Syntheses, spectroscopic characterization, SOD-like properties and antibacterial activities of dimer copper (II) and nickel (II) complexes based on imine ligands containing 2-aminothiophenol moiety: X-ray crystal structure determination of disulfide Schiff bases

A series of new dimer complexes of copper (II) and nickel (II) were designed and synthesized using the Schiff base ligands which was formed by the condensation of 2-aminothiophenol with 2- methoxybenzaldehyde, 3-formylbenzonitrile and 3-bromo-2-hydroxy-5-nitrobenzaldehyde, respectively. The synthesized metallic complexes were characterized by using different physicochemical and spectroscopic methods. The most plausible geometry for the 1:2 complexes appeared to be distorted square-planar or tetrahedral environments. All the synthesized metal complexes are found to be binuclear and confirmed by elemental analyses, magnetic susceptibility measurements and ESR spectroscopy. The Schiff base ligands (HL1/HL2/H2L) were coordinated to the metal ions through the ONS/SNN and/or N, S donor atoms. In order to prevent the oxidation of the thiol group during the formation of Schiff bases and its complexes, all of the reactions were carried out under an inert atmosphere of argon. The X-ray structures of the Schiff base ligands showed that in the crystalline form the SH groups were oxidized to produce a disulfide Schiff bases as a new double Schiff base ligands (L1a/L2a/H2La). The L1b ligand is a bicyclic ring system of N, S-containing heterocyclic. The crystal structures of the double Schiff bases were determined by single crystal X-ray diffraction. The molar conductivity values of the complexes in DMSO implied the presence of non-electrolyte species. The SOD-like activity of Schiff bases and its complexes were investigated by NBT-DMSO assay and IC50 values were evaluated. Their biological properties have also been studied. These complexes were also tested for their in vitro antibacterial screening activities against three bacteria (Streptococcus aureus, Salmonella typhi, and Escherichia coli) comparing with the Schiff base ligands. Most of the complexes have higher antibacterial activities than those of the free Schiff bases, double Schiff bases and the control.