Acyclic ferrocene-based imidazolium salts as multi-site anion receptors

Several novel acyclic multi-site receptors comprising of imidazolium moieties were synthesized and structurally characterized. All of these compounds were characterized through 1H NMR, 13C NMR, MS and IR, elemental analysis. The crystal structures of 1,4-bis(1-ferrocenylmethylimidazoliumylethoxy)-benzene hexafluorophosphate (1) and 1,3-bis(1-ferrocenylmethylimidazoliumylethoxy)-benzene hexafluorophosphate (2) were confirmed by X-ray crystallography, it was clear that molecules were linked by C–H⋯F hydrogen bonds interactions between PF6− and cations. The anion binding studies were investigated by electrochemistry and 1H NMR spectroscopy. Electrochemical behaviors indicated that all the receptors displayed unique electrochemical sensing property for F− in CH3CN. 1H NMR titrations demonstrated that all the receptors have good fluoride binding ability in DMSO-d6 through (C–H)+⋯X− hydrogen bonds. The flexible receptors 1 and 2 exhibited higher affinity toward anion than the rigid receptors 3 and 4.