Self-assembled Transition Metal Coordination Frameworks of ...

3.3. Results and discussion
g_g _ Ni(H) complexes
The novel complexes l to 4 were synthesized by equimolar reaction between
NiCl2 and corresponding ligands and by the metathetical displacement of chloride ions
by PF; anions. The complexes 3 and 4, synthesized by carbohydrazone ligands, are
first of its kind. The carbohydrazones having well defined and appropriately separated
two coordination pockets, using the bridging mode of oxygen, in principle have a
better chance of control over the outcome of a self-assembly process to produce the
predefined Ni(II) nuclear molecular square, like Ni(II) thiocarbohydrazone grids.
However the formation of these kinds of materials are hard to prove with common
physico-chemical techniques, if the complexes lack stability. The Ni(II) grids 1 to 4,
fortunately seemed rigid framework even in solution phase, and soft ionization
technique of MALDI MS spectra reveal the formation of tetranuclear molecular
square natured structures. Molar conductivity measurement inl 0° M DMF solution of
2 (147 Q"cm2mol") showed a 2:1 electrolyte [26]. For all the other three
carbohydrazone and thiocarbohydrazone derived compounds the conductance values
obtained were ~30 Q"cm2 moi" in 104 M DMF solution. The complex 2 was assigned
the formula [Ni;,(HL3)L3]2(PF(,)2- 7H2O and I, 3, and 4 were assigned a general
formula [Ni(HL)]4[PF(,]4- nH2O (Scheme 3.1). The variable temperature magnetic
studies reveal intramolecular antiferromagnetic couplings. The theoretical simulations
of isotropic patterns of all molecular ion peaks and their fragmentation peaks of
MALDI MS spectra could be achieved well, and confirm the proposed structural
fonnulae. The structure of [Ni(HL1)]4(PF(,)4' ‘/zCH3CH2OH- 2.8l-I20 (la) is confirmed
by single crystal X-ray study and is in well agreement with mass spectral study of l.
The thiosemicarbazone complexes 5 and 6 are found to be six coordinate
around Ni(lI) centers based on spectral and room temperature magnetic susceptibility
studies, while the compound 7 is four coordinate around Ni(Il) center. The
stoichiometries of the complexes are in agreement with the partial elemental analyses
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