Synthesis, spectral and single crystal X-ray diffraction studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with o-amino acetophenone benzoyl hydrazone

A series of metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) with o-amino acetophenone benzoylhydrazone (HL) have been synthesized. The complexes were characterized by elemental analyses, magnetic susceptibility measurements, electronic, IR, NMR and ESR spectral techniques. The molecular structures of the Co(II) and Ni(II) complexes were determined by single crystal X-ray diffraction studies. The delocalized charge on the five-membered chelate rings of the Co(II) and Ni(II) complexes forms an unusual intra-molecular CH center dot center dot center dot pi interaction with the -CH3 hydrogen. CH center dot center dot center dot pi interactions were also observed in the Ni(II) complex between the phenyl ring and phenyl hydrogen. HL acts as a tridentate ligand in most of the complexes, bonding through >C=O, >C=N and -NH2 groups. Electronic spectral studies indicate an octahedral geometry for the Co(II) and Ni(II) complexes, but a square planar geometry for the Cu(II) complex. The ESR spectra of the Cu(II) complex also suggest a square planar geometry around the metal ion in the solid state, but a tetragonal distorted octahedral geometry in DMSO solution at LNT due to solvent interactions at the axial positions. The electrochemical study of the Cu(II) complex exhibits reversible redox behaviour. The thermal analyses (TGA and DTA) of a few complexes show an exothermic multi-step decomposition pattern of the bonded ligands. (C) 2013 Elsevier Ltd. All rights reserved.