Discriminatory Gate-Opening Effect in a Flexible Metal-Organic Framework for Inverse CO₂/C₂H₂ Separation

Considering the significant application of acetylene (C2H2) in the manufacturing and petrochemical industries, the selective capture of impurity carbon dioxide (CO2) is a crucial task and an enduring challenge. Here, a flexible metal-organic framework (Zn-DPNA) accompanied by a conformation change of the Me2NH2+ ions in the framework is reported. The solvate-free framework provides a stepped adsorption isotherm and large hysteresis for C2H2, but type-I adsorption for CO2. Owing to their uptakes difference before gate-opening pressure, Zn-DPNA demonstrated favorable inverse CO2/C2H2 separation. According to molecular simulation, the higher adsorption enthalpy of CO2 (43.1 kJ mol(-1)) is due to strong electrostatic interactions with Me2NH2+ ions, which lock the hydrogen-bond network and narrow pores. Furthermore, the density contours and electrostatic potential verifies the middle of the cage in the large pore favors C2H2 and repels CO2, leading to the expansion of the narrow pore and further diffusion of C2H2. These results provide a new strategy that optimizes the desired dynamic behavior for one-step purification of C2H2.