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 ų for C₂H₂ vs 3.2 × 3.3 × 5.4 ų 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.