Guest Polarizability Directed Molecular 'Freezing' within Non-metal Porous Salt Frameworks.

Abstract

Isoreticular non-metal salt frameworks with permanent porosity have emerged recently as a fantastic platform for molecular separation, but the underlying guest-framework interactions within their charge-separated ionic channels remain to be explored. Here, we report the first case of guest polarizability-directed molecular 'freezing' of noble gas occurring within a non-metal porous organic ammonium framework, which bears well-organized, high-density chloride anions as nodes. Notably, the framework exhibits a distinctive, thermally-independent commensurate adsorption towards highly polarizable Xe, while traditional thermodynamic adsorption behaviors are observed for Kr with lower polarizability. A remarkable Xe adsorption capacity of 1.47 mmol/g and a record-high separation factor of 10.2 are thus achieved in dynamic Xe/Kr separation under ambient conditions. The practical potential for realistic Xe/Kr separation from the off-gas of used nuclear fuel (UNF) reprocessing is demonstrated. Theoretical calculations identify the presence of multiple strong Xe···Cl interactions as the driving force within the size-matching ionic channels of the salt framework.