (L = 2-hydroxyacetophenone-S-R-4-R1-thiosemicarbazones

(R/R1: H/CH3 (L1), CH3/H (L2)). In both the complexes, the thiosemicarbazone

13

ligands coordinate to nickel(II) by giving two protons. The complex 1 was formed

through the phenolate oxygen, azomethine nitrogen and sulfur atoms of L1 and the

P atom of a triphenylphosphine ligand. In the complex 2, L2 was functional through

an ONN donor set, containing thioamide nitrogen instead of a sulfur atom. X-ray

analysis indicated distorted square planar structure for the complexes and the nickel

atom lie slightly above the planes structured by the donor atoms.

Dinuclear nickel(II) complexes with 2-hydroxyacetophenone N(4)-

substituted thiosemicarbazones have reported by West et al.98

Both the

thiosemicarbazones and their nickel(II) complexes have considerable growth

inhibitory activity against Paecilomyces variotii, but none against Aspergillus niger.

The crystal structure of representative complex was also studied.

Mathan Kumar et al.99

have synthesized a new kind of nickel(II) complex of

the type, [Ni(PPh3)(L)] (L = 2-(3-bromo-5-chloro-2-hydroxybenzylidene)-N-

phenyhydrazine-carbothio amide). Based on spectroscopic and X-ray

crystallographic studies, a square planar structure has been proposed for the

nickel(II) complex. The interaction between complex and CT-DNA has been

investigated using UV-Vis, circular dichroism studies and gel electrophoresis. In

UV studies, the observed strong hypochromism in absorption intensities and

binding constant value (Kb = 1.8 × 105) indicates significant interaction between the

electronic states of the nickel(II) complex chromophore with that of DNA bases.

The observations suggest that the complex bind to DNA through a non-intercalative

mode due to the waggling of three phenyl rings of triphenyl phosphine group. The

nickel(II) complex display significant hydrolytic cleavage of circular plasmid

pUC18 DNA. The newly synthesized thiosemicarbazone compound is a promising

system for the development of new colorimetric probes for the detection of anions.

Anion sensing ability of the receptor (L) with halide ions (F-, Cl

-, Br

- and I

-) have

been carried out in different solvents. The receptor shows a remarkable color

change from colorless to dark orange in CH3CN solution on selective binding with

fluoride ion. The anion recognition property of the receptor via hydrogen bonding

interactions was monitored by UV-Vis titration and 1H NMR spectroscopy.

14

Leovac et al.100

have described the synthesis of the nickel(II) complexes

with pyridoxal semicarbazone (L1) (1-4) as well as complexes with pyridoxal

thiosemicarbazone (L2) (5,6). Complexes 1-3 were paramagnetic and have most

probably an octahedral structure, for complex 2 this was proved by X-ray

diffraction analysis. In contrast, complexes 4-6 were diamagnetic and have a

square-planar structure and in the case of complex 5 this was also confirmed by X-

ray structural analysis. In all cases the Schiff bases were coordinated as tridentate

ligands with an ONX (X = O (L1), S (L2)) set of donor atoms.

Reaction101

of aqueous solutions of Ni(NO3)2 and pyridoxal semicarbazone

(L1) in the presence of NaN3 afforded two complexes, viz. green, paramagnetic

binuclear octahedral [Ni2(L1)2(µ1,1-N3)2(N3)2].2H2O and red, octahedral [Ni(L1)2].

2H2O complex. Under the same reaction conditions, pyridoxal thiosemicarbazone

(L2) gave only one diamagnetic square planar, red complex [Ni(L2)N3].H2O. In the

absence of NaN3, the reaction of L2 and Ni(NO3)2 yielded brown paramagnetic

octahedral complex [Ni(L2)2](NO3)2.H2O. The complexes were characterized by

elemental analyses and spectral techniques. The crystal structure of complexes was

also confirmed by X-ray mono crystal diffraction method.

Manikandan et al.102

have synthesized nickel(II) complexes from the

reaction of [NiCl2(PPh3)2] with the tridentate Schiff base ligand, pyridoxal

thiosemicarbazone (L1), pyridoxal N-methyl thiosemicarbazone (L2) and pyridoxal

N-phenyl thiosemicarbazone (L3) in ethanol. These complexes have been

characterized by elemental analyses and spectroscopic methods. The molecular

structure of representative complex was determined by single-crystal X-ray

diffraction, which reveals a distorted square planar geometry around the nickel(II)

ion. The nitroaldol reaction was studied using the nickel(II) complexes as catalysts

in a homogeneous solution formed by an ionic liquid and methanol. The effect of

solvent, ionic liquid, time, temperature, catalyst loading and substituent of the

ligand moiety on the reaction was also studied. A two step substrate addition

mechanism was tentatively proposed based on ESI-Mass spectral monitoring of the

reaction mass.

15

Nickel(II) complexes of o-naphthaquinone thiosemicarbazone and

semicarbazone were synthesized by Afrasiabi et al.32a

The X-ray crystal structure of

both the complexes describes a distorted octahedral coordination with two

tridentate mono deprotonated ligands. In vitro anticancer studies on MCF-7 human

breast cancer cells reveal that the semicarbazone derivative along with its nickel

complex was more active in the inhibition of cell proliferation than the

thiosemicarbazone analogue.

Copper(II), nickel(II), palladium(II) and platinum(II) complexes of o-

naphthaquinone thiosemicarbazone were synthesized and characterized by

spectroscopic studies.32b

In both solution (NMR) and solid state (IR, single-crystal

X-ray diffraction determination), the free ligand exists as thione form. The

nickel(II) complex shows 1:2 metal to ligand stoichiometry while the other

complexes exhibit 1:1 metal-ligand compositions. In vitro anticancer studies on

MCF7 human breast cancer cells reveal that adding a thiosemicarbazone

pharmacophore to the parent quinone carbonyl considerably enhances its

antiproliferative activity. Among the metal complexes, the nickel complex exhibits

the lowest IC50 value suggesting a different mechanism of action involving

inhibition of topoisomerase II activity.

Afrasiabi et al.32c

have described the synthesis and characterization of

thiosemicarbazone derivative of 9,10-phenanthrenequinone and its metal

complexes. Its copper complex shows 1:1 stoichiometry while nickel and cobalt

complexes show 1:2 stoichiometries. The X-ray crystal structure of the nickel

complex indicates two tridentate ligands coordinating in the thiolato form yielding

an octahedral geometry for the ‘mer’ isomer. The copper complex exhibits

maximum antiproliferative activity against human breast cancer cell-line, T47D

probably due to inhibition of steroid binding to the cognative receptor or by

preventing dimerization of the estrogen receptor.

Ruthenium complexes

The synthesis and characterization of ruthenium(II) thiosemicarbazone of

the type [Ru(PPh3)2(L)2] from the reaction of substituted benzaldehyde

16

thiosemicarbazone ligands (L) and [Ru(PPh3)2Cl2] was reported by Basuli et al.103

From the single crystal X-ray structure it was confirmed that the ligands coordinate

to the metal centre via the hydrazinic nitrogen and the thiolate sulfur forming four-

membered chelate rings and the two PPh3 ligands occupy the cis position. The

complexes displayed several intense absorptions in the visible regions attributed to

metal-to-ligand charge transfer (MLCT) transitions and metal-centred two oxidative

responses.

