Discriminatory Gate-Opening Effect in a Flexible Metal-Organic Framework for Inverse CO 2 /C 2 H 2 Separation.

Considering the significant application of acetylene (C 2 H 2 ) in the manufacturing and petrochemical industries, the selective capture of impurity carbon dioxide (CO 2 ) is a crucial task and an enduring challenge. Here, a flexible metal-organic framework (Zn-DPNA) accompanied by a conformation change of the Me 2 NH 2 + ions in the framework is reported. The solvate-free framework provides a stepped adsorption isotherm and large hysteresis for C 2 H 2 , but type-I adsorption for CO 2 . Owing to their uptakes difference before gate-opening pressure, Zn-DPNA demonstrated favorable inverse CO 2 /C 2 H 2 separation. According to molecular simulation, the higher adsorption enthalpy of CO 2 (43.1 kJ mol -1 ) is due to strong electrostatic interactions with Me 2 NH 2 + 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 C 2 H 2 and repels CO 2 , leading to the expansion of the narrow pore and further diffusion of C 2 H 2 . These results provide a new strategy that optimizes the desired dynamic behavior for one-step purification of C 2 H 2 .