Template synthesis, and X-ray crystal structures of copper(II) and nickel(II) complexes of new unsymmetrical tetradentate Schiff base ligands. Electrochemistry, antibacterial properties, and metal ion effect on hydrolysis-recondensation of the ligand

Two metal complexes, [Cu-II(naphsal)] (1), and [Ni-II(salnaph)] (2), of two new unsymmetrical tetradentate Schiff base ligands, H(2)naphsal {H(2)naphsal = N-naphthylidene-N'-salicylidene-2-aminobenzylamine} and H(2)salnaph {H(2)salnaph = N-salicylidene-N'-naphthylidene-2-aminobenzylamine} have been synthesized by metal template reaction of a tridentate Schiff base, Hnaphtabza {Hnaphtabza = N-(naphthylidene)-2-aminobenzylamine} and salicylaldehyde in the presence of the corresponding metal acetate. The dianionic naphsal(2) ligand, produced in the presence of Cu(II), is a simple template condensation product, while the dianionic salnaph(2) ligand, produced in the presence of Ni(II), is the hydrolytically rearranged isomer of naphsal(2). The copper(II) and nickel(II) complexes have been fully characterized and their crystal structures have been determined by single crystal X-ray diffraction. Both copper(II) and nickel(II) ions adopt a distorted square planar geometry. The cyclic voltammetric studies of 1 and 2 in acetonitrile solution showed that the Cu-II/Cu-I and Ni-II/Ni-I reduction processes are electrochemically reversible. The metal complexes were also screened for their in vitro antimicrobial activity. (C) 2015 Elsevier B.V. All rights reserved.