Basuli et al.104

have described the synthesis and characterization of cationic

ruthenium(II) bipyridyl thiosemicarbazone complexes containing benzaldehyde or

acetone thiosemicarbazone ligands. All the complexes show several intense MLCT

transitions in the visible region. The structure of representative complexes was

confirmed by X-ray crystallography. The benzaldehyde thiosemicarbazone ligand

binds to the ruthenium(II) ion via the hydrazinic nitrogen and the thiolate sulfur

forming a four-membered ring whereas the acetone thiosemicarbazone ligand binds

to the ruthenium(II) ion via azomethine nitrogen and thiolate sulfur forming a five-

membered ring. The difference in coordination modes of the ligands was attributed

to the difference in steric in the ligand.

Variable coordination modes of benzaldehyde thiosemicarbazones in

ruthenium(II) complexes were reported by Dutta et al.105

Reaction of benzaldehyde

thiosemicarbazones (H2LR) with [Ru(PPh3)2(CO)2Cl2] under different experimental

conditions afforded monomeric [Ru(PPh3)2(CO)(HLR)(H)] and dimeric

[Ru2(PPh3)2(CO)2(LR)2] complexes. The crystal structure of a representative

monomeric complex indicates that the ligand was coordinated to the ruthenium(II)

centre as a bidentate N,S-donor ligand forming a four-membered chelate ring. The

molecular structure of a representative dimeric complex indicates that each ligand is

coordinated to one ruthenium(II) centre, by dissociation of the two protons, as a

dianionic tridentate C,N,S donor ligand, forming two five-membered chelate rings

and at the same time the sulfur atom of each ligand was also bonded to the second

ruthenium(II) centre. The complexes display two metal-centred oxidations in both

the series.

17

Reaction106

of five 4(R)-benzaldehyde thiosemicarbazones (R = OCH3,

CH3, H, Cl and NO2) with [Ru(H)Cl(CO)(PPh3)3] in refluxing methanol in the

presence of a base (NEt3) affords complexes of two different types, viz. 1-R and 2-

R. In the 1-R complexes the thiosemicarbazone was coordinated to ruthenium as a

dianionic tridentate C,N,S-donor via C-H bond activation. Two triphenylphosphines

and a carbonyl were also coordinated to ruthenium. The tricoordinated

thiosemicarbazone ligand was sharing the same equatorial plane with ruthenium

and the carbonyl and the PPh3 ligands were mutually trans. In the 2-R complexes

the thiosemicarbazone ligand was coordinated to ruthenium as a monoanionic

bidentate N,S-donor forming a four-membered chelate ring with a bite angle of

63.91(11)°. Two triphenylphosphines, a carbonyl and a hydride were also

coordinated to ruthenium. The coordinated thiosemicarbazone ligand, carbonyl and

hydride constitute one equatorial plane with the metal at the center, where the

carbonyl was trans to the coordinated nitrogen of the thiosemicarbazone and the

hydride was trans to the sulfur. The two triphenylphosphines were trans to each

other. Structure of representative complexes has been determined by X-ray

crystallography. All the complexes show intense transitions in the visible region,

which were assigned, based on DFT calculations, to transitions within orbitals of

the thiosemicarbazone ligand. Cyclic voltammetry on the complexes shows two

oxidations of the coordinated thiosemicarbazone on the positive side of SCE and a

reduction of the same ligand on the negative side.

Malecki et al.107

reported the combined experimental and computational

study of ruthenium(II) carbonyl complexes containing thiosemicarbazone ligands.

Five novel [Ru(H/Cl)(L)(PPh3)2] complexes have been obtained and characterized

by IR, UV-Vis, NMR spectroscopy and X-ray crystallography. Their electronic

structures have been determined using the density functional theory (DFT) method.

The donor-acceptor properties of the ligands were correlated with the substituent

positions on the benzene ring. The luminescence properties of the complexes have

also been examined.

18

Neutral mixed ligand thiosemicarbazone complexes of ruthenium having

general formula [Ru(PPh3)2L2] (L = 1-(arylidine) 4-aryl thiosemicarbazones) have

been synthesized and characterized by Mishra et al.108

All complexes were

diamagnetic and hence ruthenium was in the +2 oxidation state (low-spin d6, S = 0).

The complexes show several intense peaks in the visible region due to allowed

metal to ligand charge transfer transitions. The structure of the complexes has been

determined by single-crystal X-ray diffraction and they show that

thiosemicarbazone ligands coordinate to the ruthenium center through the

hydrazinic nitrogen and sulfur forming four membered chelate rings with ruthenium

in N2S2P2 coordination environment. In dichloromethane solution, the complexes

show two quasi-reversible oxidative responses corresponding to loss of electron

from HOMO and HOMO-1. The E0

values of the above two oxidations shows good

linear relationship with Hammett substituents constant (σ) as well as with the

HOMO energy of the molecules calculated by the EHMO method. A DFT

calculation on one representative complex suggests that there is appreciable

contribution of the sulfur p-orbitals to the HOMO and HOMO-1.

N(4)-Methyl-4-nitrobenzaldehyde thiosemicarbazone (L1), N(4)-methyl-4-

nitrobenzophenone thiosemicarbazone (L2) and their ruthenium(II) complexes

[Ru(L1)2(PPh3)2], [Ru(L2)2(PPh3)2], [Ru(L1)2(dppb)] and [Ru(L2)2(dppb)] (dppb =

1,4- bis(diphenylphospine) butane) were obtained and characterized by Rodrigues

et al.109

The crystal structure of L1 has been determined. Electrochemical studies

have shown that the nitro anion radical, one of the proposed intermediates in the

mechanism of action of nitro-containing anti-trypanosomal drugs, was formed at

approximately -1.00 V in the free thiosemicarbazones as well as in their

corresponding ruthenium(II) complexes, suggesting their potential to act as

antitrypanosomal drugs. The natural fluorescence of ligands and complexes

provides a way to identify and to monitor their concentration in biological systems.

A series of new hexa-coordinated ruthenium(II) complexes of the type

[Ru(CO)(EPh3)(B)(L)] (E = P or As; B = PPh3, AsPh3 or py; L = chalcone

thiosemicarbazone) have been prepared by Muthukumar et al.110

The new

complexes have been characterized by analytical and spectroscopic (IR, UV-Vis,

19

NMR) methods. On the basis of data obtained, an octahedral structure was assigned

for all of the complexes. The chalcone thiosemicarbazones behave as dianionic

tridentate O, N, S donors and coordinate to ruthenium via the phenolic oxygen of

chalcone, the imine nitrogen of thiosemicarbazone and thione sulfur. The new

complexes exhibit catalytic activity for the oxidation of primary and secondary

alcohols to their corresponding aldehydes and ketones and they were also found to

be efficient catalysts for the transfer hydrogenation of carbonyl compounds.

Mutkukumar et al.111

reported new six-coordinate ruthenium(III) complexes

of the type [RuX(EPh3)2(L)] (X = Cl or Br; E = P or As; L = chalcone

thiosemicarbazone) by reacting [RuX3(EPh3)3] with chalcone thiosemicarbazones in

benzene under reflux. The new complexes have been characterized by analytical

and spectroscopic (IR, electronic, mass, EPR) data. The redox behavior of the

complexes has also been studied. Based on the above data, an octahedral structure

has been assigned for all the complexes. The new complexes exhibit catalytic

activity for carbon-carbon coupling reactions.

