CHAPTER I Introduction - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/60345/6/06_chapter...
Transcript of CHAPTER I Introduction - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/60345/6/06_chapter...
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
References
1. N. Hoshimo, Coord. Chem. Rev. 174 (1998) 77-108.
2. L. Zhao, Q. Hou, D. Sui, Y. Wang, S. Jiang, Spectrochim. Acta A 67 (2007)
1120-1125.
3. S. Wang, G. Men, L. Zhao, Q. Hou, S. Jiang, Sensor Actuator. B Chem. 145
(2010) 826-831.
4. K. Das, N. Sarkar, A.K. Ghosh, D. Majumadar, D.N. Nath, K. Bhattacharya,
J. Phys. Chem. 98 (1994) 9126-9132.
5. M. Fores, M. Duran, M. Sola, J. Phys. Chem. 103 A (1999) 4525-4528.
6. A.U. Acuna, F.A. Guerri, A. Costela, A. Douhal, J.M. Figuera, F. Florido,
R. Sastre, Chem. Phys. Lett. 187 (1991) 98-102.
7. M.J. Climent, A. Corma, S. Iborra, Chem. Rev. 111 (2011) 1072-1133.
8. G. Evano, N. Blanchard, M. Toumi, Chem. Rev. 108 (2008) 3054-3131.
9. M.J.M. Campbell, Coord. Chem. Rev. 15 (1975) 279-319.
10. S. Padhye, G.B. Kauffman, Coord. Chem. Rev. 63 (1985) 127-160.
11. J.S. Casas, M.S. Garcia-Tasende, J. Sordo, Coord. Chem. Rev. 209 (2000)
197-261.
12. a. S. Patai (Ed.), The Chemistry of the Quinoid Compounds, Parts 1 and 2,
Wiley, New York, 1974.
b. R.H. Thompson, Naturally Occurring Quinones, 2nd
edn. Academic Press,
New York, 1971.
c. S.V. Khan, Humic Substances in the Environment, Dekker, New
York, 1972.
13. a. C.G. Pierpont, R.M. Buchanan, Coord. Chem. Rev. 38 (1981) 45-87.
b. A. Vlcek Jr, Comments Inorg. Chem. 16 (1994) 207-228.
c. C.G. Pierpont, Coord. Chem. Rev. 219-221 (2001) 415-433.
d. D.A. Shultz, Comments Inorg. Chem. 23 (2002) 1-21.
e. P. Zanello, M. Corsini, Coord. Chem. Rev. 250 (2006) 2000-2022.
f. O. Sato, J. Tao, Angew. Chem. Int. Ed. 46 (2007) 2152-2187.
g. A.I. Poddelsky, V.K. Cherkasov, G.A. Abakumov, Coord. Chem. Rev. 253
(2009) 291-324.
h. A.V. Piskunov, A.I. Poddelsky, Global J. Inorg. Chem. 2 (2011) 110-149.
39
14. a. C.G. Pierpont, Coord. Chem. Rev. 216-217 (2001) 99-125.
b. V.K. Cherkasov, G.A. Abakumov, E.V. Grunova, A.I. Poddelsky,
G.K. Fukin, E.V. Baranov, Yu.A. Kurskii, L.G. Abakumova, Chem. Eur. J.
12 (2006) 3916-3927.
c. E.V. Ilyakina, A.I. Poddel'sky, V.K. Cherkasov, G.A. Abakumov,
Mendeleev Commun. 22 (2012) 208-210.
15. R.M. Buchanan, C. Wilson-Blumenberg, C. Trapp, S.K. Larsen, D.L.
Greene, C.G. Pierpont, Inorg. Chem. 25 (1986) 3070-3076.
16. S.A. Kretchmar, K.N. Raymond, J. Am. Chem. Soc. 108 (1986) 6212-6218.
17. G. Powis, M.P. Hacker, The Toxicity of Anticancer Drugs, Pergamon Press,
1991.
18. M.G. Miller, A. Rodgers, G.M. Cohen, Biochem. Pharmacol. 35 (1986)
1177-1184.
19. P. Neta, The Chemistry of Quinonoid Compounds, S. Patai, Z. Rappoport
(Eds.), Wiley, New York, 1989.
20. H. Kappus, Biochem. Pharmacol. 35 (1986) 1-6.
21. T.W. Gant, D.N.R. Rao, R.P. Mason, G.M. Cohen, Chem. Biol. Interact. 65
(1988) 157-173.
