Unique examples of copper(II)/sodium(I) and nickel(II)/sodium(I) Schiff base complexes with bridging bis-bidentate Salen type ligand: Synthesis, crystal structures and antibacterial studies

Abstract

Two unique heteronuclear Schiff base complexes of Cu(II), [{Cu(L)Na(ClO4)}2(μ-H2L)] (1) and Ni(II), [{Ni(L)Na(BF4)}2(μ-H2L)] (2) were synthesized and characterized by different spectroscopic methods as well as X-ray crystallography. The Schiff base ligand (H2L) was synthesized from the condensation meso-1,2-diphenyl-1,2-ethylenediamine with 3-methoxysalicylaldehyde. The 3d metal ions in these complexes have been accommodated by the inner N2O2 compartment of the Schiff base ligand, while the O2O′2 outer compartment has accommodated the Na(I) ion (O and O′ denote the phenolic and methoxy oxygen atoms, respectively). Besides, a Schiff base ligand has doubly bridged the M(II)/Na(I) moieties via the (OO′)2 coordination mode. This mode of bidentate action of a potentially tetradentate Schiff base ligand is very rare and has been observed for the first time in such 3d-ns complexes. The in vitro antibacterial activity of the Schiff base ligand and the complexes (1) and (2) were tested against human pathogenic bacteria such as Bacillus subtilis (Gram positive); Staphylococcus aureus (Gram positive); Salmonella typhi (Gram negative); and Escherichia coli (Gram negative). The results showed that these new hetero-polynuclear complexes had moderate antibacterial activity against both Gram type bacteria.