An unusual coordination mode of salicylaldehyde N-

phenylthiosemicarbazone ligand was observed in unusual ruthenium(III) carbonyl

complex112

for the first time when it was reacted with [RuHCl(CO)(PPh3)3]. The

EPR and electrochemical analysis confirmed the formation of Ru(III) species.

Kalaivani et al.113

have studied the reaction of salicylaldehyde

thiosemicarbazone (H2L) with an equimolar amount of [RuHCl(CO)(PPh3)3]. It has

afforded two complexes, namely [Ru(HL)(CO)Cl(PPh3)2] (1) and

[Ru(L)(CO)(PPh3)2] (2) in one pot. The new complexes were separated and

characterized by elemental analyses, various spectroscopic techniques (IR, UV-Vis,

NMR), X-ray crystallography and cyclic voltammetry. In complex 1, the ligand

coordinated in a bidentate monobasic fashion by forming an unusual strained NS

four-membered ring in 32% yield. However, in 2, the ligand coordinated in a

tridentate dibasic fashion by forming ONS five- and six-membered rings in 51%

yield. Comparative biological studies such as DNA binding, cytotoxicity (MTT,

LDH, and NO) and cellular uptake studies have been carried out for new

ruthenium(II) complexes. From the DNA binding studies, it was inferred that the

20

complex 1 exhibited electrostatic binding and 2 exhibited intercalative binding

modes. On comparison of the cytotoxicity of the complexes in human lung cancer

cells (A549) and liver cancer cells (HepG2), the complex 2 exhibited better activity

than 1. This may be due to the strong chelation and subsequent electron

delocalization in 2 increasing the lipophilic character of the metal ion into cells.

Prabhakaran et al.114

have reported the synthesis and characterization of bis

salicylaldehyde-4(N)-ethylthiosemicarbazone ruthenium(III) triphenylphosphine

[Ru(L)(HL)(PPh3)] and it showed 100% inhibition on the DPPH radical. It also

exhibited a significant lymphocyte activity and inhibitory effect on the lung

carcinoma A549 cell.

Kalaivani et al.115

reported the reaction of [RuHCl(CO)(PPh3)3] with an

equimolar amount of salicylaldehyde-4(N)-methylthiosemicarbazone (H2L) resulted

in two entities, namely [Ru(HL)Cl(CO)(PPh3)2] (1) and [Ru(L)(CO)(PPh3)2] (2)

from a single tub. The new complexes were characterized by various spectral (IR,

UV-Vis, NMR), analytical and single crystal X-ray diffraction studies. From the

crystallographic studies, it was confirmed that in the complex 1, the ligand

coordinated through the thiolate sulfur and the deprotonated hydrazinic nitrogen

N(2), resulting in the formation of an unusual strained four membered chelate ring.

The third potential donor, phenolic oxygen, remained uncoordinated. In the

complex 2, the ligand coordinated as an ONS chelate with the formation of more

common five and six membered chelate rings. Complexes have been tested for their

DNA/protein binding properties by taking CT-DNA/lysozyme as models. From the

protein binding studies, the alterations in the secondary structure of lysozyme by

the ruthenium(II) complexes were confirmed with synchronous and three

dimensional fluorescence spectroscopic studies. The in vitro cytotoxicity of the

newly synthesized complexes was carried out in two different human tumor cell

lines, A549 and HepG2. The cytotoxicity studies showed that the complex 2

exhibited higher activity than 1.

Selvamurugan et al.116

have reported the synthesis and characterization of a

series of hexa-coordinated ruthenium(II) complexes of the type [Ru(CO)(B)Ln] by

reacting dibasic quadridentate Schiff base ligands H2Ln (n = 1-4) with starting

21

complexes [RuHCl(CO)(EPh3)2(B)] (E = P or As; B = PPh3, AsPh3 or py). The

synthesized complexes were characterized using elemental and various spectral

studies including IR, UV-Vis, NMR and mass spectroscopy. An octahedral

geometry was tentatively proposed for all the complexes based on the spectral data

obtained. The experiments on antioxidant activity showed that the ruthenium(II)

S-methylisothiosemicarbazone Schiff base complexes exhibited good scavenging

activity against various free radicals (DPPH, OH and NO). The in vitro cytotoxicity

of these complexes has been evaluated by MTT assay. The results demonstrate that

the complexes have good anticancer activities against selected cancer cell line,

human breast cancer cell line (MCF-7) and human skin carcinoma cell line (A431).

The DNA cleavage studies showed that the complexes have better cleavage of pBR

322 DNA.

A series of new ruthenium(II) complexes were synthesized117

with Schiff

bases derived from salicylaldehyde/o-hydroxyacetophenone/o-vanillin/2-hydroxy-

1-naphthaldehyde with thiosemicarbazide and acetyl furan. They were

characterized by elemental analyses, IR, UV-Vis, NMR and mass spectral studies.

The elemental analyses suggests the stoichiometry to be 1:1 (metal:ligand). Four of

these complexes were tested for its binding with CT-DNA using absorption

spectroscopic studies and two of these complexes exhibit efficient DNA cleavage

activity.

Reaction118

of 4-phenylthiosemicarbazone of salicylaldehyde/o-

hydroxyacetophenone ligand (L) with [Ru(PPh3)3Cl2] in refluxing methanol

furnished ruthenium(II) complexes of general formula [Ru(PPh3)2(L)Cl] where the

ligands acted as monoanionic tridentate ONS donors attached to the ruthenium(II)

through the deprotonated phenolic oxygen, thione sulfur and azomethine nitrogen.

The reaction119

of cis-[RuCl2(DMSO)4] with salicylaldehyde semicarbazone

in ethanol resulted in the chemoselective cleavage of the C=N bond of the Schiff

base, forming a complex in which the semicarbazide remains coordinated to the

metal. In another set of reactions of cis-[RuCl2(DMSO)4] with 4-aminoantipyrine

derivatives of salicylaldehyde, 2-hydroxy-1-naphthaldehyde and o-vanillin, C=N

cleavage was observed in all three cases yielding the same compound,

22

[RuCl2(DMSO)2(4-aminoantipyrine)]. However, when the reactions, under the

same experimental conditions, were extended to unsubstituted/N-substituted

thiosemicarbazones of salicylaldehyde and 2-hydroxy-1-naphthaldehyde, no

cleavage was observed. All the new complexes were characterized by analytical and

spectroscopic techniques. The structure of the representative complexes was

determined by single crystal XRD. The electrochemistry of the complexes was

studied by cyclic voltammetry. Further, the preliminary DNA-binding ability and

antibacterial activity of the complexes were studied.

