Synthesis, structure characterisations and biological activities of 1-1[H-benzoimidazol-2yl]-ethanone thiosemicarbazone ligand and its Co and Zn complexes

In this study, new metal complexes of 1-1[H-Benzoimidazol-2yl]-Ethanol Thiosemicarbazone with Zn(II), Co(III), Fe(II), Mn(II) metal ions were synthesized. Crystal structures of free ligant, Co(III) and Zn(II) complexes are determined.Ligant and metal complexes are characterized by elemental analyses, FT-IR, 1H NMR spectroscopy, thermo gravimetric analysis (TGA). The crystal and molecular structures of Co (III) complex, Zn (II) complex and free ligant are also determined by single-crystal X-ray structure analysis.The crystal structure data shows that in Co (III) complex, two ligants (H2L) coordinate to cobalt atom in a N2S tridentate fashion, giving a distorted octahedral geometry. On the other hand, the coordination geometry of the penta coordinated zinc is described as an intermediate between the ideal trigonal bipyramid and a square pyramid including one N (H2L) and one S (H2L) atom occupying the apical sites of the molecule. Ligant is bonded to a zinc atom as tridentant by N2S structure.Furthermore, Co(III) complex and free ligant were evaluated for their antimicrobial properties using a broth microdilution method against various human pathogenic bacteria and the yeast C. tropicalis resulting in moderate minimum inhibitory concentrations of 0.25-1 mg/mL when compared with standard antimicrobial agents. The biological activity of Zn(II) complex was also investigated. The antimicrobial activity of the Zn(II) complex was evaluated by using a broth micro-dilution method against a panel of human pathogenic Gram positive, Gram negative bacteria and the yeast Candida albicans. The best inhibitory effect of Zn(II) complex was observed against Enterobacter aerogenes (MIC= 0.031 mg/ml). The free radical scavenging activity of the ligant and Co(III) complex using 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) was also investigated.