Synthesis, molecular structure and antioxidant activity of bis [L(μ2-chloro)copper(II)] supported by phenoxy/naphthoxy-imine ligands.

A new series of Cu(II) complexes [bis[{(μ2-chloro)-2-MeO-Ph-CH2-(N=CH)-2,4-tert-butyl-2-OC6H2)}Cu(II)] (Cu1); bis[{(μ2-chloro)-2-MeS-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(OC6H2)}Cu(II)] (Cu2); bis[{(μ2-chloro)-2-MeO-Ph-CH2-(N=CH)-2-(OC10H6)} Cu(II)] (Cu3); bis[{(μ2-chloro)-2-MeS-Ph-CH2-(N=CH)-2-(OC10H6)}Cu(II)] complex (Cu4); bis[{2-MeS-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(OC6H2)}Cu(II)] (Cu5)] have been synthesized and characterized by elemental analysis, IR, UV-Visible and by X-ray crystallography for Cu1, Cu4 and Cu5. In the solid state, Cu1 features of a chloro-bridged dimer complex with κ2 coordination of the monoanionic phenoxy-imine ligand onto the copper center. On the other hand, the molecular structure of Cu4 reveals the naphthoxy-imine ligand with pendant S-group coordinated to the copper atom in tridentate meridional fashion. Treatment of [Cu(OAc)2·H2O] with two equiv. of [2-MeS-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(HOC6H2)] led to a monomeric complex Cu5, with the ONS-donor Schiff base acting as a bidentate ligand. The redox behavior was explored by cyclic voltammetry. The reduction/oxidation potential of Cu(II) complexes depends on the structure and conformation of the central atom in the coordination compounds. Antioxidant activities of the complexes, Cu1 - Cu5, were determined by in vitro assays such as 1,1-diphenyl-2-picryl-hydrazyl free radicals (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radicals (ABTS+). The dinuclear compounds Cu1-Cu4, from the concentration of 5 μM, presented a good activity in scavenging DPPH radical. In addition, most of the Cu(II) complexes showed ABTS.+ radical-scavenging activity. The monomeric complex Cu5 at all concentrations tested showed antioxidant inability. The cytotoxicity of the Cu1 and Cu3 was determined in V79 cell line by reduction of 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay.