Calix[4]pyrrole: An Old yet New Ion‐Pair Receptor

Abstract

Ditopic cation–anion binding is revealed by solid-state studies of the anion-recognition behavior of the calix[4]pyrrole unit. Anion binding causes an electron-rich conelike cavity to be formed that can then bind large polarizable cations. Furthermore, complexation of calix[4]pyrrole with cesium carbonate results in dimerization, in which a single anion bridges two calix[4]pyrroles (see the crystal structure of the Cs2CO3 complex).