Lone-pair-electron-governed gas-recognizable flexibility in a stable MOF for boosting C₃H₆/C₃H₈ separation via...

The separation of propylene from propane constitutes one of the most energy-demanding processes in the petrochemical industry due to their similar molecular dimensions and physicochemical properties. Flexible MOFs, which undergo selective guest-induced structural transformations, offer an alternative mechanism to amplify subtle molecular differences into distinct adsorption behaviors. Nevertheless, the precise molecular-level modulation of framework flexibility to elicit a selective response to one specific gas over another remains a great challenge. This study confronts this challenge through the rational structural evolution of a hydrolytically stable, pillar-layered Cu-MOF, NJU-Bai5. Our strategy involves the strategic engineering of the pillar ligand, specifically replacing pyridyl with imidazolyl groups. This modification introduces accessible nitrogen lone-pair-electrons, which function as molecular anchors capable of forming selective interactions with hydrogen-bonding donors possessing higher acidity. These interactions, in turn, drive a gas-recognizable flexibility of the framework. The resulting material, NJU-Bai5-bib, exhibits a well-defined, selective gate-opening transition triggered preferentially by C₃H₆ at low pressures. This specific response enables the framework to achieve highly selective propylene/propane separation under ambient conditions. Furthermore, by inheriting exceptional hydrolytic stability from its progenitor and featuring a scalable, aqueous synthesis, NJU-Bai5-bib demonstrates not only excellence in guest-specific recognition but also considerable potential for practical, energy-efficient propylene purification.