Zero- to One-Dimensional Transformation in a Highly Porous Metal–Organic Framework to Enhance Physicochemical Properties

The dynamic behaviors of metal-organic frameworks (MOFs) continue to expand the accessible architectures and properties within this material class. However, the dynamic behaviors that can be studied in MOFs are limited to the transitions, preserving their high crystallinity. For this reason, their significant structural changes involving coordination bond breakage and rearrangement remain largely underexplored. Herein, we report a three-step single-crystal-to-single-crystal (SCSC) phase transition in a new cerium-based MOF, HKU-9 [Ce₂PET(DMF)₂(H₂O)₂], transforming zero-dimensional (0D) secondary building units (SBUs) into one-dimensional (1D) chain SBUs in HKU-90 [Ce₂(μ-H₂O)PET(H₂O)₂]. Single-crystal X-ray diffraction studies unambiguously delineate the structural evolution at each stage of this multistep transition, revealing multiple coordination bond dissociations/associations and a significant lattice contraction─all while preserving single-crystal integrity. This dimensional transformation endows HKU-90 with enhanced chemical stability (pH 1-10) and a record-high Brunauer-Emmett-Teller (BET) surface area of 2660 m² g^-1 among reported Ce-based MOFs. Further, HKU-90 exhibits exceptional gas sorption performance, with one of the highest reported C₂H₂ storage capacities (184 cc g^-1 at 273 K, 1 bar) and outstanding C₂H₂/CO₂ selectivity (2.16) under these conditions. Notably, the formation of 1D chain SBUs, a structural motif found in many high-performance MOFs, highlights the potential of using the solid-state fusion of multinuclear metal clusters to tailor the properties of the framework.