Coordination versatility of N2O4 polydentate hydrazonic ligand in Zn(II), Cu(II), Ni(II), Co(II), Mn(II) and Pd(II) complexes and antimicrobial evaluation

New polydentate hydrazone ligand, was synthesized by the condensation of 1,5-dimethyl-3-oxo-2-phenylpyrazole-4-carbaldehyde with adipodihydrazide. The structure of the synthesized ligand, N′1,N′6-bis((1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl) methylene) adipohydrazide was elucidated by various analytical and spectroscopic techniques. The reactions of the ligand with zinc(II), copper(II), nickel(II), cobalt(II), manganese(II) and palladium(II) salts afforded homobinuclear metal complexes. Characterization and structure elucidation of the prepared complexes were achieved using different analytical and spectroscopic techniques. The analyses data indicated that this ligand behaved as N2O4 dibasic hexadentate ligand bonded covalency to the metal ions through the enolic carbonyl oxygen of hydrazide moiety and coordinated via carbonyl oxygen of antipyrine moiety and azomethine nitrogen atoms forming distorted octahedral geometry around the metal ions. The ESR spectra of copper(II) complexes (3) and (4) showed an axial symmetry with g||>g⊥>ge, indicating distorted octahedral structure and presence of the unpaired electron in d(x2−y2) orbital. The microbicide studies of the ligand and its metal complexes (2), (3), (4), (5), (8), (11) and (13) showed that, all these complexes exhibit moderate to mild inhibitory effects on B. subtilis, E. coli while complexes (2), (3), (4) and (13) exhibit moderate to mild inhibitory effects on A. niger.