Mixed ligand Cu(II) complexes of an unsymmetrical Schiff base ligand and N-donor heterocyclic co-ligands: Investigation of the effect of co-ligand on the antibacterial properties

Abstract

In this study, two new and one previously reported mixed ligand Cu(II) complexes were synthesized and characterized. The complexes have general formula [Cu(L1)(L2)]ClO4 in which L1 is an NN′O type unsymmetrical tridentate Schiff base ligand and L2 is an N-donor heterocyclic ligand, i.e. 2,2′-bipyridine in complex (2), 4,4′-di-t-butyl-2,2′-bipyridine in (3) and 1,10-phenanthroline in (4). The Schiff base ligand is the mono-condensed form of the reaction between ethylenediamine with salicylaldehyde. The complexes were characterized by IR and UV–Vis spectroscopy, as well as elemental analyses. Crystal structures of two of the complexes (2 and 3) were also obtained by X-ray crystallography. The complexes were tested as antibacterial agents against two gram positive and two gram negative human pathogenic bacteria, i.e. Staphylococcus aureus (Gram positive), Bacillus subtilis (Gram positive), Salmonella typhi (Gram negative), and Escherichia coli (Gram negative). The precursor [Cu(L1)(py)]ClO4 complex (1) was also tested for comparison. The results showed that the complexes (1), (2) and (3) were moderately active against the studied bacteria, while complex (4) with 1,10-phenanthroline co-ligand showed very good antibacterial activity.