Synthesis, characterization, and biological activity studies on (E)-N'-[2-hydroxy-1,2-di(pyridin-2-yl)ethylidine]aroyl hydrazides and their copper(II) complexes

The reaction of copper(II) salts with (E)-N-(2-hydroxy-1,2-di(pyridin-2-yl)ethylidene)aroyl hydrazide (H2L1, H2L2, H3L3) or (E)-N-(2-hydroxy-1,2-di(pyridin-2-yl)ethylidene) isonicotinohydrazide (H2L4) afforded the complexes [(L)Cu(H2O)3], [(H2L)Cu(OAc)(H2O)], [(HL)Cu(OAc)]n, [(H2L)Cu(H2O)](ClO4)2 and [(H2L)Cu(OAc)(H2O)], where n = 1 or 2 and L is the dinegative ion of the ligands. The ligands and their complexes are characterized by elemental analyses, spectral (IR, NMR, electronic, and ESR) and magnetic studies. The FT-IR indicates that the ligands are neutral or anionic polydentate. The number of the coordinating centers depends on the nature of the metal used and the reaction conditions. The room temperature magnetic moment values, electronic spectra and ESR data indicate square planar, trigonal bipyramidal, square pyramidal, and distorted octahedral ligand fields around copper(II). Thermal decomposition of the complexes was monitored by TG and DTG under N2 and the thermal decomposition mechanisms are given. The compounds were screened for their antimicrobial activities on some Gram-positive and Gram-negative bacterial species. The free ligands are inactive against all studied bacteria. The complexes have variable activity with the most active [(H2L)Cu(H2O)](ClO4)2, where H2L is H2L1 or H2L2. The minimum inhibition concentrations for these two complexes were determined. These biological activity results are related to the structures of the compounds.