Synthesis, characterization, crystal structure and antioxidant activity of Ni(II) and Cu(II) complexes with 2-formilpyridine N(4)-phenylthiosemicarbazone

Abstract

New nickel(II) and copper(II) complexes, [Ni(HL)2]Cl2·2.5H2O (1), [Cu(L)Cl] (2), [Cu(HL)(H2O)](SO4) (5), [Cu(L)(X)(H2O)2] [X=Br− (3), OAc− (4), NO3− (6), ClO4− (7)] were synthesized with 2-formilpyridine N(4)-phenylthiosemicarbazone (HL·HCl). The thiosemicarbazone ligand was characterized by NMR (1H and 13C) spectroscopy and X-ray diffraction. All the complexes were characterized by electronic and FT-IR spectroscopy, molar conductivity, magnetic susceptibility measurements and elemental analysis. In addition, the copper(II) complexes were studied by EPR spectroscopy. Also, the crystal structures of complexes 1 and 2 were determined by single-crystal X-ray diffraction analysis. In the complex 1, the nickel atom exhibits a slightly distorted octahedral N4S2 coordination provided by two molecules of tridentate non-deprotonated ligand. The copper atom exhibits a distorted square-planar coordination environment in the complex 2 provided by one molecule of deprotonated ligand and one chloride anion. The free ligand and the metal complexes were screened for their antioxidant activity by free radical scavenging assays using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and compared with that of butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) standards.