Designing Porous Materials to Resist Compression: Mechanical Reinforcement of a Zr-MOF with Structural Linkers

The performance of
metal–organic frameworks (MOFs) under
mechanical stress is an important consideration in the design, synthesis,
and application of MOF materials in both fundamental and industrial
settings. We herein demonstrate that the bulk modulus (K = −V dP/dV) of a 4,8-connected
Zr-based MOF, NU-901, comprised of Zr6O8 nodes
and tetratopic pyrene linkers, increases systematically upon postsynthetic
installation of a structural organic linker, 2,6-naphthalenedicarboxylic
acid (NDC), via solvent assisted linker incorporation. We calculated
the bulk modulus, a measure of resistance to hydrostatic compression,
of these modified NU-901 samples through in situ variable
powder X-ray diffraction pressure measurements collected using a synchrotron
source. As the amount of NDC incorporation into the NU-901 framework
increased, the lattice strength of the framework also increased. This
strategy of postsynthetic modification at the molecular level serves
as a promising blueprint to tune the bulk mechanical properties of
other MOFs by increasing the connnectivity of the secondary building
unit. Furthermore, we envision this method may allow for structural
reinforcement of other frameworks along one preferential axis or direction
dependent on the desired application.