Mapping the Complete Reaction Energy Landscape of a Metal-Organic Framework Phase Transformation

Crystalline materials undergo valuablephase transformations, andthe energetic processes that underlie these transformations can befully characterized through a combination of thermodynamic and kineticstudies. Here, we report the first complete reaction energy landscapeof metal-organic framework (MOF) interpenetration, specificallyin the phase transformation of NU-1200 to its doubly interpenetratedcounterpart, STA-26. We characterized the thermodynamics of this phasetransformation by pairing experiments with density functional theory(DFT) calculations. This analysis revealed that factors such as theincrease in crystal density likely drive Zr- and Hf-NU-1200 to STA-26interpenetration, while other chemical interactions such as stericrepulsions prevent Th-NU-1200 from interpenetrating. Using time-resolved in situ X-ray diffraction, we monitored phase transformationreaction profiles and extracted quantitative kinetic information usingthe Avrami-Erofe'ev model. As a result, we obtained activationenergies for the Zr- and Hf-NU-1200 transformations to Zr- and Hf-STA-26,respectively, revealing slower phase change kinetics for MOFs withstronger bonds. Finally, we paired the kinetic data with experimentalobservations to classify the mechanistic model of this phase transformationas partial dissolution. We anticipate that this thermodynamic, kinetic,and mechanistic understanding will broadly inform further studieson the energetics of crystallization.