The manganese(II) and cobalt(II) complexes of enrofloxacin showed comparable antibacterial activity: Synthesis, crystal structure and antibacterial activity.

• The crystal structures of Mn(II)/Co(II) complexes of enrofloxacin (EFX) are reported. • Both complexes could maintain the coordinated status in aqueous solution. • Both complexes show comparable antibacterial activity to EFX. • They exhibit slight higher antibacterial activity than EFX towards E. coli & S. typhi. Enrofloxacin (EFX) is a third-generation fluoroquinolone drug especially used for animals world wide, which shows broad-spectrum and significant antibacterial activities. In this study, EFX was selected as the ligand to synthesize two transition metal complexes, EFX-Mn and EFX-Co, in which the bio-active metal ions, manganese(II) and cobalt(II), was set to be the active metal center. Their crystal structures were reported and characterized by X-ray single crystal diffraction analysis. Both the crystal structures of EFX-Mn and EFX-Co belong to the same monoclinic crystal system with P2 1 /c space group. Viewed from the crystal structure of EFX-Mn or EFX-Co, the central Mn(II)/Co(II) adapted a six-coordinated octahedral configuration, respectively by two EFX ligands and two H 2 O co-ligands. The characteristic UV-Vis absorption peaks of both complexes were examined in tris-saline buffer solution in a time-dependent mode in 24 h, which suggested that the coordination status of EFX-Mn and EFX-Co in the solid state still maintained under near-physiological condition. In vitro antibacterial activity tests demonstrated that EFX-Mn and EFX-Co showed similar and significant growth inhibitory effects towards five typical pathogenic bacteria, compared with EFX itself. While for two gram-negative bacterial strains, E. coli and S. typhi , EFX-Mn and EFX-Co showed higher bactericidal effects than EFX, the bactericidal concentration of which was only a half as low as that of EFX. The manganese(II) and cobalt(II) complexes of enrofloxacin were reported and their crystal structures were characterized. It indicated that the coordination of enrofloxacin with Mn(II) and Co(II) maintained the antibacterial activity in vitro , and showed superiority towards E. coli & S. typhi , making both complexes promising metal-based veterinary drugs. [Display omitted] [ABSTRACT FROM AUTHOR]