The effect of short alkane bridges in stability of bisbenzimidazole-2-ylidene silver(I) complexes: synthesis, crystal structure and antibacterial activity

Three bisbenzimidazolium salts, 3,3-(alkane-1,n-diyl)bisbenzylbenzimidazolium dibromide/dihexafluorophosphate (1a/b–3a/b) (where alkane = ethane, propane or butane and n = 2, 3, or 4), were synthesized. The bromide salts were subsequently used as precursors to prepare their respective Ag(I)-NHC complexes via in situ deprotonation method. The successful formation of all bisbenzimidazolium salts and complexes were proved by elemental analysis, 1H-NMR, 13C-NMR and FT-IR analyses. From single-crystal X-ray diffraction analyses, 4 has been established as a binuclear complex with the molecule arranged as in trans-conformation. Salts 1b–3b and Ag(I)-NHC complexes 4–6 were then screened for their antibacterial potential against E. coli (ATCC 25922) and S. aureus (ATCC 12600). All the bisbenzimidazolium salts do not show any activity against both bacteria while 4 exhibits the highest activity against both bacteria in all methods followed by 5 and 6.