Lone-pair-electron Governed Gas-recognizable Flexibility in an Ultra-stable MOF for Boosting C3H6/C3H8 Separation and Its Aqueous Scalable Synthesis

The separation of propylene (C ₃ H ₆ ) from propane (C ₃ H ₈ ) constitutes one of the most energy-demanding processes in the petrochemical industry, a consequence of their nearly identical molecular dimensions and physicochemical properties. Metal-organic frameworks (MOFs) have emerged as a promising adsorptive alternative to traditional distillation. Among these, flexible MOFs, which undergo selective guest-induced structural transformations, offer a unique 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 organic pillar ligand, specifically replacing pyridyl termini 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 architecture. The resulting material, NJU-Bai5-bib, exhibits a well-defined, selective gate-opening transition that is triggered preferentially by C ₃ H ₆ 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 fundamental excellence in guest-specific recognition but also considerable potential for practical, energy-efficient propylene purification.