Synthesis,characterization, and X-ray crystal structures of metal complexes with new Schiff-base ligands and their antibacterial activities

Two new potentially hexadentate Schiff bases, H₂L¹] and H₂L²], were prepared by condensation of 2-(3-(2-aminophenoxy)naphthalen-2-yloxy)benzenamine with 3,5-di-tert-butyl-2-hydroxy benzaldehyde and o-vanillin, respectively. Reaction of these ligands with cobalt(II) chloride, copper(II) perchlorate, and zinc(II) nitrate gave complexes ML. The ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution state investigations show that the complexes are neutral. Molecular structures of CuL¹], CoL¹]?·?C₇H₈, and ZnL²]?·?CH₃CN, which have been determined by single-crystal X-ray diffraction, indicate that CuL¹] and ZnL²]?·?CH₃CN display distorted square planar and distorted trigonal-bipyramidal geometry, respectively; the geometry around cobalt in CoL¹]?·?C₇H₈ is almost exactly between trigonal bipyramidal and square pyramidal. The synthesized ligands and their complexes were screened for their antibacterial activities against eight bacterial strains and the ligands and complexes have antibacterial effects. The most effective ones are CuL²] against Proteus vulgaris, Serratia marcescens, Staphylococcus subtilis, H²L¹] against S. subtilis, and H₂L²] against S. subtilis.