22. J.N. Lopes, F.S. Cruz, R. Docampo, Ann. Trop. Med. Parasit. 72 (1978) 523-
531.
23. C.J. Li, L.J. Zhang, B.J. Dezubw, C.S. Crumpacker, A.B. Pardee, Proc. Natl.
Acad. Sci. USA 90 (1993) 1839-1842.
24. C.J. Li, C. Wang, A.B. Pardee, Cancer Res. 55 (1955) 3712-3715.
25. S.M. Planchon, S. Wuerzberger, B. Frydman, Cancer Res. 55 (1995) 3706-
3711.
26. C.J. Li, I. Averboukh, A.B. Pardee, J. Biol. Chem. 268 (1993) 22463-22468.
27. D.A. Boothman, D.K. Trask, A.B. Pardee, Cancer Res. 49 (1989) 605-612.
28. L. Flowers-Geary, W. Bleczinki, R.G. Harvey, T.M. Penning, Chem. Biol.
Interact. 99 (1996) 55-72.
29. A. Kovacs, A. Vasas, J. Hohmann, Phytochemistry 69 (2008) 1084-1110.
30. H.W. Yoo, M.E. Suh, S.W. Park, J. Med. Chem. 41 (1998) 4716-4722.
40
31. W. Saenger, Principles of Nucleic Acid Structure, Springer, New York, 1983.
32. a. Z. Afrasiabi, E. Sinn, W. Lin, Y. Ma, C. Campana, S. Padhye, J. Inorg.
Biochem. 99 (2005) 1526-1531.
b. Z. Afrasiabi, E. Sinn, J. Chen, Y. Ma, A.L. Rheingold, L.N. Zakharov,
N. Rath, S. Padhye, Inorg. Chim. Acta 357 (2004) 271-278.
c. Z. Afrasiabi, E. Sinn, S. Padhye, S. Dutta , S. Padhye, C. Newton,
C.E. Anson, A.K. Powell, J. Inorg. Biochem. 95 (2003) 306-314.
d. J. Chen, Y. Huang, G. Liu, Z. Afrasiabi, E. Sinn, S. Padhye, Y. Ma,
Toxicol. Appl. Pharmacol. 197 (2004) 40-48.
e. Z. Afrasiabi, E. Sinn, P.P. Kulkarni, V. Ambike, S. Padhye,
D. Deobagakar, M. Heron, C. Gabbutt, C.E. Anson, A.K. Powell, Inorg.
Chim. Acta 358 (2005) 2023-2030.
f . S. Padhye, Z. Afrasiabi, E. Sinn, J. Fok, K. Mehta, N. Rath, Inorg. Chem.
44 (2005) 1154-1156.
g. C. Querci, R. D’Aloisio, R. Bortolo, M. Ricci, D. Bianchi, J. Mol. Catal. A
176 (2001) 95-100.
h. H. Klein, E. Auer, A. Dal, U. Lemke, M. Lemke, T. Jung,
C. Rohr, U. Florke, H. Haupt, Inorg. Chim. Acta 287 (1999) 167-172.
i . S. Dutta, S. Peng, S. Bhattacharya, Inorg. Chem. 39 (2000) 2231- 2234.
33. C. Orvig, M.J. Abrams, Chem. Rev. 99 (1999) 2201-2203.
34. H.R. Park, A. Tomida, S. Sato, Y. Tsukumo, J. Yun, T. Yamori,
Y. Hayakawa, T. Tsuruo, K. Shin-ya, J. Nat. Cancer Inst. 96 (2004) 1300-
1310.
35. H.M. Pineto, J.H. Schornagel (ed.), Platinum and Other Metal Coordination
Compounds in Cancer Chemotherapy, Plenum, New York, 1996.
36. P.C. Bruijnincx, P.J. Sadler, Curr. Opin. Chem. Biol. 12 (2008) 197-206.
37. C.M. Che, J.Sh. Huang, Coord. Chem. Rev. 231 (2002) 151-164.
38. G. Sava, I. Capozzi, A. Bergamo, R. Gagliardi, M. Cocchietto, L. Masiero,
M. Onisto, E. Alessio, G. Mestroni, S. Garbisa, Int. J. Cancer 68 (1996) 60-
66.
