Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 2 1 g
anticipation of Cu(H) complexes of bis(pyridine-2-aldehyde) thiocarbohydrazone as
anticancer drug analogues of corresponding thiosemicarbazone complexes also
prompted us to select these potential class of ligands.
Carbohydrazones and thiocarbohydrazones have previously served as
chelating ligands to form mononuclear and dinuclear complexes [4,7-9]. The
capability of thiocarbohydrazones, with suitable substituents and reaction condition
for generating molecular squares were first reported by Duan er al. in 1997 [10] and
his groups [11,12] and later by Akbar Ali er al. [13]. Recently, two octanuclear Cu(Il)
complexes have been reported with 1,5-bis(2-hydroxybenzaldehyde)
thiocarbohydrazone ligand [14], where six of the seven donor atoms of
tetradeprotonated ligand in anti tautomeric form are linked with two metal ions to
form a dicopper(II) unit. The assembly of four such units into a metallo macrocyclic
array takes place by coordination of the seventh donor atom of each unit. However,
there was no earlier report of their oxygen analogues, carbohydrazones, acting as
building blocks for molecular frameworks through self-assembly [15]. With the
anticipation that carbohydrazones can also act as building blocks for self-assembly,
like thiocarbohydrazones, when suitable conditions are employed, we selected
carbohydrazones with suitable substituents. Conversely, the feel that it would be
worthwhile to study a comparison of the spectral behaviour and coordinating
properties between carbohydrazones and thiocarbohydrazones lead us to the synthesis,
structural and spectral studies of the following six ligands (Scheme 2.1).
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1. 1,5-Bis(di-2-pyridyl ketone) thiocarbohydrazone (H2L')
2. l,5-Bis(2-benzoylpyridine) thiocarbohydrazone (mt?)
3. 1,5-Bis(quinoline-2-carbaldehyde) thiocarbohydrazone (HZL3)
4. 1,5-Bis(di-2-pyridyl ketone) carbohydrazone (HZL4)
5. 1,5-Bis(2-benzoylpyridine) carbohydrazone (HZLS)
6. 1,5-Bis(quinoline-2-carbaldehyde) carbohydrazone (H2L(’)