Metal-Regulated Flexibility Engineering of Metal–Organic Frameworks for C ₂ H ₂ /CO ₂ Separation

The rational design of adsorbents with optimal structural features for C2H2/CO2 separation remains challenging because of their similar molecular features. Herein, we synthesized a series of isostructural flexible MOFs (M-bz, M = Co, Ni, and Zn, bz = 5-(3,5-dimethyl-1H-pyrazol-4-yl) isophthalic acid), where the structural flexibility and pore architectures are regulated by the metal nodes. They display selective adsorption of C2H2 over CO2, with Co-bz demonstrating the highest C2H2/CO2 selectivity and uptake ratio of 5.36 and 2.71, respectively. The separation capability was validated by multicomponent breakthrough measurements. This has been attributed to its optimal flexibility and pore surface chemistry, providing multiple hydro-gen bonds (C–H···N and C–H···O) and C–H···π interactions for enhanced C2H2 adsorption affinity.