39. M. Galanski, V.B. Arion, M.A. Jakupec, B.K. Keppler, Curr. Pharm. Des. 9
(2003) 2078-2089.
41
40. Y.K. Yan, M. Melchart, A. Habtemariam, P.J. Sadler, Chem. Commun.
(2005) 4764-4776.
41. W.H. Ang, P.J. Dyson, Eur. J. Inorg. Chem. 20 (2006) 4003-4018.
42. V. Mahalingam, N. Chitrapriya, F.R. Fronczek, K.Natarajan, Polyhedron 27
(2008) 2743-2750.
43. S. Sharma, S.K. Singh, M. Chandra, D.S. Pandey, J. Inorg. Biochem. 99
(2005) 458-466.
44. C. Metcalfe, J.A. Thomas, Chem.Soc. Rev. 32 (2003) 215-224.
45. L. Canali, D.C. Sherrington, Chem. Soc. Rev. 28 (1999) 85-93.
46. V.C. Gibson, S.K.Spitzmesser, Chem. Rev. 103 (2003) 283-315.
47. S.N. Rao, N. Kathale, N.N. Rao, K.N. Munshi, Inorg. Chim. Acta 360 (2007)
4010-4016.
48. S. Jammi, P. Saha, S. Sanyashi, S. Sakthivel, T. Punniyamurthy, Tetrahedron
64 (2008) 11724-11731.
49. I. Iwakura, T. Ikeno, T. Yamada, Org. Lett. 6 (2004) 949-952.
50. D.A. Atwood, M.J. Harvey, Chem. Rev. 101 (2001) 37-52.
51. S. Yamada, Coord. Chem. Rev. 190-192 (1999) 537-555.
52. C.M. Che, J.S. Huang, Coord. Chem. Rev. 242 (2003) 97-113.
53. J. Hassan, M. Sevignon, C. Gozzi, E. Schulz, M. Lemaire, Chem. Rev. 102
(2002) 1359-1469.
54. S.I. Murahashi (Ed.), Ruthenium in Organic Synthesis, Wiley-VCH,
Weinheim, 2004.
55. C. Bruneau, P.H. Dixneuf (Eds.), Ruthenium Catalysts and Fine Chemistry,
Springer, Berlin, 2004.
56. W.P. Griffith, Ruthenium Oxidation Complexes: Their Uses as Homogeneous
Organic Catalysts, Springer, Dordrecht, 2011.
57. W.A. Herrmann, B. Cornils, Applied Homogeneous Catalysis with
Organometallic Compounds, VCH Weinheim, 1999.
58. G.W. Parshall, S.D. Ittel, Homogeneous Catalysis, 2nd
edn, Wiley-
Interscience, New York, 1992.
59. K. Weissermel, H.J. Arpe, Industrial Organic Chemistry, 3rd
edn, VCH,
Weinheim, 1997.
42
60. H.M. Colquhoun, D.J. Thompson, M.V. Twigg, Carbonylation: Direct
Synthesis of Carbonyl Compounds, Plenum Press, New York, 1991.
61. a. K. Tamao, K. Sumitani, M. Kumada, J. Am. Chem. Soc. 94 (1972) 4374-
4376.
b. R.J.P. Corriu, J.P. Masse, J. Chem. Soc. Chem. Commun. (1972) 144a-
144a.
62. a. I. Paterson, R.D.M. Davies, R. Marquez, Angew. Chem. Int. Ed. 40 (2001)
603-607.
b. M. Toyota, C. Komori, M. Ihara, J. Org. Chem. 65 (2000) 7110- 7113.
63. a. H. Nakamura, M. Aizawa, D. Takeuchi, A. Murai, O. Shimoura,
Tetrahedron Lett. 41 (2000) 2185-2188.
b. G. Amiet, H.M. Hugel, F. Nurlawis, Synlett. (2002) 495-497.
64. a. S.A. Lawrence, Amines: Synthesis, Properties and Application, Cambridge
University Press, Cambridge, 2004.
b. J.F. Hartwig, Handbook of Organopalladium Chemistry for Organic
Synthesis, (Ed.: E.I. Negishi), Wiley, New York 1 (2002) 1051-1096.
