Homo- and heteroleptic bismuth(III/V) thiolates from N-heterocyclic thiones: synthesis, structure and anti-microbial activity

Homo- and heteroleptic bismuth thiolato complexes have been synthesised and characterised from biolog,ically relevant tetrazole-, imidazole-, thiadiazole- and thia-zole- based heterocyclic thiones (thiols): 1-methyl-1 H-tetra-zole- 5-thiol (1-MMTZ(H)); 4-methyl-4 H-1,2,4-triazole-3-thiol (4-MTT(H)); 1-methyl-1 H-imidazole-2-thiol (2-MMI(H)); 5- methyl-1,3,4-thiadiazole-2-thiol (5-MMTD(H)); 1,3,4-thiadia-zole- 2-dithiol (2,5-DMTD(H)₂); and 4-(4-bromophenyl)thia-zole- 2-thiol (4-BrMTD(H)). Reaction of BiPh₃ with 1-MMTZ(H,) produced the rare BiV thiolato complex [BiPh(1-MMTZ,)_{4,/inf>], which undergoes reduction in DMSO to give [BiPh(1- MMTZ)2}{(1-MMTZ(H)}₂]. Reactions with PhBiCl₂ or BiPh₃ generally produced monophenylbismuth thiolates, [BiPh(SR)₂]. The crystal structures of [BiPh(1-MMTZ)₂{1-MMTZ(H)}₂], [BiPh(5-MMTD)₂], [BiPh{2,5-DMTD(H)}₂(Me₂C=O)] and [Bi(4- BrMTD)₃] were obtained. Evaluation of the bactericidal properties against M. smegmatis, S. aureus, MRSA, VRE, E. faecalis and E. coli showed complexes containing the anionic ligands 1- MMTZ, 4-MTT and 4-BrMTD to be most effective. The dithiolato dithione complexes [BiPh(4-MTT)₂{4-MTT(H)}₂] and [BiPh(1-MMTZ)₂{1-MMTZ(H)}₂] were most effective against all the bacteria: MICs 0.34 m m for [BiPh(4-MTT)₂ {4-MTT(H)}₂] against VRE, and 1.33 mm for [BiPh(1-MMTZ)₂{1-MMTZ(H)}₂] against M. smegmatis and S. aureus. Tris-thiolato Bi^III complexes were least effective overall. All complexes showed little or no toxicity towards mammalian COS-7 cells at 20 μgmL^-1.