Syntheses, crystal structures and antimicrobial activities of 6-coordinate antimony(III) complexes with tridentate 2-acetylpyridine thiosemicarbazone, bis(thiosemicarbazone) and semicarbazone ligands

Abstract

Five novel antimony(III) complexes with the mono- and bis(thiosemicarbazone) ligands of 2N1S or 4N2S donor atoms, N′-[1-(2-pyridyl)ethylidene]morpholine-4-carbothiohydrazide (Hmtsc, L1) and bis[ N′-[1-(2-pyridyl)ethylidene]]-1,4-piperazinedicarbothiohydrazide (H 2ptsc, L7), and the tridentate semicarbazone ligand of 2N1O donor atoms, 2-acetylpyridine semicarbazone (Hasc, L2b), were prepared by reactions of SbCl 3 or SbBr 3, and characterized by elemental analysis, TG/DTA, FT-IR and 1H NMR spectroscopy. The crystal and molecular structures of five antimony(III) complexes were determined by single-crystal X-ray structure analysis. The neutral, 6-coordinate antimony(III) complexes ([Sb(mtsc)Cl 2] 1, [Sb(mtsc)Br 2] 2, [Sb(asc)Cl 2] 3 and [Sb(asc)Br 2] 4) are depicted with one electron pair (5s 2) of the antimony(III) atom, deprotonated forms of multidentate thiosemicarbazone or semicarbazone ligands, and two monodentate halogen ligands, respectively. In the dimer complex 5 ([Sb 2(ptsc)Cl 4]) with the ligand in which two tridentate thiosemicarbazone moieties are connected by the piperazine moiety, each antimony(III) was also described as a neutral 6-coordinate structure. These antimony(III) complexes were thermally stable around 200 °C. Water-soluble antimony(III) complexes 1 and 2 showed moderate antimicrobial activities against Gram-positive ( Bacillus subtilis and Staphylococcus aureus) and -negative bacteria ( Escherichia coli and Pseudomonas aeruginosa), yeasts ( Candida albicans and Saccharomyces cerevisiae) and molds ( Aspergillus niger and Penicillium citrinum). Complex 5 showed moderate antimicrobial activities against four bacteria, and two molds, while the ligand itself showed only modest antimicrobial activities against selected bacteria ( B. subtilis, E. coli and S. aureus). The molecular structures and antimicrobial activities of antimony(III) complexes were compared with those of bismuth(III) complexes in the same 15 group in the periodic table.