By combining the classic anion receptor calixpyrrole (C4P) and a phenolic ligand, a remarkable enhancement in selectivity was found for Cs+ over Na+, which was confirmed by crystal structures and ab initio molecular dynamics (AIMD), which showed the formation of ion-pair C4P-Cs+–phenolate complexes, while the smaller Na+ ion cannot effectively interact with all four pyrrole rings.
Significance and Impact
This study introduces a new supramolecular strategy of using anion receptors to influence the selectivity of a cation receptor without modifying its structure.
- The results of liquid– liquid extraction experiments demonstrate a dramatic enhancement of Cs+ selectivity from alkaline solution when both phenol cation exchanger and C4P are present in a water-immiscible organic solvent.
- This supramolecular concept was structurally validated with crystal structures showing the expected role of C4P as ion-pair receptor.
- DFT and AIMD simulations further support these findings, while showing poor structural organization of the binding site and low affinity for Na+.
Neil J. Williams, Santanu Roy, Campbell O. Reynolds, Radu Custelcean, Vyacheslav S. Bryantsev and Bruce A. Moyer, Chem. Commun., 2019, 55, 3590, DOI: 10.1039/c9cc00287a