In an attempt to synthesize ruthenium(II)-DMSO-thiosemicarbazone

complexes,120

a series of carbonyl compounds were selected to condense with

thiosemicarbazide in ethanol in order to get the respective thiosemicarbazone ligand

as the first step. All the selected carbonyl compounds yielded the expected

thiosemicarbazone ligand, but the product obtained by the reaction of benzaldehyde

with thiosemicarbazide in ethanol was found to show sharp IR peak characteristic

of C=O group and thought to be benzaldehyde semicarbazone. When the ligands

were treated with cis-[RuCl2(DMSO)4)] in ethanol, all the ligands yielded

thiosemicarbazone complexes while the suspected semicarbazone ligand resulted in

orange-yellow crystalline product which has been found to be a semicarbazone

complex by XRD studies. A mechanism has been proposed for the conversion of

C=S to C=O during ligand preparation, which involves the role of adventitious

water in ethanol. All the complexes were characterized by analytical and

spectroscopic methods. The redox behaviors of the complexes were studied by

cyclic voltammetry. The preliminary DNA-binding ability of the complexes was

studied by recording electronic absorption spectra of the complexes in presence of

herring sperm DNA. Antibacterial activities of the complexes were also been

evaluated against five pathogenic bacteria.

Beckford et al.121

have synthesized a series of mixed ligand ruthenium(II)

complexes containing diimine as well as bidentate thiosemicarbazone ligands. The

compounds contain the diimine 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy)

and 9-anthraldehyde N(4)-substituted thiosemicarbazone (L). Based on elemental

analyses and spectroscopic data, the compounds were best formulated as

23

[(phen)2Ru(L)](PF6)2 and [(bpy)2Ru(L)](PF6)2. A fluorescence competition study

with ethidium bromide, along with viscometric measurements suggests that the

complexes bind calf thymus DNA (CT-DNA) relatively strongly via an

intercalative mode possibly involving the aromatic rings of the diimine ligands. The

complexes show good cytotoxic profiles against MCF-7 and MDA-MB-231 (breast

adenocarcinoma) as well as HCT-116 and HT-29 (colorectal carcinoma) cell lines.

Mohamed Subarkhan et al.122

have studied a new series of binuclear

ruthenium(III) complexes of general formula [(EPh3)2(X)2Ru-L-Ru(X)2(EPh3)2]

(E = P or As, X = Cl or Br, L = terepthaldehyde N(4)-substituted

thiosemicarbazones). IR spectra show that the thiosemicarbazones behave as

monoanionic bidentate ligands coordinating through the azomethine nitrogen and

thiolate sulfur. The electronic spectra of the complexes indicate that the presence of

d-d and intense LMCT transitions in the visible region. The complexes were

paramagnetic (low spin d5) in nature and all the complexes show rhombic distortion

around the ruthenium ion with three different ‘g’ values at 77K. The electrochemistry

of the complexes was studied by cyclic voltammetry. Further, the catalytic efficiency

of the complexes has been investigated in the case of oxidation of primary and

secondary alcohols into their corresponding aldehydes and ketones in the presence of

N-methylmorpholine-N-oxide (NMO) as co-oxidant. The formation of high valent

RuV=O species is proposed as catalytic intermediate for the catalytic cycle.

Upon reaction123

with Ru(PPh3)3Cl2 in ethanol in the presence of

triethylamine, acetone thiosemicarbazone undergoes several interesting chemical

transformations, such as thiolation via methyl C-H bond activation, C-N bond

cleavage and conversion of the C=S fragment to C=O. Two complexes were

obtained from this reaction, both of which contained a modified thiosemicarbazone

coordinated in SNS- or SNO-mode, two triphenylphosphines and N-bound

thiocyanate. The crystal structure of both the complexes has been determined.

Theoretical and mass spectral studies have been carried out to probe the

transformations. These complexes show intense absorptions in the visible and

ultraviolet regions. Cyclic voltammetry on both the complexes shows a reversible

oxidation near 0.6 V vs. SCE, followed by an irreversible oxidation near 1.2 V vs.

24

SCE. DFT calculations have been carried out to explain the electronic spectra as

well as the electrochemical observations.

Ruthenium(II) cyclometallated complex containing p-chloroacetophenone

thiosemicarbazone (L) of formula [Ru(L)(CO)(PPh3)2] has been reported by

Pandiarajan et al.124

The thiosemicarbazone ligand coordinates to ruthenium as a

terdentate C, N, and S donor generating two five membered metallacycles. The

crystal structure analysis of the complex [Ru(L)(CO)(PPh3)2] indicates presence of

a distorted octahedral geometry. Further, the catalytic transfer hydrogenation of

substituted acetophenones by the titled complex was carried out with conversions

up to 99.3% in the presence of i-prOH/KOH.

Mostafa et al.125

have studied the new ruthenium(II) complexes with

2-hydroxybenzophenone N-substituted thiosemicarbazones. The thiosemicarbazones

coordinate to ruthenium(II) as mononegative tridentate ligands via the deprotonated

hydroxyl group, azomethine nitrogen and thione sulfur centres. The redox properties,

nature of the electrode processes and the stability of the complexes towards oxidation

in CH2Cl2 were discussed. The change in the E1/2 values of the complexes can be

related to the basicity of the N(4)-substituents. All the complexes display an

irreversible one-electron charge-transfer couple in the potential range studied.

A new dissymmetric ruthenium(II) carbonyl complexes of the type

[Ru(CO)(EPh3)(L1-2)] (E = P or As; L1 = N(4)-(2-hydroxy-5-chlorobenzylidene)-2-

amino-5-chlorobenzophenone thiosemicarbazone and L2 = N(4)-(2-hydroxy

naphthalene-1-carbaldehyde)-2-amino-5-chlorobenzophenone thiosemicarbazone)

have been reported by Vijayan et al.126

The molecular structure of the

representative complexes have been analyzed by single crystal X-ray studies and

found that the ruthenium(II) complexes possess a distorted octahedral geometry.

The DNA binding studies such as emissive titration, ethidium bromide/methylene

blue (EB/MB) displacement assay and viscometry measurements revealed that the

ruthenium(II) complexes bound with calf thymus DNA through intercalative mode

with relatively high binding constant values. Further, the interactions of the

complexes with bovine serum albumin (BSA) were also investigated using

fluorescence spectroscopic methods, which showed that the new complexes could

25

bind strongly with BSA. The complexes were tested for DNA and BSA cleavage

activities and the results showed that the complexes exhibited good cleavage

properties. In addition, the newly synthesized ruthenium(II) complexes possess

better in vitro cytotoxic activities against various cell lines (MCF-7, Hop62, MDA-

MB-435) and AO/EB staining method showed that these complexes induced

apoptosis of MCF-7 cell lines.

Thilagavathi et al.127

have reported the synthesis and characterization of

new series of mixed ligand semicarbazone or thiosemicarbazone complexes of

ruthenium(II) having the general formula [RuCO(EPh3)(B)L] (E = P or As; B =

PPh3, AsPh3 or py; L = dibasic tridentate ligand derived by the condensation of

ethylacetoacetate/methylacetoacetate and thiosemicarbazide/semicarbazide). A

comparative study on the catalysis of oxidation of benzyl alcohol, cyclohexanol,

cinnamyl alcohol, n-butanol, n-propanol and iso-butyl alcohol has been done with

N-methylmorpholine-N-oxide and molecular oxygen as co-oxidants. Catalytic

activity studies of the complexes in coupling reactions have been carried out. The

antibacterial properties of the complexes have also been examined.

