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.