Phonons and Adsorption-Induced Deformations in ZIFs: Is It Really a Gate Opening?

Abstract : We report a microscopic model of the phonon-adsorption correlations in flexible metal−organic framework materials. We analyze the mechanism of the gate opening deformation using the notion of coupled phonon- and adsorption-induced structural transformation. Using the ZIF-8 structure as an example, we perform an analysis of transformation-related, low-frequency phonon modes of the framework. On the basis of structure-related quantities such as pore limiting diameter, void fraction, and adsorption uptake, we determine the conditions which lead to the gate opening transformation in ZIF-8. Energetic landscape of the deformation process is analyzed using grand thermodynamic potential of adsorption. We generalize our conclusions to other flexible ZIF structures with the same topology.