New nickel(II) complexes containing N2O2 donor thiosemicarbazones: Synthesis, characterization and antioxidant properties

Abstract

Six nickel(II) complexes containing N2O2 chelating thiosemicarbazones were synthesized using N1-3/4/5-methoxysalicylidene-S-methyl/propyl thiosemicarbazones and 4-benzyloxy- salicylaldehyde in the presence of Ni(II) ion by template reaction. The structures of synthesized compounds were characterized by elemental analysis, UV-Vis, IR and 1H-NMR spectroscopies. The structures of two complexes, N1-4-methoxysalicylidene-N4-4-benzyloxysalicylidene-S-methylthiosemicarbazidato nickel(II) (3) and N1-5-methoxysalicylidene-N4-4-benzyloxysalicylidene-S-propylthiosemicarbazidato nickel(II) (6), were determined by X-ray single-crystal diffraction method. The total antioxidant capacities of thiosemicarbazones and nickel(II) complexes were evaluated by using cupric reducing antioxidant capacity (CUPRAC) method. The obtained trolox equivalent antioxidant capacity (TEAC) values of the thiosemicarbazones were higher than nickel(II) complexes. 5-methoxy substitute derivatives (L5, L6) exhibited the highest activity in thiosemicarbazone compounds. The hydroxyl radical, DPPH radical and ABTS radical scavenging ability of the compounds were also evaluated.