Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 3 _ _____
can be related to an increase in the lipophilicity, so they can penetrate into the cells
more easily [5,7].
The idea of establishing control and predictability over molecular
architectures is of much interest. Molecular squares are one of the simplest but
nonetheless interesting members of the family of polygons and have received the
highest attention. Strategies to produce molecular square gridsof transition metal
centers include judicial utilization of the organizing ability of a polyfiinctional ligand
to suitable metal ions. Ni(II) is one of the most frequently used metal ion for
octahedral centers and are rare for self assembled molecular squares of multidentate
ligands [8]. The inclusion of magnetic metal ions like Ni(II) with these polynuclear
complexes added a new dimension, which leads nanometer-sized magnetic clusters of
versatile magnetic properties. Of these, the grid structures are of special interest in
information storage and processing technology [9]. Moreover, depending on the
packing or metal centers with suitable ligands, such assemblies of grids may result
molecular magnets. Nickel(lI) is known to have a large single-ion zero-field splitting
and often gives rise to ferromagnetic coupling [10], thus polynuclear nickel(II)
complexes are potential candidates for single molecule magnets also.
Ni complexes of carbohydrazones and thiocarbohydrazones are least studied.
Literature survey shows that mononuclear Ni(II) complexes of thiocarbohydrazide
[ll], 1,1’-diacetyl ferrocene-derived carbohydrazone [12], l,l’-diacetyl fenocenederived
thiocarbohydrazone [1 2], bis-(1 , l ’ -disubstituted ferrocenyl)
thiocarbohydrazone [13] and bis-( 1,1’-disubstituted ferrocenyl) carbohydrazone [13]
are reported. Mononuclear Ni(II) complexes derived from thiocarbohydrazide and
benzil have also been reported [14]. [n addition, a dinuclear Ni(Il) complex of 5­
chlorosalicylaldehyde thiocarbohydrazone has been reported recently [15]. A
molecular square complex of bis(2-benzoylpyridine) thiocarbohydrazone (HZLZ) [8]
and another one of bis(2-acetylpyridine) thiocarbohydrazone [16] have also been
reported. However, there are many reports of tetranuclear Ni(I1) complexes [17-22]
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