1-(1H-Benzoimidazol-2-yl)-ethanone thiosemicarbazone (H2L) (1) was obtained by the condensation reaction of 2-acetylbenzimidazole, thiosemicarbazide and acetic acid in ethanol. The novel cobalt(III) complex [Co(L)(HL)] 2 was prepared by the direct reaction of CoCl2 center dot 6H(2)O with the ligand H2L. The reaction products were characterized by elemental analysis, thermogravimetric analysis (TGA), FT-IR and mass spectrometry for H2L, and magnetic measurement for the Co(III) complex. The crystal and molecular structures of complex 2 and the free ligand 1 were also determined by single-crystal X-ray structure analysis. The crystal structure data suggests that in compound 2, two ligands (H2L) coordinate to cobalt in a N2S tridentate fashion, giving a distorted octahedral geometry. Furthermore, compounds 1 and 2 were evaluated for their antimicrobial properties using a broth microdilution assay against various human pathogenic bacteria and the yeast Candida tropicalis, resulting in moderate minimum inhibitory concentrations (MIC = 0.25-1 mg/mL) when compared to standard antimicrobial agents. The free radical scavenging activity of the compounds against 1,1-diphenyl-2-picrylhydrazyl hydrate (DPPH) was also investigated. (C) 2008 Elsevier Ltd. All rights reserved.