Tailoring Pore Environments in Metal-Organic Frameworks for Efficient C2H2/CO2 and C2H2/C2H4 Separations.

The efficient separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) is of significant industrial importance but remains highly challenging due to their similar physicochemical properties. In this study, three isostructural metal-organic frameworks, [Co4(µ4-SO4)2(tpim)2(L)2] (tpim = 2,4,5-tri(4-pyridyl)-imidazole, L = dicarboxylate; termed as Co4-L), are constructed from sulfate-capped Co4 clusters extended by N-rich tpim linkers and different-sized dicarboxylate ligands. Among them, the Co₄-1,4-ndc framework, incorporating 1,4-naphthalenedicarboxylic acid (1,4-ndc), offers optimal pore confinement that promotes host-guest interactions between C₂H₂ molecules and framework. This material exhibits high C₂H₂ capture capacities of 4.30 and 3.40 mmol g-¹ from equimolar C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures, respectively. Theoretical simulations reveal that the enhanced selectivity arises from multiple cooperative hydrogen-bonding interactions between C₂H₂ and the framework Co₄-1,4-ndc, generating strong and preferential binding sites. This study highlights the role of pore-environment engineering of metal-organic frameworks (MOFs) for selective C₂H₂ separation, providing a foundation for the development of advanced adsorbents in industrial gas purification.