65. S. Gladiali, E. Alberico, Chem. Soc. Rev. 35 (2006) 226-236.
66. R. Malacea, R. Poli, E. Manoury, Coord. Chem. Rev. 254 (2010) 729-752.
67. T. Ikariya, A.J. Blacker, Acc. Chem. Res. 40 (2007) 1300-1308.
68. R.A. Sheldon, J.K. Kochi, Metal-Catalyzed Oxidations of Organic
Compounds, Academic Press, New York, 1981.
69. A.E.J. de Nooy, A.C. Basemer, H.V. Bekkum, Synthesis (1996) 1153-1174.
70. I.W.C.E. Arends, R.A. Sheldon, Appl. Catal. A 212 (2001) 175-184.
71. J.A. Maga. CRC Crit. Rev. Food Sci. Nutr. 14 (1981) 295-307.
72. T.G. Gant, A.I. Meyers. Tetrahedron 50 (1994) 2297-2360.
73. a. G. Rosini, Comprehensive Organic Synthesis, B.M. Trost (Ed.) Pergamon,
New York 2 (1991) 321-340.
b. K. Iseki, S. Oishi, H. Sasai, M. Shibasaki, Tetrahedron Lett. 37 (1996)
9081-9084.
c. A. Barco, S. Benetti, C.D. Risi, G.P. Polloni, R. Romagnoli, V. Zanirato,
Tetrahedron Lett. 37 (1996) 7599-7602.
43
d. H. Sasai, M. Hiroi, Y. Yamada, M. Shibasaki, Tetrahedron Lett. 38
(1997) 6031-6034.
e. M. Shibasaki, H. Sasai, T. Arai, Angew. Chem. Int. Ed. Engl. 36 (1997)
1236-1256.
74. W. Jin, X. Li, Y. Huang, F. Wu, B. Wan, Chem. Eur. J. 16 (2010) 8259-
8261.
75. M. Milenkovic, A. Pevec, I. Turel, M. Vujcic, M. Milenkovi, K. Jovanovic,
N. Gligorijevic, S. Radulovic, M. Swart, M. Gruden-Pavlovic, K. Adaila,
B. Cobeljic, K. AnCelkovi, Eur. J. Med. Chem. 87 (2014) 284-297.
76. S. Guveli, T. Bal-Demirci, N. Ozdemir, B. Ulkuseven, Trans. Met. Chem. 34
(2009) 383-388.
77. S.V. Kolotilov, O. Cador, S. Golhen, O. Shvets, V.G. Ilyin,
V.V. Pavlishchuk, L. Ouahab, Inorg. Chim. Acta 360 (2007) 1883-1889.
78. S. Anitha, J. Karthikeyan, A. Nityananda Shetty, R. Lakshmisundaram,
Polyhedron 50 (2013) 264-269.
79. P. Kalpaga Suganthy, R. Narayana Prabhu, V. Shamugham Sridevi,
Tetrahedron Lett. 54 (2013) 5695-5698.
80. Saswati, R. Dinda, C.S. Schmiesing, E. Sinn, Y.P. Patil, M. Nethaji,
H. Stoeckli-Evans, R. Acharyya, Polyhedron 50 (2013) 354-363.
81. S. Priyarega, P. Kalaivani, R. Prabhakaran, T. Hashimoto, A. Endo,
K. Natarajan, J. Mol. Struct. 1002 (2011) 58-62.
82. N. Ain Mazlan, T.B.S.A. Ravoof, E.R.T. Tiekink, M.I. Mohamed Tahir,
A. Veerakumarasivam, K.A. Crouse, Trans. Met. Chem. 39 (2014) 633-639.
83. S. Datta, D. Kumar Seth, S. Gangopadhyay, P. Karmakar, S. Bhattacharya,
Inorg. Chim. Acta 392 (2012) 118-130.
84. R. Prabhakaran, R. Sivasamy, J. Angayarkanni, R. Huang, P. Kalaivani,
R. Karvembu, F. Dallemer, K. Natarajan, Inorg. Chim. Acta 374 (2011) 647-
653.
85. M. Muthu Tamizh, R. Karvembu, Inorg. Chem. Commun. 25 (2012) 30-34.
86. P. Kalaivani, S. Saranya, P. Poornima, R. Prabhakaran, F. Dallemer,
V. Vijaya Padma, K. Natarajan, Eur. J. Med. Chem. 82 (2014) 584-599.
44
87. R. Prabhakaran, R. Huang, S.V. Renukadevi, R. Karvembu, M. Zeller,
K. Natarajan, Inorg. Chim. Acta 361 (2008) 2547-2552.
88. V. Ruangpornvisuti, K. Supakornchailert, C. Tungchitpienchai, B. Wanno,
Struct. Chem. 17 (2006) 27-34.