New ruthenium(II) carbonyl complexes of general formula

[Ru(L)(CO)(B)(EPh3)] (E = P or As, B = PPh3, AsPh3, py, pip or mor, L =

dehydroacetic acid thiosemicarbazone) have been reported by Kannan et al.128

The

thiosemicarbazone of dehydroacetic acid behaves as dianionic tridentate O, N, S

donor and coordinates to ruthenium via phenolic oxygen of dehydroacetic acid, the

imine nitrogen of thiosemicarbazone and thiol sulfur. In chloroform solution, all the

complexes exhibit metal-to-ligand charge transfer transitions (MLCT). The crystal

structure of representative complex has been determined by single crystal X-ray

diffraction which reveals the presence of a distorted octahedral geometry in the

complexes. All the complexes exhibit an irreversible oxidation (RuIII

/RuII) in the

range 0.76-0.89 V and an irreversible reduction (RuII/Ru

I) in the range -0.87 to -

0.97 V. Further, the free ligand and its ruthenium complexes have been screened for

their antibacterial and antifungal activities. The complexes show better activity in

inhibiting the growth of bacteria Staphylococcus aureus and Escherichia coli and

fungus Candida albicans and Aspergillus niger.

26

Ulaganatha Raja et al.129

reported the synthesis and characterization of

ruthenium(II) complexes of the type [Ru(L)(CO)(B)(EPh3)] (E =P or As, B = PPh3,

AsPh3, py or pip and L = dehydroacetic acid semicarbazone or dehydroacetic acid

phenyl thiosemicarbazone). The coordination mode of the ligands and the geometry

of the complexes were confirmed by single crystal X-ray crystallography. All the

complexes were redox active and were monitored by cyclic voltammetric

technique. Further, the catalytic efficiency of the complexes was determined in the

case of oxidation of primary and secondary alcohols into their corresponding

aldehydes and ketones in the presence of N-methylmorpholine-N-oxide.

Mononuclear ruthenium(III) complexes of the type [RuX(EPh3)2(L)] (E = P

or As, X= Cl or Br, L = dehydroacetic acid thiosemicarbazones) have been

synthesized from the reaction130

of thiosemicarbazone ligands with ruthenium(III)

precursors in benzene. The composition of the complexes has been established by

elemental analyses, magnetic susceptibility measurement, FT-IR, UV-Vis and EPR

spectral data. These complexes were paramagnetic and show intense d-d and charge

transfer transitions in dichloromethane. The complexes show rhombic EPR spectra

at liquid nitrogen temperature (LNT) which were typical of low-spin distorted

octahedral ruthenium(III) species. All the complexes were redox active and display

an irreversible metal centered redox processes. Complexes were used as catalyst for

transfer hydrogenation of ketones in the presence of isopropanol/KOH and were

found to be the active species.

Ruthenium(II) complexes with 2-acetylpyridine thiosemicarbazones were

synthesized131

and characterized by analytical and spectral (FT-IR, UV-Vis, NMR,

ESI-Mass) methods. Systematic biological investigations, free radical scavenging,

anticancer activities and DNA cleavage studies were carried out for the complexes.

Antioxidant studies showed that the complexes have significant antioxidant activity

against DPPH, hydroxyl, nitric oxide radicals and hydrogen peroxide assay. The in

vitro cytotoxicity of complexes against breast cancer (MCF-7) cell line was assayed

showing high cytotoxicity with low IC50 values indicating their efficiency in

destroying the cancer cells even at very low concentrations. The DNA cleavage

studies showed that the complexes efficiently cleaved DNA.

27

Two ruthenium(II) complexes of 2-acetylpyridine N(4)-

dimethylthiosemicarbazone (HL1) and phenanthrenequinone thiosemicarbazone

(HL2) namely [RuCl(L1)(PPh3)2] and [RuCl(L2)(PPh3)2] have been synthesized by

Grguric-Sipka et al.132

In addition, the X-ray crystal structure of [RuCl2(L2)PPh3].

DMSO.1.25H2O was reported. The reaction of [RuCl2(DMSO)4] with HL1 and

1,3,5-triaza-7-phosphaadamantane (PTA) gives highly water-soluble complex

[RuCl(L1)(HPTA)2]Cl2.C2H5OH.H2O, which has been fully characterized. The

complexes showed a strong antiproliferative effects in low micromolar

concentrations in the ovarian carcinoma cell line 41M (IC50 = 0.87 μM) and more

moderate activity in the breast cancer cell line SK-BR-3 (IC50 = 39 μM).

Manikandan et al.133

have reported the synthesis and characterization of

ruthenium(III) Schiff base complexes containing 2-acetylpyridine

thiosemicarbazone/semicarbazone. The new complexes were found to be efficient

catalyst for transfer hydrogenation and Kumada-Corriu coupling reactions. The

complexes also successfully cleaved the DNA.

Ruthenium(II) complexes containing mono(4-(4-tolyl)thiosemicarbazone)

of 2,6-diacetylpyridine (HL1) synthesized by using three different ruthenium-

containing starting materials RuCl3.3H2O, Ru(PPh3)3Cl2 and [Ru(NH3)5Cl]Cl2 were

reported.134

The structure of the compound [Ru(L1)(PPh3)2]ClO4 has been

determined by single-crystal X-ray diffraction technique. The deprotonated ligand

was chelated to the ruthenium(II) center through the oxygen of the carbonyl group,

pyridine ring nitrogen, imine nitrogen and the thiolate sulfur atoms. Strong

coordination of the carbonyl group has been confirmed from the appreciable

shortening of the Ru-O bond and lengthening of the C=O bond from IR spectral

data.

Complexes of the type [RuCl2(DMSO)2L] (L = 5-nitrofurylsemicarbazone

derivatives) were reported by Cabrera et al.135

The new complexes were excellent

DNA binding agents for calf thymus DNA. So, their in vitro anti-tumor activity was

tested in cellular models and the complexes were found to be non-cytotoxic on the

tumor cell lines assayed, neither in aerobic conditions nor in the bio-reductive assay

performed. Redox behavior, lipophilicity and stability were studied in order to

28

explain the lack of cellular cytotoxic effects. The complexes resulted 10-100 times

more hydrophilic than the parent ligands, thus the bio-activity of these compounds

would be compromised by their inadequate lipophilic properties.

A series of new hexa-coordinated ruthenium(II) hydroxyquinoline N(4)-

substituted thiosemicarbazone complexes of the type [Ru(CO)(EPh3)(B)(L)] (E = P

or As; B = PPh3, AsPh3 or py) were reported by Nirmala et al.136

The new

complexes were characterized by analytical and spectroscopic (FT-IR, UV-Vis,

NMR) and FAB-Mass spectrometric methods. Based on the spectral results, an

octahedral geometry was assigned for all the complexes. The new complexes

showed good catalytic activity for the conversion of aldehydes to amides in the

presence of hydroxylamine hydrochloride-sodium bicarbonate and for the oxidation

of alkanes into their corresponding alcohols and ketones in the presence of m-

chloroperbenzoic acid. The complexes also catalyzed the N-alkylation of

benzylamine in the presence of t-BuOK in alcohol medium.

A series of ruthenium(II) complexes of potentially NNS tridentate but

functionally NS bidentate chelating ligands in the form of 4-substituted 4-phenyl

and 4-cyclohexyl thiosemicarbazones of pyridine 2-aldehyde and thiophene

2-aldehyde have been synthesized137

using [Ru(PPh3)3Cl2] as the starting material.

