Controlled Demolition and Reconstruction of Imidazolate and Carboxylate Metal–Organic Frameworks by Acid Gas Exposure and Linker Treatment

The metal-linker coordination bond
in metal–organic frameworks
(MOFs) can be unstable in humid and acid gas environments, leading
to loss of crystallinity and porosity. This degradation is not necessarily
irreversible; solvent-assisted crystal redemption (“SACRed”)
has been shown to recover the physical and chemical properties of
ZIF-8 exposed to humid SO2. This approach can also be useful
in creating mixed-linker materials that might be challenging to produce
via de novo synthesis. Here, we expand more generally
the concept of controlled degradation of a MOF with acid gas, followed
by treatment with a fresh linker solution, to the use of different
template MOFs (ZIFs, UiO-66, and UiO-67) and acid gases (SO2 and NO2 in dry and humid conditions). Significant losses
in porosity and crystallinity along with structural changes (acid
gas-linker complexes and linker functionalizations) are observed in
the acid gas-exposed MOF templates, and SACRed is shown to reconstruct
these partially demolished MOFs with a high degree of structural recovery.
Detailed structural and spectroscopic characterizations of the controlled
degradation and subsequent recovery are presented and analyzed. These
findings indicate the generality of controlled degradation and reconstruction
as a means for linker replacement in a wider variety of MOFs and also
create the potential for linker substitutions (with non-native linkers)
to obtain new hybrid MOFs.