Bischelated complexes of a dithiocarbazate N,S Schiff base ligand: synthesis, characterization and antimicrobial activities

Abstract

The N,S bidentate proligand S-hexyl-β-N-(4-methoxybenzylidene)dithiocarbazate (HL), obtained by condensation of S-hexyldithiocarbazate with 4-methoxybenzaldehyde, has been used to synthesize six metal complexes, namely NiL2, CuL2, ZnL2, CdL2, PdL2 and PbL2, which have been characterized by physicochemical techniques and spectroscopic methods. Single crystal structural analyses for NiL2, CuL2 and PdL2 show that these are square-planar complexes with each metal bischelated by the Schiff base in its deprotonated monoanionic form. In all three cases, the ligands show a trans configuration, although they crystallize in different space groups. All the metal complexes with the exception of the nickel derivative show a significant decrease in fluorescence intensity with respect to the free proligand HL. Free HL and all six complexes were tested for antibacterial activity against three pathogenic gram-negative organisms. The metal complexes show moderate although diverse activities; however, free HL as well as the copper(II) complex did not reveal any antibacterial activity against the tested organisms.