Gate-Opening Effect in a Flexible Metal-Organic Framework for Sieving Acetylene

Adsorptive separation employing porous materials is one of the most promising alternative technologies for C₂H₂ purification due to its energy-efficient and environmentally friendly advantages. Herein, we present the design and synthesis of a dicopper-paddle-wheel-based metal-organic framework (termed JNU-5-Me) with a carboxylate-azolate organic linker. The use of such a linker results in the axial positions of the dicopper paddle wheels being occupied by azolates, and therefore, a much-improved chemical stability of the framework structure. JNU-5-Me shows negligible adsorption of C₂H₄, C₂H₆, and CO₂ at 1.0 bar and 298 K, while a gate-opening effect for C₂H₂ and a large C₂H₂ adsorption (4.7 mmol g^-1) at 1.0 bar and 298 K. Dynamic breakthrough studies on JNU-5-Me demonstrate its excellent C₂H₂ separation performance from C₂H₂/CO₂ (50/50, v/v) and C₂H₂/CO₂/C₂H₄/C₂H₆ (70/10/10/10, v/v/v/v) mixtures. Additionally, in-situ infrared spectroscopy and Grand canonical Monte Carlo (GCMC) simulation reveal that the carboxylate oxygens and methyl groups on the framework are involved in the strong binding of C₂H₂, which may be attributed to the gate-opening effect of JNU-5-Me.