Enhancing selectivity of cation exchange with anion receptors.

We introduce a new supramolecular strategy where an anion receptor modifies the selectivity ligands for cations. This is demonstrated by combining the classic anion receptor calix[4]pyrrole (C4P) and a phenolic ligand, which leads to remarkable enhancement in selectivity for Cs+ over Na+. Crystal structures and molecular simulations confirmed the persistent formation of ion-pair C4P-Cs+-phenolate complexes, while the smaller Na+ ion cannot efficiently interact.