Synthesis, Characterization and X-Ray Crystal Structures of Schiff Base Zinc(II) Complexes with Antibacterial Activity

Two mononuclear zinc(II) complexes [ZnCl2(HL)] (1) and [ZnBr2(HL)] (2), and a polymeric zinc(II) complex [Zn(dca)L] (3), where HL is the zwitterionic form of the Schiff base 2,4-difluoro-6-(((2-pyrrolidin-1-yl)ethylimino)methyl)phenol (HL), L is the monoanionic form of HL, and dca is dicyanoamide, were prepared and characterized by elemental analysis and infrared spectroscopy, as well as X-ray single crystal determination. Complexes 1 and 2 are isostructural, in which the Zn atoms are in tetrahedral coordination. The Schiff base ligands in both complexes are coordinate to the Zn atoms through phenolate oxygen and imino nitrogen. The zinc atoms in complex 3 are in tetrahedral coordination and are bridged by dicyanoamide ligands. The Schiff base ligand in this complex is coordinates to the zinc atom through phenolate oxygen, imino nitrogen and pyrrolidine nitrogen. Molecules of the three complexes are stabilized by hydrogen bonds. The biological assay indicates that the complexes have good antimicrobial activities on the bacteria strains Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi and Staphylococcus aureus.