89. K. Alomar, V. Gaumet, M. Allain, G. Bouet, A. Landreau, J. Inorg. Biochem.
115 (2012) 36-43.
90. S. Chandra, A. Kumar, Spectrochim. Acta A 67 (2007) 697-701.
91. S. Chandra, A. Kumar, Spectrochim. Acta A 66 (2007) 1347-1351.
92. F.J. Barros-Garcia, F. Luna-Giles, M.A. Maldonado-Rogado, E. Vinuelas-
Zahinos, Polyhedron 24 (2005) 2972-2980.
93. F. Kandemirli, T. Arslan, N. Karadayi, E.E. Ebenso, B. Koksoy, J. Mol.
Struct. 938 (2009) 89-96.
94. S. Goel, S. Chandra, S. Dhar Dwivedi, J. Chem. 2013 (2013) 1-7.
95. K.S. Abou-Melha, J. Coord. Chem. 61 (2008) 2053-2067.
96. B. Wang, Z.Y. Yang, M. Lu, J. Hai, Q. Wang, Z.N. Chen, J. Organomet.
Chem. 694 (2009) 4069-4075.
97. S. Guveli, B. Ulkuseven, Polyhedron 30 (2011) 1385-1388.
98. D.X. West, Y.Yang, T.L. Klein, K.I. Goldberg, A.E. Liberta, J. Valdes-
Martinez, S. Hernandez-Ortega, Polyhedron 14 (1995) 3051-3060.
99. S. Mathan Kumar, K. Dhahagani, J. Rajesh, K. Nehru, J. Annaraj,
G. Chakkaravarthi, G. Rajagopal, Polyhedron 59 (2013) 58-68.
100. V.M. Leovac, L.S. Jovanovic, V. Divjakovic, A. Pevec, I. Leban,
T. Armbruster, Polyhedron 26 (2007) 49-58.
101. V.M. Leovac, L.S. Jovanovic, V.S. Jevtovic, G. Pelosi, F. Bisceglie,
Polyhedron 26 (2007) 2971-2978.
102. R. Manikandan, P. Anitha, G. Prakash, P. Vijayan, P. Viswanathamurthi,
Polyhedron 81 (2014) 619-627.
103. F. Basuli, M. Ruf, C. G. Pierpont, S. Bhattacharya, Inorg. Chem. 37 (1998)
6113-6116.
104. F. Basuli, S.M. Peng, S. Bhattacharya, Inorg. Chem. 39 (2000) 1120-1127.
105. S. Dutta, F. Basuli, A. Castineiras, S.M. Peng, G.H. Lee, S. Bhattacharya,
Eur. J. Inorg. Chem. (2008) 4538-4546.
45
106. N. Saha Chowdhury, D. Kumar Seth, M.G.B. Drew, S. Bhattacharya, Inorg.
Chim. Acta 372 (2011) 183-190.
107. J.G. Malecki, A. Maron, M. Serda, J. Polanski, Polyhedron 56 (2013) 44-54.
108. D. Mishra, S. Naskar, M.G.B. Drew, S. Kumar Chattopadhyay, Inorg. Chim.
Acta 359 (2006) 585-592.
109. C. Rodrigues, A.A. Batista, R.Q. Aucelio, L.R. Teixeira, L. do Canto
Visentin, H. Beraldo, Polyhedron 27 (2008) 3061-3066.
110. M. Muthukumar, P. Viswanathamurthi, Cent. Eur. J. Chem. 8 (2010) 229-
240.
111. M. Muthukumar, S. Sivakumar, P. Viswanathamurthi, R. Karvembu,
R. Prabhakaran, K. Natarajan, J. Coord. Chem. 63 (2010) 296-306.
112. R. Prabhakaran, R. Huang, R. Karvembu, C. Jayabalakrishnan, K. Natarajan,
Inorg. Chim. Acta 360 (2007) 691-694.
