Ion-Pair Recognition by a Heteroditopic Triazole-Containing Receptor

A new heteroditopic calix[4]diquinone triazole containing receptor capable of recognising both cations and anions through Lewis base and C-H hydrogen-bonding modes, respectively, of the triazole motif has been prepared. This ion-pair receptor cooperatively binds halide/monovalent-cation combinations in an aqueous mixture, with selectivity trends being established by H-1 NMR and UV/Vis spectroscopy. Cation binding by the calix[4]diquinone oxygen and triazole nitrogen donors enhances the strength of the halide complexation at the isophthalamide recognition site of the receptor. Conversely, anions bound in the receptors isophthalamide cavity enhance cation recognition. H-1 NMR investigations in solution suggest that the receptors triazole motifs are capable of coordinating simultaneously to both cation and anion guest species. Solid-state X-ray crystallographic structural analysis of a variety of receptor ion-pair adducts further demonstrates the dual cationanion binding role of the triazole group.