Anion receptors of N-ferrocenylmethylene-substituted bis-imidazolium salts linked by xylene spacers

Abstract

A series of xylyl (ortho, meta, and para) linked N-ferrocenylmethylene-substituted bis-imidazolium salts (3a–3c) and bis-benzimidazolium salts (4a–4c) were synthesized and structurally characterized. Their binding properties for anions were investigated by electrochemistry and 1H NMR spectroscopy. The structure of 3b, 3c, 4a and 4b were confirmed by X-ray crystallography. As expected, all salts were good electrochemistry-signaling receptors for several anions (F−, AcO−, HSO4−, Cl−, Br− and I−), that in one receptor the imidazolium/benzimidazolium units offer binding sites for anion and the ferrocenyl units offer electrochemistry response sites. Furthermore, the results showed that they were highly selective and sensitive to F− and receptors 3b and 4b featuring a meta-xylene spacer were more effective receptors for F− compared to receptors linked by an orth or a para-xylene spacer. 1H NMR titrations demonstrated that fluoride ion was recognized by receptors through (C–H)+···X− hydrogen bonds.