Self-assembled Transition Metal Coordination Frameworks of ...

CHAPTER
Ni(II) complexes of carbohydrazone,
thiocarbohydrazone and thiosemicarbazone
ligands: Structural, spectral and magnetic properties
3.1. Introduction
The coordination complexes of nickel have been the subject of interest
especially for their magnetic and electronic behavior. The most stable and most
common oxidation state of nickel is +2, though 0, +1, +3 and +4 Ni complexes are
observed [l]. In the divalent state nickel exhibits wide and interesting variety of
coordination numbers and stereochemistries. Several factors have been recognized to
be particularly important in the stabilization of the +3 and +1 oxidation states, namely
coordination number, geometry, type of donor atom and electronic characteristics of
the ligand. Preparation of even zerovalent nickel complexes from elemental nickel has
been reported [2]. Coming to the biomimetic chemistry, nickel is recognized as an
essential trace element for bacteria, plants, animals and humans [3] and is one of the
most toxic metal among transition metals [4]. It shows the toxicity even in low doses
to both plants and animals. Epimediological data and animal study confirm that
crystalline nickel compounds are carcinogenic, while amorphous nickel compounds
are weak or non-carcinogenic. Ni complexes of some thiosemicarbazones and
semicarbazones have been screened in vitro against MCF-7 breast cancer cell lines for
their antiproliferation activity [5]. It is clearly observed that ligands on complexation
with metal ion increase the inhibitory action on MCF-7 cell proliferation. Similar
effect was observed upon complexation of some other thiosemicarbazones with
nickel(ll) ion [6]. The enhancement of antiproliferation activity by metal complexes