Synthesis, structural characterisation and antibacterial activities of lead(II) and some transition metal complexes derived from quinoline-2-carboxaldehyde 4-methyl-3-thiosemicarbazone

Abstract

Some metal complexes of formulae, [PbHNNS(NO3)2], [Cu(NNS)], [Zn(NNS)2], [Ni(NNS)2] and [Cd(NNS)2] (NNS = anionic form of the Schiff base of quinoline-2-carboxaldehyde 4-methyl-3-thiosemicarbazone) have been synthesised and structurally characterised by a variety of physico-chemical techniques. The crystal structure of [PbHNNS(NO3)2] and [Zn(NNS)2] have also been determined by X-ray crystallography. The mono-ligated nitrato-complex adopts a distorted square pyramidal geometry where the thiosemicarbazone ligand coordinates to the lead(II) ion as a uninegatively charged bidentate NS chelating agent via the azomethine nitrogen atom and the thiolate sulphur atom. The third and fourth coordinations are occupied by two nitrato ligands. In the bis-ligand zinc(II) complex [Zn(NNS)2], the zinc atom adopts a distorted octahedral geometry around the zinc(II) ion, with two uninegatively charged tridentate NNS thiosemicarbazone ligands coordinating via one of the quinoline nitrogen atom, the azomethine nitrogen atom and the mercaptide sulphur atom displaying meridional coordination. Some of the metal complexes exhibit greater antibacterial activity against the Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli, as compared to the parent Schiff base ligand.