👤 Rajini Brammananth

Five mixed thiolatobismuth(III) complexes [BiPh(5‐MMTD)2{4‐MMT(H)}] (1), [Bi(1‐MMTZ)2{(PYM)(PYM(H))2}] (2), [Bi(MBT)2(5‐MMTD)] (3), [Bi(4‐BrMTD)3{2‐MMI(H)}] (4) and [Bi(1‐MMTZ)2{1‐MMTZ(H)}(2‐MMI){2‐MMI(H)2}] (5) were synthesised from imidazole‐, thiazole‐, thiadiazole‐, triazole‐, tetrazole‐ and pyrimidine‐based heterocyclic thiones. Four of these complexes 1–4 were synthesized from BiPh3, while complex 5 was obtained from Bi[4‐(MeO)Ph]3. Complexes 1–5 were structurally characterised by XRD. Evaluation of the antibacterial properties against Mycobacterium smegmatis, Staphylococcus aureus, Methicillin‐resistant S. aureus (MRSA), Vancomycin‐resistant Enterococcus (VRE), Enterococcus faecalis and Escherichia coli showed that mixed thiolato complexes containing the anionic thiazole‐based ligands MBT and 4‐BrMTD are most effective. The mixed thiolato complexes [Bi(MBT)2(5‐MMTD)] (3) having thiazole‐ and thiadiazole‐ and [Bi(4‐BrMBT)3{2‐MMI(H)}] (4) containing thiazole‐ and imidazole‐based ligands proved to be more efficient, with low minimum inhibitory concentrations of 1.73 and 3.45 µm for 3 against VRE and E. faecalis, respectively, and 2.20 µm for 4 against M. smegmatis and E. faecalis. All complexes showed little or no toxicity towards mammalian COS‐7 cell lines at 20 µg mL–1. Show less

AbstractHomo‐ and heteroleptic bismuth thiolato complexes have been synthesised and characterised from biologically relevant tetrazole‐, imidazole‐, thiadiazole‐ and thiazole‐based heterocyclic thiones (thiols): 1‐methyl‐1H‐tetrazole‐5‐thiol (1‐MMTZ(H)); 4‐methyl‐4H‐1,2,4‐triazole‐3‐thiol (4‐MTT(H)); 1‐methyl‐1H‐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 BiPh3 with 1‐MMTZ(H) produced the rare BiV thiolato complex [BiPh(1‐MMTZ)4], 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 μM for [BiPh(4‐MTT)2{4‐MTT(H)}2] against VRE, and 1.33 μM for [BiPh(1‐MMTZ)2{1‐MMTZ(H)}2] against M. smegmatis and S. aureus. Tris‐thiolato BiIII complexes were least effective overall. All complexes showed little or no toxicity towards mammalian COS‐7 cells at 20 μg mL−1. Show less