Self-assembled Transition Metal Coordination Frameworks of ...

_ _ __ g_ g W g H__ Ni(ll) complexes
and square grids [23,24] of other ligands, and they have made a great stimulus in the
metallosupramolecular chemistry.
Paramagnetic Ni(ll) complexes having sulfur/oxygen bridged are warranted
as there are only few complexes that have been subjected to variable-temperature
magnetic susceptibility studies. It has been shown that HZLZ [8] can connect two Ni(II)
ions, generating sulfur-bridged molecular square complexes. However no magneto­
structural correlation has yet been reported for these classes of complexes. Also, it is
found desirable to construct new sulfur-bridged paramagnetic Ni(lI) complexes. On
the other hand, there are no reports of magnetically coupled Ni(II) molecular squares
of carbohydrazone ligands. Transition metal template cyclizations have successfully
produced some tetranuclear nickel complexes [17-20], in which the metal ions are
bridged exclusively by oxygen donor groups. The anticipation that carbohydrazones
can also produce Ni(II) molecular square grids when suitable conditions are employed
by making use of oxygen bridge lead us to synthesize novel class of compounds. Also,
the complexing ability of NNS thiosemicarbazones is closely related to that of
thiocarbohydrazones as the former has one common coordination pocket with the
latter. There are reports of octahedral complexes of Ni(ll) thiosemicarbazones derived
from di-2-pyridyl ketone [25]. So it is worthwhile to report the structural
characterizations of few novel octahedral Ni(II) complexes of I-IL7 and HL8, having
the same aldehydic or ketonic part of thiocarbohydrazone and carbohydrazone ligands
(HZLZ, HZL3, HZLS and I-I2L°), as additional support for the formation of their higher
class of compounds. This is found necessary especially to establish the coordination
behaviour of novel quinoline-2-aldehyde derived ligand l-IL7 and thereby to check any
possibility of sterical hindrance for the formation of complexes having octahedral
geometries with novel quinoline-2-aldehyde derived carbohydrazone and
thiocarbohydrazone.
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