Order-to-Disorder Transition in a Zirconium-Based Metal–Organic Framework

DUT-67 is a Zr-based metal–organic framework (MOF) that incorporates thiophene dicarboxylic acid linkers. In this study, we observed that DUT-67 underwent a striking structural order–disorder transition upon a dynamic heating process. We established a correlation between thermal responses and structural changes in DUT-67 during heating through both calorimetric analysis and structural characterization at various length scales. It was discovered that the chemical integrity of the DUT-67 linkers remained intact during heating. The morphology of DUT-67 was preserved after structural changes, while 50% of its porosity was retained, increasing the apparent density of the framework. The chemical changes caused by the heating were directly related to desolvation. The atomic pair distribution function analyses revealed that the structural disordering process occurred during heating. This was supported by a notable decrease in correlations between neighboring clusters, indicating a loss of structural order. The structural reordering in DUT-67 was found to involve multiple thermally induced phase transitions and then amorphization. The amorphous form of DUT-67 preserved both the high porosity and the functionality observed in its original crystalline state. This study implies that it is possible to find inherently unstable MOF structures for order–disorder engineering for creating new functionalities.