Water cluster triggered vitrification in HKUST ‐1 MOF crystal under pressure

Metal–organic framework (MOF) glasses feature several unique dynamic and thermodynamic properties that differentiate them from their crystalline counterparts. However, the formation of MOF glasses usually requires the melt‐quenching of molten MOFs from relatively high temperatures. In practice, this approach is quite limited because most MOFs decompose below their melting points. Herein, we demonstrate a direct crystal‐to‐glass transition in HKUST‐1 MOF that has been achieved at room temperature and a relatively low pressure of <1.0 GPa. The dramatic fall in the required pressure is shown to arise from the aggregation of coordinated polar water molecules to form water clusters that exhibit a pulling effect on the Cu–O (ligand) bonds. Meanwhile, the departed fragment gets flipped unfavorably to prevent further regeneration of the bond. Accordingly, a grain boundary‐free continuous porous framework in the glassy state is successfully formed and can be fabricated into membranes. Given their unique microporosity and grain boundary‐free characteristics, such MOF glass membranes present new opportunities for chemical separation (both gases and liquids), electrochemistry, and catalysts, promising a new platform for MOF glasses.