Electrochemical and optical recognition studies of anions using a multi-site ferrocene-based benzimidazolium receptor

A novel multi-site receptor 1 bearing four ferrocenyl arms comprising benzimidazolium moieties was synthesized and structurally characterized by IR, NMR, elemental analysis, mass spectra. Moreover, the structure of receptor 1 was confirmed by X-ray crystallography, it was clear that the cationic heterocyclic was interacted with PF6- through C-H<middle dot><middle dot><middle dot>F hydrogen bonds. Its electrochemical properties of sensing the various anions were investigated by cyclic voltammograms (CV) and differential pulse voltammetry (DPV), the receptor 1 displayed a significant cathodic shift for F(-)and OH-. The addition of F- and OH(-)to the solution of receptor 1 resulted in obvious absorption changes in the UV-Vis spectrum, showing that receptor 1 was an excellent sensor for these analytes (F-: LOD = 3.11 x 10(-6) M, LOQ = 1.03 x 10(-5) M, K-a = 5.83 x 10(5) M-1; and OH-: LOD = 1.36 x 10(-6) M, LOQ = 4.11 x 10(-5) M, K-a = 9.03 x 10(5) M-1). H-1 NMR titrations demonstrated that anion was recognized by receptor 1 through (C-H)(+)<middle dot><middle dot><middle dot>X- and C-H<middle dot><middle dot><middle dot>X hydrogen bonds, the binding process involve initial formation of hydrogen bond and followed by deprotonation.