Temperature-Dependent Gate-Opening Behavior and C2H2/CO2 and C2H2/C2H4 Separation in a 4-Fold Interpenetrated Flexible MOF.

The efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) is critical for producing high-purity chemical feedstocks but remains challenging due to their similar physicochemical properties. The development of functional metal-organic frameworks (MOFs) featuring superior selectivity for both C2H2/CO2 and C2H2/C2H4 mixtures is quite necessary. Herein, we synthesized a novel 4-fold interpenetrated flexible MOF (Zn-MOF-α) that exhibits a reversible solid-state structural transformation upon guest removal/uptake. After activation, Zn-MOF-α (featuring 2D cavities) converts to Zn-MOF-β (with 0D voids) accompanied by the rotation of the organic linkers and the contraction of interstitial spaces. Notably, Zn-MOF-β features unique temperature-dependent gate-opening effects toward C2 gases. At 298 K and 1 bar, it exhibits high selectivities of 15.7 for equimolar C2H2/CO2 and 15.2 for equimolar C2H2/C2H4, outperforming many previously reported MOFs. Dynamic breakthrough experiments further confirm its excellent separation performance for binary mixtures (C2H2/CO2 and C2H2/C2H4) under various conditions, demonstrating efficient recovery of high-purity C2H2 with remarkable cyclic stability. This work provides a promising adsorbent for challenging gas separation and offers a rational design strategy for advanced MOF materials.