Systematic Regulation of C₂H₂/CO₂ Separation by 3p-Block Open Metal Sites in a Robust Metal–Organic Framework Platform

The separation of a mixture of C₂H₂ and CO₂ is a great challenge due to their similar molecular sizes and shapes. Al-based metal–organic frameworks (Al-MOFs) have great promise for gas separation applications due to their light weight, high stability, and low cost. However, the cultivation of suitable Al-MOF single crystals is extremely difficult and has limited their explorations up to now. Since In, Ga, and Al are all 3p-block metal elements, a systematic application of the periodic law to investigate 3p-MOFs will undoubtedly help in the understanding and development of worthy Al-MOF materials. Herein, we report the design of a robust 3p metal–organic framework platform (SNNU-150) and the systematic regulation of C₂H₂/CO₂ separation by open 3p-block metal sites. X-ray single-crystal diffraction analysis reveals that SNNU-150 is a 3,6-connected 3D framework consisting of [M₃O­(COO)₆] trinuclear secondary building units (SBUs) and tritopic nitrilotribenzoate (NTB) linkers. Small {[M₃O­(COO)₆]₄(NTB)₆} tetrahedral cages and extra-large {[M₃O­(COO)₆]₁₀(NTB)₁₄} polyhedral cages connect with each other to generate a hierarchically porous architecture. These 3p-MOFs present very high water, thermal, and chemical stability, especially for SNNU-150-Al, which can maintain its framework at 85 °C in water for 24 h and in a room-temperature environment for more than 30 days. IAST calculations, breakthrough experiments, and GCMC simulations all show that SNNU-150 MOFs have top-level C₂H₂/CO₂ separation performance and follow the order Al-MOF > Ga-MOF > In-MOF.