Square-planar and octahedral nickel complexes of an acylhydrazone ligand and the serendipitous isolation of a potential octahedral nickel acylhydrazone precursor

An investigation of the coordination chemistry of the ((E)-N'-(4-hydroxybenzylidene)-4-hydroxybenzohydrazide) Schiff-based ligand (HL) towards Ni(II) acetate was performed using single crystal X-ray diffraction. The compounds [Ni(L)(2)]center dot H2O (2) and [Ni(HL)(2)(H2O)(2)](CH3CO2)(2)center dot 2CH(3)CH(2)OH (1a) were isolated. Also, two solvated complexes of general formula [Ni(L)(2)]center dot solvent (2a, 2b) could be obtained as single crystals. Theoretical calculations were performed to evaluate the formation of the square-planar complex 2 from the octahedral 1a and to study the thermodynamic stability of the different compounds. The study of the reactivity of 2 with 1,2-di(4-pyridyl)ethylene (bpe) yielded single crystals of [Ni(L)(2)(bpe)(2)]center dot solvent (3).