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

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 H-1 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. H-1 NMR titrations demonstrated that fluoride ion was recognized by receptors through (C-H)(+) center dot center dot center dot X- hydrogen bonds. (C) 2015 Elsevier B.V. All rights reserved.