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, H-1-NMR, C-13-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.