Effect of low frequency phonons on structural properties of ZIFs with SOD topology

The structural transformations of periodic structures are very often initiated by the dynamical fluctuation of the equilibrium structure. The natural mechanical excitations in crystals are called phonons. If the energy of these fluctuations is low, they can easily be transformed into static deformations which define new structural properties of the materials. This is the case in so called gate opening transformations which modify the structure and the adsorptive properties of porous solids. Using the example of three SOD-type zeolitic imidazolate frameworks (ZIFs) containing linker molecules with different substituents, we show that analysis of low-frequency phonons obtained from density-functional theory (DFT) calculations allows one to model the observed gate opening and to understand the microscopic mechanism of this structural transformation.