Discriminatory Gate-Opening Effect in a Flexible Metal-Organic Framework for Inverse CO₂ /C₂ H₂ Separation

Considering the significant application of acetylene (C₂ H₂ ) 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 Me₂ NH₂ ⁺ ions in the framework is reported. The solvate-free framework provides a stepped adsorption isotherm and large hysteresis for C₂ H₂ , but type-I adsorption for CO₂ . Owing to their uptakes difference before gate-opening pressure, Zn-DPNA demonstrated favorable inverse CO₂ /C₂ H₂ separation. According to molecular simulation, the higher adsorption enthalpy of CO₂ (43.1 kJ mol^-1 ) is due to strong electrostatic interactions with Me₂ NH₂ ⁺ 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 C₂ H₂ and repels CO₂ , leading to the expansion of the narrow pore and further diffusion of C₂ H₂ . These results provide a new strategy that optimizes the desired dynamic behavior for one-step purification of C₂ H₂ .