Syntheses, crystal structures and antibacterial activities of zinc(II) complexes with Schiff base ligands

Abstract

Four new zinc(II) complexes, [Zn(HL1)I2] (1), [Zn(HL1)Br2] (2), [Zn(HL2)I2] (3) and [Zn3(CH3COO)2(L2)2(N3)2] (4), where L1 and L2 are the deprotonated form of 2-({[3-(dimethylamino)propyl]imino}methyl)-4-methoxyphenol (HL1) and 2-({[3-(diethylamino)propyl]imino}methyl)-4-methoxyphenol (HL2), respectively, were prepared and characterized by physico-chemical methods and single crystal X-ray diffraction. In the mononuclear complexes 1, 2 and 3, the Schiff bases HL1 and HL2 act as bidentate ligands, which coordinate to the Zn atoms through the phenolate oxygen and imine nitrogen atoms. In the trinuclear complex 4, the Schiff base HL2 acts as a tridentate ligand, which coordinates to the Zn atoms through the phenolate oxygen, imine nitrogen and amine nitrogen atoms. Single-crystal X-ray diffraction revealed that complexes 1–3 possess distorted tetrahedral Zn(II) coordination geometries, whereas trinuclear complex 4 contains Zn(II) centers with square-pyramidal and trigonal-bipyramidal coordination environments. Antibacterial activities against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens of the complexes were studied. The zinc(II) complexes exhibited enhanced antibacterial activities compared with the free Schiff bases, and complexes 1–3 showed particularly high activity against S. aureus, with MIC values of 1.56 μg mL−1.