All the complexes were characterized by elemental analyses, measurement of

conductance in solution, magnetic susceptibility at room temperature and

spectroscopic techniques. Electrochemical behavior of the complexes has been

examined by cyclic voltammetry. Structure of representative complexes has been

solved by single crystal X-ray diffraction technique. All the ligands were found to

be chelated to the ruthenium(II) center in its thione form through its imine nitrogen

and the thione sulfur. The pyridine ring nitrogen remained uncoordinated. The two

PPh3 molecules are situated cis to each other. All the complexes were found to

exhibit biological activity in terms of Escherichia coli growth-inhibition capacity

and two of them hold the possibility of displaying antitumor activity.

The synthesis and characterization of a number of organometallic

ruthenium(II) complexes containing a series of bidentate thiosemicarbazone ligands

derived from piperonal was reported by Beckford et al.138

The structure of

29

compounds has been confirmed by spectroscopic analysis (IR and NMR) as well as

X-ray crystallographic analysis. The interaction of the complexes with calf thymus

DNA, human serum albumin (HSA) and pBR322 plasmid DNA were studied by

spectroscopic, gel electrophoresis and hydrodynamic methods. The in vitro

anticancer activity of complexes has been evaluated against two human colon

cancer cell line (HCT-116 and Caco-2) with IC50 values in the range of 26-150 μM.

Complexes show good activity as a catalytic inhibitor of human topoisomerase II at

concentrations as low as 20 μM. The proficiency of complexes to act as

antibacterial agents was also evaluated against six pathogenic bacterial strains with

the best activity seen against Gram-positive strains.

Ramachandran et al.139

have described the synthesis, characterization and

catalytic activity of ruthenium(II) carbonyl complexes [RuCl(CO)(EPh3)(L)] with

PNS type thiosemicarbazone ligands (E = P or As, L = 2-(2-(diphenylphosphino)

benzylidene) N(4)-substituted thiosemicarbazone). The molecular structure of

complexes was identified by means of single-crystal X-ray diffraction analysis. The

analysis revealed that all the complexes possess a distorted octahedral geometry

with the ligand coordinating in a uni-negative tridentate PNS fashion. The

complexes were tested as catalyst for N-alkylation of heteroaromatic amines with

alcohols and results show that complexes was found to be efficient and versatile

catalysts towards N-alkylation of a wide range of heterocyclic amines with

alcohols. Complexes can also catalyze the direct amination of 2-nitropyridine with

benzyl alcohol to the corresponding secondary amine. Furthermore, a preliminary

examination of performance for N,N-dialkylation of diamine showed promising

results, giving good conversion and high selectivity. In addition, N-alkylation of

o-substituted anilines (–NH2, –OH and –SH) led to the one-pot synthesis of 2-aryl

substituted benzimidazoles, benzoxazoles and benzothiazoles also revealing the

catalytic activity of complexes.

A series of ruthenium(II) complexes [(diimine)2Ru(L)](PF6)2 (L =

thiosemicarbazone ligands derived from benzo[d][1,3]dioxole-5-carbaldehyde)

have been synthesized by Beckford et al.140

The diimine in the complexes is either

2,2′-bipyridine or 1,10-phenanthroline. The complexes have been characterized by

30

spectroscopic methods as well as by elemental analyses. The biophysical

characteristics of the complexes were studied by investigating their anti-oxidant

ability as well as their ability to disrupt the function of the human topoisomerase II

enzyme. The complexes were moderately strong binders of DNA with binding

constants of 104

M-1

. They were also strong binders of human serum albumin

having binding constants in the order of 104

M-1

. The complexes show good in vitro

anticancer activity against human colon cancer cells, Caco-2 and HCT-116. They

also have antibacterial activity against Gram-positive and Gram-negative strains.

All the compounds were catalytic inhibitors of human topoisomerase II.

Tameryn Stringer et al.141

reported a series of mono- and dinuclear

(η6-arene) ruthenium(II) complexes and they were prepared by reaction of

thiosemicarbazone ligands derived from benzaldehyde and ruthenium(II) precursors

of the general formula [Ru(η6-arene)(μ-Cl)Cl]2, where arene = p-

iPrC6H4Me or

C6H5C3H6COOH. These complexes were characterized by NMR and IR

spectroscopy, ESI-mass spectrometry and elemental analyses. The molecular

structure of the mononuclear p-cymene complex was determined by X-ray

diffraction analysis, revealing a pseudo tetrahedral piano stool conformation and a

bidentate N,S coordination mode of the thiosemicarbazone ligand. The complexes

and ligands were evaluated for their in vitro cytotoxicity against the WHCO1

oesophageal cancer cell line.

An organometallic salt composed of a new cationic p-cymene ruthenium

chloro complex containing a chelating benzaldehyde semicarbazone ligand and of

the known anionic p-cymene ruthenium trichloro complex, [(η6-p-cymene)

Ru(bzsc)Cl]+[(η

6-p-cymene)RuCl3]

– (bzsc = benzaldehyde semicarbazone) was

synthesized142

and further characterized by IR, 1H NMR and UV-Vis spectroscopy,

HR-ESI mass spectrometry and elemental analyses. The single-crystal structure of

complex was also determined. The in vitro anticancer activity of the complex was

evaluated against three human cancer cell lines (SGC-7901, BEL-7404 and CNE-1)

and the IC50 values were 20.7, 71.1 and 42.6 μM respectively.

Su et al.143

have reported the synthesis and spectral characterization of

half-sandwich ruthenium(II) arene complexes [(η6-p-cymene)Ru(L)Cl]Cl

31

(L = benzaldehyde N(4)-substituted thiosemicarbazones). The single-crystal

structure of complexes has also been determined. The molecular orbitals and

electronic absorption spectra of the complexes have been calculated using the DFT

and TDDFT methods. The in vitro antiproliferative activities of these complexes

have been evaluated against four human cancer cell lines (CNE, H292, SKBR3 and

Hey1-B) and the complexes was proved to be the most efficient inhibitor.

The interaction144

between [(η6-p-cymene)Ru(benzaldehyde-N(4)-

phenylthiosemi carbazone)(Cl]Cl anticancer drug and human serum albumin (HSA)

was investigated systematically under physiological conditions by using some

spectroscopic methods (UV-Vis, fluorescence, FT-IR, CD and mass spectroscopy)

and cyclic voltammetry. The experimental results indicate that this anticancer drug

could quench the intrinsic fluorescence of HSA through static quenching

mechanism. The Stern-Volmer quenching model has been successfully applied and

the Stern-Volmer quenching constants together with the modified Stern-Volmer

quenching constants at different temperatures were also calculated. The

corresponding thermodynamic parameters DH, DG and DS were also calculated.

The binding of this anticancer drug and HSA resulted in the formation of drug-HSA

complex and the electrostatic interaction played a major role in the complex

stabilization. The distance r between the donor (HSA) and the acceptor (drug) was

obtained through fluorescence resonance energy transfer theory. Competitive

experiments indicated that the binding site of this anticancer drug to HSA was

located at site I. The results of synchronous fluorescence spectra, three-dimensional

fluorescence spectra, FT-IR spectra and CD spectra indicated that the

microenvironment and the conformation of HSA were changed noticeably due to

the presence of this anticancer drug. The results of mass spectra and cyclic

voltammetry further confirmed the interaction between HSA and this anticancer

drug. These results indicated that the biological activity of HSA was dramatically

affected by the anticancer drug.