113. P. Kalaivani, R. Prabhakaran, P. Poornima, F. Dallemer, K. Vijayalakshmi,
V. Vijaya Padma, K. Natarajan, Organometallics 31 (2012) 8323-8332.
114. R. Prabhakaran, P. Kalaivani, R. Jayakumar, M. Zeller, A.D. Hunter,
S.V. Renukadevi, E. Ramachandrana, K. Natarajan, Metallomics 3 (2011)
42-48.
115. P. Kalaivani, R. Prabhakaran, E. Vaishnavi, T. Rueffer, H. Lang,
P. Poornima, R. Renganathan, V. Vijaya Padma, K. Natarajan, Inorg. Chem.
Front. 1 (2014) 311-324.
116. S. Selvamurugan, R. Ramachandran, P. Viswanathamurthi, Biometals 26
(2013) 741-753.
117. G. Raja, C. Jayabalakrishnan, Cent. Eur. J. Chem. 11 (2013) 1010-1018.
118. P. Sengupta, R. Dinda, S. Ghosh, Trans. Met. Chem. 27 (2002) 665- 667.
119. V. Mahalingam, N. Chitrapriya, F.R. Fronczek, K. Natarajan, Polyhedron 29
(2010) 3363-3371.
120. V. Mahalingam, N. Chitrapriya, F.R. Fronczek, K. Natarajan, Polyhedron 27
(2008) 2743-2750.
121. F.A. Beckford, M. Shaloski Jr, G. Leblanc, J. Thessing, L.C. Lewis-
Alleyne, A.A. Holder, L. Li, N.P. Seeram, Dalton Trans. (2009) 10757-
10764.
46
122. M. Mohamed Subarkhan, R. Ramesh, Polyhedron 138 (2015) 264- 270.
123. P. Paul, D. Kumar Seth, M.G. Richmond, S. Bhattacharya, RSC Adv. 4
(2014) 1432-1440.
124. D. Pandiarajan, R. Ramesh, Inorg. Chem. Commun. 14 (2011) 686- 689.
125. S.I. Mostafa, A.A. El-Asmy, M.S. El-Shahawi, Trans. Met. Chem.25 (2000)
470-473.
126. D. Mishra, S. Naskar, M.G.B. Drew, S.K. Chattopadhyay, Inorg. Chim. Acta
359 (2006) 585-592.
127. N. Thilagavathi, A. Manimaran, N. Padma Priya, N. Sathya,
C. Jayabalakrishnan, Trans. Met. Chem. 34 (2009) 725-732.
128. S. Kannan, M. Sivagamasundari, R. Ramesh, Y. Liu, J. Organomet. Chem.
693 (2008) 2251-2257.
129. M. Ulaganatha Raja, N. Gowri, R. Ramesh, Polyhedron 29 (2010) 1175-
1181.
130. N. Raja, R. Ramesh, Spectrochim. Acta A 75 (2010) 713-718.
131. S. Selvamurugan, P. Viswanathamurthi, A. Endo, T. Hashimoto,
K. Natarajan, J. Coord. Chem. 66 (2013) 4052-4066.
132. S. Grguric-Sipka, C.R. Kowol, S.M. Valiahdi, R. Eichinger, M.A. Jakupec,
A. Roller, S. Shova, V.B. Arion, B.K. Keppler, Eur. J. Inorg. Chem. (2007)
2870-2878.
133. R. Manikandan, P. Viswnathamurthi, Spectrochim. Acta A 97 (2012)
864-870.
134. M. Maji, S. Ghosh, S.K. Chattopadhyay, T.C.W. Mak, Inorg. Chem. 36
(1997) 2938-2943.
135. E. Cabrera, H. Cerecetto, M. Gonzalez, D. Gambino, P. Noblia, L. Otero,
B. Parajon-Costa, A. Anzellotti, R. Sanchez-Delgado, A. Azqueta, A. Lopez
de Cerain, A. Monge, Eur. J. Med. Chem. 39 (2004) 377-382.
136. M. Nirmala, R. Manikandan, G. Prakash, P. Viswanathamurthi,
Appl. Organomet. Chem. 28 (2014) 18-26.
137. P. Sengupta, R. Dinda, S. Ghosh, W.S. Sheldrick, Polyhedron 22 (2003)
447-453.
47
138. F. Beckford, D. Dourth, M.Shaloski Jr, J.Didion, J. Thessing, J. Woods,
V. Crowell, N. Gerasimchuk, A. Gonzalez-Sarrias, N.P. Seeram, J. Inorg.
Biochem. 105 (2011) 1019-1029.
