Complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II) and Fe(III) with N′1,N′4-bis((1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)methylene) succinohydrazide are reported and characterized using various analytical and spectroscopic techniques like 1H NMR-, mass-, IR-, ESR-, UV-Vis. spectra, magnetic moment and molar conductivity measurements as well as elemental and thermal analyses. The ligand behaves as a dibasic hexadentate N2O4 bonded covalency via the enolic carbonyl oxygen of hydrazide moiety and coordeinated via carbonyl oxygen of antipyrine moiety and azomethine nitrogen atoms. Based on magnetic and electronic spectra data a distorted octahedral geometry around the metal ions has been proposed. The ESR spectrum of copper(II) complexes (3) showed axial symmetry with
$\text{g} \parallel \ge \text{g}\bot \ge {\rm g_e}$
, indicating a distorted octahedral structure and presence of the unpaired electron in d(x2-y2) orbital. The antimicrobial activities results of the metal complexes 2, 3, 4, 5, 8, 11, 13 and 16 show that, all these complexes exhibit moderate to mild inhibitory effects aganist Bacillus subtilis, Escherichia Coli and Aspergillus niger while the parent ligand is inactive. This enhancement may be attrubied to their structures which possess an additional C = N bond. Moreover, coordination reduces the polarity of the metal ion mainly because of the partial sharing of its positive charge with the donor atom within the chelate ring system, which formed during the coordination. This process, in turn, increases the lipophilic nature of the central metal atom, which favors its permeation more efficiently through the lipid layer of the microorganism thus destroying them more aggressively.
