Harnessing cooperative sorbate-sorbent adaptation in a flexible metal-organic framework for switchable hydrocarbon separation.

The pursuit of selective adsorption for separating molecules with similar shapes and interactions remains a formidable challenge. This work harnesses a powerful, previously unrecognized mechanism in a flexible metal-organic framework (Flex-Cd-MOF-3) to achieve switchable adsorption selectivity. Specifically, Flex-Cd-MOF-3, a descendant of Flex-Cd-MOF-2 with increased linker rigidity and functionalization, exhibits both local rearrangements and reversible framework expansion or shrinkage, showing phase-dependent propylene/propane selectivity. Considering propane, mutually beneficial conformational changes in the material and sorbate co-occur that are not possible with rigid propylene, reshaping the energy landscapes. These distinct interaction mechanisms, for otherwise very similar molecules, directly lead to pore swelling and shrinking at different pressures and phase switchable selectivity. An innovative modeling approach was developed that describes the full desorption pathway, explaining the relative binding energies and the sorbate-dependent mechanism of pore shrinkage. This work establishes cooperative sorbate-sorbent adaptation as a generalizable adsorption mechanism for achieving precise separation of similar molecules through distinct intermolecular interactions.