139. R. Ramachandran, G. Prakash, S. Selvamurugan, P. Viswanathamurthi,
J.G. Malecki, V. Ramkumar, Dalton Trans. 43 (2014) 7889-7902.
140. F.A. Beckford, J. Thessing, M. Shaloski Jr, P.C. Mbarushimana,
A. Brock, J. Didion, J. Woods, A. Gonzalez-Sarrias, N.P. Seeram, J. Mol.
Struct. 992 (2011) 39-47.
141. T. Stringer, B. Therrien, D.T. Hendricks, H. Guzgay, G.S. Smith,
Inorg. Chem. Commun. 14 (2011) 956-960.
142. Q. Zhou, P. Li, R. Lu, Q. Qian, X. Lei, Q. Xiao, S. Huang, L. Liu, C. Huang,
W. Su, Z. Anorg. Allg. Chem. 639 (2013) 943-946.
143. W. Su, Q. Zhou, Y. Huang, Q. Huang, L. Huo, Q. Xiao, S. Huang,
C. Huang, R. Chen, Q. Qian, L. Liu, P. Li, Appl. Organometal. Chem. 27
(2013) 307-312.
144. S. Huang, F. Zhu, Q. Xiao, Q. Zhou, W. Su, H. Qiu, B. Hu, J. Sheng,
C. Huang, RSC Adv. 4 (2014) 36286-36300.
145. M. Ulaganatha Raja, E. Sindhuja, R. Ramesh, Inorg. Chem. Commun. 13
(2010) 1321-1324.
146. F.A. Beckford, G. Leblanc, J. Thessing, M. Shaloski Jr, B.J. Frost, L. Li,
N.P. Seeram, Inorg. Chem. Commun. 12 (2009) 1094-1098.
147. W. Su, Q. Qian, P. Li, X. Lei, Q. Xiao, S. Huang, C. Huang, J. Cui,
Inorg. Chem. 52 (2013) 12440-12449.
148. R. Acharyya, S. Dutta, F. Basuli, S.M. Peng, G.H. Lee, L.R. Falvello,
S.Bhattacharya, Inorg.Chem. 45 (2006) 1252-1259.
149. I. Pal, S. Dutta, F. Basuli, S. Goverdhan, S.M. Peng, G.H. Lee,
S. Bhattacharya, Inorg. Chem. 42 (2003) 4338-4345.
150. D. Kumar Seth, S. Bhattacharya, J. Organomet. Chem. 696 (2011) 3779-
3784.
151. M.B. Ezhova, B.O. Patrick, B.R. James, M.E. Ford, F.J. Waller, Russ. Chem.
Bull. 52 (2003) 2707-2714.
48
152. M.B. Ezhova, B.O. Patrick, K.N. Sereviratne, B.R. James, F.J. Waller,
M.E. Ford, Inorg. Chem. 44 (2005) 1482-1491.
153. V.K. Sharma, S. Srivastava, A.Srivastava, Bioinorg. Chem. Appl. 2007
(2007) 1-10.
154. S. Dutta, F. Basuli, S.M. Peng, G.H. Lee, S. Bhattacharya, New J. Chem. 26
(2002) 1607-1612.
155. K. Mukkanti, R.P. Singh, Transition Met. Chem. 12 (1987) 299-301.
156. S.K. Chattopadhyay, M. Hossain, S. Ghosh, A. Kumar Guha,
Transition Met. Chem. 15 (1990) 473-477.
157. G. Muthusamy, P. Viswanathamurthi, M. Muthukumar, K. Natarajan,
Phosphorus Sulfur Silicon Relat. Elem. 184 (2009) 2115-2124.
158. R. Agarwal, M.A. Khan, S. Ahmad, J. Chem. Pharm. Res. 5 (2013) 240-245.
159. C.L. Jain, P.N. Mundley, J. Inorg. Nucl. Chem. 42 (1980) 1769-1770.
160. L. Singh, P. Gupta, U. Singh, I. Chakraborti, Asian J. Chem. 13 (2001) 740-
744.
161. M.S. El-Shahawi, M.S. Al-Jahdali, A.S. Bashammakh, A.A. Al-Sibaai,
H.M. Nassef, Spectrochim. Acta A 113 (2013) 459-465.