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 biologically relevant tetrazole‐, imidazole‐, thiadiazole‐ and thiazole‐based heterocyclic thiones (thiols): 1‐methyl‐1 H ‐tetrazole‐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‐thiadiazole‐2‐dithiol (2,5‐DMTD(H) 2 ); and 4‐(4‐bromophenyl)thiazole‐2‐thiol (4‐BrMTD(H)). Reaction of BiPh 3 with 1‐MMTZ(H) produced the rare Bi V thiolato complex [BiPh(1‐MMTZ) 4 ], which undergoes reduction in DMSO to give [BiPh(1‐MMTZ) 2 {(1‐MMTZ(H)} 2 ]. Reactions with PhBiCl 2 or BiPh 3 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 (Me 2 CO)] 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 μ M for [BiPh(4‐MTT) 2 {4‐MTT(H)} 2 ] against VRE, and 1.33 μ M 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 μg mL −1 .