Synthesis and characterization of transition metal complexes of a hexadentate N4O2 donor Schiff base ligand: X-ray crystal structures of the copper(II) and zinc(II) complexes and their antibacterial properties

Abstract

A potentially hexadentate N 4 O 2 Schiff base ligand, L, has been synthesized by condensation of an aromatic diamine with 2-pyridinecarbaldehyde. The complexes [MLNO 3 ]NO 3 (M=Cu, Ni, Cd or Zn) and [MlCl 2 ] (M=Co or Mn) were synthesized by the reactions of L with metal salts in methanol. Both free L and its complexes were characterized by physicochemical and spectroscopic methods. In addition, the crystal structures of [CuLNO 3 ]-NO 3 and [ZnLNO 3 ]NO 3 have been determined by singlecrystal X-ray diffraction. In both complexes, the ligand L is coordinated via pyridine and azomethine nitrogen atoms to give a distorted octahedral geometry. These complexes have antibacterial activities against three Gram-positive and three Gram-negative bacteria, which in most cases exceed those of tobramycin and tetracycline as standards.