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.