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

Abstract

Two metal complexes, [CuII(naphsal)] (1), and [NiII(salnaph)] (2), of two new unsymmetrical tetradentate Schiff base ligands, H2naphsal {H2naphsal=N-naphthylidene-N′-salicylidene-2-aminobenzylamine} and H2salnaph {H2salnaph=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 naphsal2− ligand, produced in the presence of Cu(II), is a simple template condensation product, while the dianionic salnaph2− ligand, produced in the presence of Ni(II), is the hydrolytically rearranged isomer of naphsal2−. 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 CuII/CuI and NiII/NiI reduction processes are electrochemically reversible. The metal complexes were also screened for their in vitro antimicrobial activity.