Host–Guest Interaction Modulation in Porous Coordination Polymers for Inverse Selective CO₂/C₂H₂ Separation

Controlling gas sorption by simple pore modification is important in molecular recognition and industrial separation processes. In particular, it is challenging to realize the inverse selectivity, which reduces the adsorption of a high-affinity gas and increases the adsorption of a low-affinity gas. Herein, an “opposite action” strategy is demonstrated for boosting CO₂/C₂H₂ selectivity in porous coordination polymers (PCPs). A precise steric design of channel pores using an amino group as an additional interacting site enabled the synergetic increase in CO₂ adsorption while suppressing the C₂H₂ adsorption. Based on this strategy, two new ultramicroporous PCP physisorbents that are isostructural were synthesised. They exhibited the highest CO₂ uptake and CO₂/C₂H₂ volume uptake ratio at 298 K. Origin of this specific selectivity was verified by detailed density functional theory calculations. The breakthrough separation performances with remarkable stability and recyclability of both the PCPs render them relevant materials for C₂H₂ purification from CO₂/C₂H₂ mixtures.