Acetylene-Triggered Gate-Opening Behavior in a Stable Rigid-Flexible MOF for Efficient C2H2/CO2 Separation.

High-purity acetylene (C2H2) is indispensable in the chemical industry. However, C2H2 produced via the calcium carbide process contains trace CO2 impurities, necessitating purification. Due to their comparable molecular dimensions (3.3 × 3.3 × 5.7 Å3 for C2H2 vs 3.2 × 3.3 × 5.4 Å3 for CO2), achieving effective separation remains a challenge. For the first time, this work achieves efficient C2H2/CO2 separation in an ultra-stable metal-organic framework (MOF) featuring a synergistic rigid-flexible structure, characterized by a 2-fold interpenetrating MOF that incorporates an unprecedented [Zn4N9]n chain. The rigid molecular chains ensure stability, as the structure is retained after immersion in strong acidic environments for one month. The 2-fold interpenetration architecture imparts controlled structural flexibility to the framework, triggering a stimuli-responsive gate-opening phenomenon upon C2H2 adsorption. This dynamic structural transformation induces a significant pore environment modulation, as quantified by the expansion of the pore limiting diameter (PLD) from 3.09 to 3.34 Å. The precisely tuned aperture demonstrates exceptional molecular sieving capabilities, permitting selective C2H2 permeation while effectively rejecting CO2 molecules due to their differential kinetic diameters. Integrated analysis of gas adsorption isotherms, theoretical calculations, breakthrough experiments, and stability assessments synergistically confirm the structural robustness and selective separation efficacy of this interpenetrated framework.