Cationic half-sandwich arene ruthenium(II) complexes of general formula

[Ru(η6-p-cymene)Cl(L)]Cl have been synthesized by Ulaganatha Raja et al.

145 from

the reaction of [Ru(η6-p-cymene)Cl2]2 with thiosemicarbazone derivatives (L).

32

Characterization of the complexes were accomplished by analytical and spectral

(FT-IR, UV-Vis, 1H NMR) methods. Single crystal structure determination reveals

the presence of a pseudo octahedral three-legged piano stool conformation. All the

complexes exhibit a quasi-reversible one electron reduction in the range from -0.75

to -0.85 V. Further, the catalytic activity of the complexes has been investigated in

the transfer hydrogenation of ketones in the presence of isopropanol/NaOH.

A series of half-sandwich arene ruthenium complexes containing bidentate

thiosemicarbazone ligands have been synthesized146

and their biological activity

was investigated. The compounds have the general formula [(η6-p-

cymene)Ru(L)Cl]X (L = 9-anthraldehyde η6-p-cymene thiosemicarbazone and X =

Cl, PF6). The crystal structure of representative complex has been determined and

represents the first structurally characterized arene-ruthenium half-sandwich

complex with a thiosemicarbazone ligand. The complexes show good cytotoxic

profiles against MCF-7 and MDA-MB-231 (breast adenocarcinoma) as well as

HCT-116 and HT-29 (colorectal carcinoma) cell lines.

A series of ketone-N(4)-substituted thiosemicarbazone (L) compounds and

their corresponding [(η6-p-cymene)Ru(L)Cl]

+/0 complexes were synthesized

147 and

characterized by NMR, IR, elemental analyses and HR-ESI-mass spectrometry. The

compounds were further evaluated for their in vitro antiproliferative activities

against the SGC-7901 human gastric cancer, BEL-7404 human liver cancer and

HEK-293T noncancerous cell lines. Furthermore, the interactions of the compounds

with DNA were followed by electrophoretic mobility spectrometry studies.

Rhodium complexes

The reactions of 4(R)-benzaldehyde thiosemicarbazones (R = OCH3, CH3,

H, Cl and NO2) with [Rh(PPh3)3Cl] in refluxing ethanol in the presence of a base

have been reported by Acharyya et al.148

A group of organorhodium complexes

were obtained from such reactions, in which the oxidized thiosemicarbazones were

coordinated to rhodium as tridentate CNS donors, along with two

triphenylphosphines and a hydride. From the reaction with p-nitrobenzaldehyde

thiosemicarbazone, a second organometallic complex was obtained, in which the

33

thiosemicarbazone was coordinated to rhodium as a tridentate CNS donor, along

with two triphenylphosphines and a hydride. Reaction of the benzaldehyde

thiosemicarbazones with [Rh(PPh3)3Cl] in refluxing ethanol in the absence of base

affords another group of organorhodium complexes, in which the

thiosemicarbazones were coordinated to rhodium as tridentate CNS donors, along

with two triphenylphosphines and a chloride. Structure of representative complexes

of each type of complexes has been determined by X-ray crystallography. In all of

the complexes, the two PPh3 ligands were trans to each other. All of the complexes

show intense MLCT transitions in the visible region. Cyclic voltammetry on these

complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE. Redox

responses of the coordinated thiosemicarbazones were also displayed by all of the

complexes.

p-Nitrobenzaldehyde semicarbazone undergoes an unusual chemical

transformation upon reaction149

with [Rh(PPh3)3Cl] in the presence of trialkyl and

dialkylamines via dissociation of the C-NH2 bond and formation of a new C-NR2

bond (where the NR2 fragment was provided by the amine). The transformed

semicarbazone ligand binds to rhodium as a dianionic C,N,O-donor to afford the

complexes. Another group of semicarbazones (viz. salicylaldehyde semicarbazone,

2-hydroxyacetophenone semicarbazone and 2-hydroxynaphthaldehyde

semicarbazone) has also been observed to undergo a similar chemical

transformation upon reaction with [Rh(PPh3)3Cl] under similar experimental

conditions and these transformed semicarbazones bind to rhodium as dianionic

O,N,O-donors affording the complexes. The structure of the representative

complexes has been determined. All the complexes show characteristic 1H NMR

signals. They also show intense absorptions in the visible and ultraviolet region.

Kumar Seth et al.150

have reported the reaction of 4(R)-benzaldehyde

thiosemicarbazones (R = OCH3, CH3, H, Cl, NO2) with [Rh(PPh3)3Cl] in refluxing

ethanol in the presence of a base (NEt3). It afforded the organorhodium complexes

(1-R) in which the thiosemicarbazones were coordinated to rhodium as tridentate

CNS donors with the sulfur atom oxidized by aerial oxygen to sulfone. Two

triphenylphosphines and a hydride were also coordinated to the metal center. From

34

the reaction with 4-nitrobenzaldehyde thiosemicarbazone, a second organorhodium

complex (2-NO2) was obtained, in which the sulfur atom was not oxidized.

Reaction of the 4(R)-benzaldehyde thiosemicarbazones with [Rh(PPh3)3Cl] in

refluxing ethanol in the absence of NEt3 affords another group of organorhodium

complexes (3-R) in which the thiosemicarbazones were coordinated to rhodium as

tridentate CNS donors, along with two triphenylphosphines and a chloride. In these

complexes also the sulfur atom is not oxidized. Structures of all the complexes have

been optimized by DFT calculations and compared with the already known X-ray

crystallographic structures. Also the experimentally observed electronic absorption

bands have been assigned to specific transitions based on the TDDFT studies.

Molecular electrostatic potential (MESP) topographical analysis performed to find

the deepest MESP point on the coordinated sulfur atom (Vmin) was used as a probe

for assessing the oxidizability of the coordinated sulfur in 2-R and 3-R complexes.

Energy differences between the three sets of complexes have been estimated and

based on the results obtained 3-R has been experimentally transformed into 1-R via

formation of 2-R as the intermediate.

Interaction of the cis-[Rh(PR3)2(solv)2]PF6 complexes (R = Ar or Ph2Me,

solv-Me2CO, MeOH) under argon with semicarbazones bearing a phenyl group on

the imine-C atom gives the rhodium(III)-hydrido-bis(phosphine)-orthometallated

semicarbazone species [RhH(PR3)2(o-C6H4(R′)C=NN(H)CONH2)]PF6 (R′ = Me or

Et) was reported by Ezhova et al.151

The structure of PPh3 containing complex with

R′ = Me was characterized by X-ray analysis, reveals coordination of the

semicarbazone by the ortho-C atom, the imine-N atom and the amide-carbonyl

group. For a semicarbazone containing no Ph group, the rhodium(I) complex

[Rh(PR3)2(Et(Me)C=N-N(H)CONH2)]PF6 containing the semicarbazone bonded

via the imine-N and carbonyl group. Attempts to hydrogenate the C=N moiety in

the complexes or to catalytically hydrogenate the semicarbazones were

unsuccessful.

