Unraveling cooperative interactions between complexed ions in dual-host strategy for cesium salt separation

The dual-host strategy offers a straightforward approach to ion separation, yet the nature of cooperative interactions between receptor-complexed cations and anions remains poorly understood. In this study, we utilize 18-crown-6 as a cation receptor and a tripodal hexaurea receptor L as an anion receptor to extract cesium salts (chloride, nitrate, carbonate, sulfate, and phosphate) from the solid phase into chloroform. Remarkably, Cs₃PO₄ exhibits the highest extraction efficiency, driven by strong cooperative interactions involving ion-dipole coordination between Cs⁺ and carbonyl (C=O) groups, as well as direct ion-pairing interactions between 18-crown-6-complexed Cs⁺ and hexaurea-bound PO₄ ^3-. Single-crystal structural analysis corroborates these interactions, shedding light on the underlying mechanisms and providing valuable guidance for the rational design of advanced dual-host systems for selective ion separation.