Metal–Organic Frameworks with a Crystal System Switch for Optical Tuning
Abstract
Metal–organic frameworks (MOFs) that undergo structural transformations, such as crystal systems or space group changes (CSC/SGC), occupy a unique niche among functional porous materials. For such MOFs, we demonstrate how the CSC/SGC processes govern their electronic and optical properties in a reversible/irreversible manner. First, data analysis of 67 MOFs with crystallographically confirms that CSC/SGC reveals an equal probability of symmetry increasing/decreasing during CSC/SGC. Second, the analysis uncovers a counterintuitive yet weak correlation between the CSC/SGC process and both the MOF ligand length and the presence of hinge bonding. Finally, numerical calculations show a significant transformation in the electron density of states and refractive indices upon CSC/SGC. Our findings, thereby, pave the way for predicting and utilizing such MOFs as functional porous materials for optics, next to their established role in chemistry.