Spectroscopic and biological studies of mono- or binuclear complexes derived from thio-Schiff bases of some transition metals

Two novel Schiff base ligands, 4,6-bis((E)-1-(2-mercaptophenylimino)ethyl)benzene-1,3-diol, H4La, and 1,2-((E)-1-(6-((E)-1-(2-mercaptophenylimino)ethyl)pyridine-2-yl)ethylideneamino)benzenthiol, H2Lb, have been synthesized by the condensation of 4,6-diacetyl resorcinol (DAR) or 2,6-diacetyl pyridine (DAP) with 2-aminobenzenthiol (ABT), in the molar ratio 1:2 [1 (DAR or DAP):2 ABT]. The structures of ligands were elucidated by elemental analysis, infrared (IR), UV-VIS as well as 1H-NMR. Reaction of the Schiff base ligands with the transition metals Co(II), Ni(II), Cu(II), Zn(II), VO(IV) and Ru(III) afforded two series of the corresponding transition metal complexes in the molar ratio 1:2 or 1:1. The ligand, H4La, behaves as tetrabasic hexadentate, which hosts the two metal ions at the centers of two SNO sites, while H2Lb acts as a compartmental dibasic pentadentate ligand forming mono- or binuclear complexes through the coordinate sites N3S2. The structures of the newly prepared complexes were characterized on the basis of the elemental analysis, spectroscopic data (IR, UV-VIS, 1H-NMR and ESR spectra along with magnetic susceptibility measurements) besides the molar conductance measurements and thermal gravimetric analyses. The bonding sites are the azomethane, sulfur atoms and phenolic oxygen for H4La or pyridine nitrogen for H2Lb. The complexes exhibit mono- or binuclear structures, distorted octahedral, tetrahedral, square planar or square pyramid structure. Synthesized compounds have also been screened for their biological activity against species of pathogenic fungi and bacteria and were found to possess appreciable fungicidal and bactericidal properties.