Synthesis, characterization, crystal structure and antimicrobial activity of copper(II) complexes with a thiosemicarbazone derived from 3-formyl-6-methylchromone

Abstract Six new copper(II) complexes, [CuLSO 4 CuL][CuL(H 2 O)] 2 (HSO 4 ) 2 10.5H 2 O ( 1 ), [Cu(HL)Br 2 ] ( 2 ), [Cu(L) 2 ] ( 3 ), [Cu(L)(OAc)(H 2 O)] ( 4 ), [Cu(L)(ClO 4 )(H 2 O)] ( 5 ) and [Cu(L)(NO 3 )(H 2 O) 2 ] ( 6 ), were synthesized with 3-formyl-6-methylchromone-4-phenylthiosemicarbazone ( HL ). The characterization of the complexes was done by electronic and IR spectroscopy, EPR studies, molar conductivity, magnetic susceptibility measurements and elemental analysis. The thiosemicarbazone ligand was characterized by NMR ( 1 H and 13 C) spectroscopy. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis. In the tetranuclear complex [CuLSO 4 CuL][CuL(H 2 O)] 2 (HSO 4 ) 2 10.5H 2 O ( 1 ) each copper atom exhibits a slightly distorted square-planar environment, provided by the anionic tridentate ligand and one oxygen atom originating from either a water molecule or the SO 4 2− anion. The copper atom in the monomer complex [Cu(HL)Br 2 ] ( 2 ) is in a square-pyramidal environment provided by the neutral tridentate ligand and two bromide anions. The antibacterial and antifungal activities of the copper(II) complexes and the free ligand against Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATTC 29212, Eescherichia coli ATTC 8739, Salmonella enteritidis ATCC 13076 and Candida albicans ATCC 10231 were determined. All the copper(II) complexes exhibited antimicrobial activity, especially complex 5 which showed the highest activity against all the strains (with MIC values of 16–64 μg/mL).