Cyclobutanedicarboxylate Metal-Organic Frameworks as a Platform for Dramatic Amplification of Pore Partition Effect

Ultrafinetuning of MOF structures at subangstrom or picometerlevels can help improve separation selectivity for gases with subtledifferences. However, for MOFs with a large enough pore size, theeffect from ultrafine tuning on sorption can be muted. Here we showan integrative strategy that couples extreme pore compression withultrafine pore tuning. This strategy is made possible by unique combinationof two features of the partitioned acs (pacs) platform: multimodular framework and exceptional tolerance towardisoreticular replacement. Specifically, we use one module (ligand1, L1) to shrink the pore size to an extreme minimum on pacs. A compression ratio of about 30% was achieved (based on the unitcell c/a ratio) from prototypical1,4-benzenedicarboxylate-pacs to trans-1,3-cyclobutanedicarboxylate-pacs. This is followedby using another module (ligand 2, L2) for ultrafine pore tuning (<3%compression). This L1-L2 strategy increases the C2H2/CO2 selectivity from 2.6 to 20.8 and givesrise to an excellent experimental breakthrough performance. As theshortest cyclic dicarboxylate that mimics p-benzene-basedmoieties using a bioisosteric (BIS) strategy on pacs, trans-1,3-cyclobutanedicarboxylate offers newopportunities in MOF chemistry.