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-naphthalenedi-carboxylic 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.