Assessing the Stability of Metal-Organic Frameworks with Local Vibrational Mode Theory

The stability of metal-organic frameworks (MOFs) is crucial for their industrial applications, with metal-linker coordination bonds often being the weakest structural points. Here, we assessed the strength of these bonds in representative MOF series (UiO-66, MOF-5, and ZIFs) using local vibrational mode theory, which converts delocalized normal modes to local vibrational modes and associated local mode force constants, reflecting bond strength. Good agreement between the bond strengths obtained from local force constants and the corresponding experimental stability data was obtained, which in some cases was not reflected by the electron density at the bond critical points. The effects of linker functionalization were also analyzed, in which ortho-NH₂ substitutions on the linkers were found to weaken the adjacent coordination bonds via intramolecular hydrogen bonding. These findings establish a readily computable quantum-mechanical metric for evaluating bond strengths in MOFs, paving the way for accurate evaluation and prediction of MOF stability.