Interaction152

of cis,trans,cis-[Rh(H)2(PR3)2(acetone)2]PF6 complexes (R =

aryl or Ph2Me, Ph2Et) under H2 with E-semicarbazones gives the Rh(III)-dihydrido-

bis(phosphine)-semicarbazone species cis,trans-[Rh(H)2(PR3)2(R′(R′′)C=NN(H)CO

35

NH2)]PF6, where R′ and R′′ are Ph, Et or Me. The complexes were generally

characterized by elemental analyses and spectroscopic methods. X-ray analysis of

PPh3 containing complexes reveals chelation of E-semicarbazones by the imine-N

atom and the carbonyl-O atom. In contrast, the corresponding reaction of

[Rh(H)2(PPhMe2)2(acetone)2]PF6 with acetophenone semicarbazone gives the

orthometalated-semicarbazone species cis-[RhH(PPhMe2)2(o-C6H4(Me)C=N-N(H)

CONH2)]PF6. Rhodium catalyzed homogeneous hydrogenation of semicarbazones

was not observed even at 40 atm H2.

The synthetic, spectroscopic, and biological studies of ring-substituted

4-phenyl/4-nitrophenylthiosemicarbazones of anisaldehyde, 4-chloro/

4-fluorobenzaldehyde and vanillin with ruthenium(III) and rhodium(III) chlorides

were reported by Sharma et al.153

Their structure was determined on the basis of the

elemental analyses, spectroscopic data (IR, UV-Vis, NMR) along with magnetic

susceptibility measurements, molar conductivity and thermogravimetric analyses.

Electrical conductance measurement revealed a 1:3 electrolytic nature of the

complexes. The resulting colored products were monomeric in nature. On the basis

of the above studies, the ligands were suggested to be coordinated to each metal

atom by thione sulfur and azomethine nitrogen to form low-spin octahedral

complexes. Both ligands and their complexes have been screened for their

bactericidal activities and the results indicate that they exhibit a significant activity.

Reaction of salicylaldehyde/2-hydroxyacetophenone/2-hydroxy

naphthaldehyde thiosemicarbazone (L) with [Rh(PPh3)3Cl] was reported by Dutta et

al.154

and afforded a family of rhodium(III) complexes of the type

[Rh(PPh3)2(L)Cl]. The crystal structure of representative complex has been

determined by X-ray diffraction. The thiosemicarbazone ligands were coordinated

via dissociation of the two protons, as dianionic tridentate O,N,S-donor ligands

forming one six-membered and one five-membered chelate rings. The complexes

were diamagnetic (low-spin d6, S = 0) and their

1H NMR spectra were in excellent

agreement with their compositions. All three [Rh(PPh3)2(L)Cl] complexes display

intense absorptions in the visible and ultraviolet regions. They also show strong

emission in the visible region at ambient temperature.

36

Mukkanti et al.155

have synthesized the complexes of thiophene-2-

carboxaldehyde thiosemicarbazone with RuIII

, RhIII

, IrIII

and PtIV

. All the complexes

were characterized by elemental analyses, molar conductance, magnetic moments,

infrared and electronic spectral studies. Probable structure for the complexes was

suggested. All were diamagnetic except the RuIII

octahedral complexes. The crystal

field parameters of the complexes have also been calculated.

The chelating behavior of two biologically active ligands, pyridine-2-

carboxaldehyde thiosemicarbazone/4-phenyl thiosemicarbazone towards FeIII

, CoIII

,

FeII

and RhIII

has been investigated by Chattopadhyay et al.156

The ligands act as

tridentate NNS donors, resulting in the formation of bis-chelate complexes.

Biological activity of the ligands and the metal complexes in the form of in vitro

antibacterial activities towards E. coli has been evaluated and the possible reason

for enhancement of the activity of ligands on coordination to metal ion was

discussed.

Muthusamy et al.157

have synthesized several new hexa-coordinated

ruthenium(II) and penta-coordinated rhodium(I) complexes containing

thiosemicarbazones of 2-furaldehyde/thiophene-2-carboxaldehyde/p-anisaldehyde/

piperonaldehyde/cyclohexanone. All the new complexes have been characterized

on the basis of elemental analyses, IR, UV-Vis and NMR spectral data.

The thiosemicarbazones of anisaldehyde/3,4-dimethoxybenzaldehyde/

thiophene-2-aldehyde/2-acetylpyridine/acetylacetone and their complexes with

palladium, ruthenium and rhodium have been synthesized158

and characterized by

elemental analyses, electrical conductance, magnetic susceptibility, IR and UV-Vis

studies. Both the ligands and their complexes have been screened for their

fungicidal and bactericidal activities. The results indicate that they exhibit

significant antimicrobial properties.

Jain et al.159

have isolated the ruthenium(III) and rhodium(III) complexes

from the reaction of α-pyridyl thiosemicarbazide/l-benzilidine 4-(α-pyridyl)

thiosemicarbazone with metal(III) chlorides. The obtained complexes characterized

37

by elemental analyses, conductance, magnetic, UV-Vis and IR studies in order to

evaluate the stereochemistry of the ligand around the metal ions.

Singh et al.160

have synthesized rhodium(III) complexes of semicarbazones

derived from 4-aminoantipyrine and various aryl aldehydes. The complexes were

characterized by elemental analyses, magnetic moments, IR and UV-Vis spectral

studies. The complexes were found to have the composition [Rh(L)Cl3]. All the

complexes were octahedral and diamagnetic.

The ligation behavior of bis-benzoin ethylenediamine and benzoin

thiosemicarbazone Schiff bases towards Ru3+

, Rh3+

, Pd2+

, Ni2+

and Cu2+

were

investigated by El-Shahawi et al.161

The bond length and spectrochemical

parameters (10Dq, β, B and LFSE) of the complexes were evaluated. The redox

characteristics of selected complexes were explored by cyclic voltammetry (CV) at

Pt working electrode in non aqueous solvents. Au mesh optically transparent thin

layer electrode was also used for recording thin layer CV for selected Ru complex.

The characteristics of electron transfer process of the couples M2+

/M3+

and M3+

/M4+

(M = Ru3+

, Rh3+

) and the stability of the complexes towards oxidation and

reduction were assigned. The nature of the electroactive species and reduction

mechanism of selected electrode couples were assigned.

From the above discussion it was found that nickel, ruthenium and

rhodium complexes of thiosemicarbazone/semicarbazone exhibited variety

of coordination modes and interesting biological and catalytic activities. However,

no work has been found which deal with biological activities of ruthenium

complexes containing quinone based thiosemicarbazone/semicarbazone

ligands. Hence, it was worthwhile to synthesize ruthenium(II/III) complexes

containing 9,10-phenanthrenequinone/1,2-naphthaquinone appended with

thiosemicarbazone/semicarbazone and study their biological activities. In addition,

among the various transition metals, nickel, ruthenium and rhodium complexes

have a long heredity of catalytic applications. So, some important catalytic organic

conversions using the nickel(II), ruthenium(II) and rhodium(I) 9,10-

phenanthrenequinone thiosemicarbazone complexes as catalysts were studied.

38

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