Improving the Mechanical Stability of Metal–Organic Frameworks Using Chemical Caryatids

Metal–organic
frameworks (MOFs) have emerged as versatile
materials for applications ranging from gas separation and storage,
catalysis, and sensing. The attractive feature of MOFs is that, by
changing the ligand and/or metal, they can be chemically tuned to
perform optimally for a given application. In most, if not all, of
these applications one also needs a material that has a sufficient
mechanical stability, but our understanding of how changes in the
chemical structure influence mechanical stability is limited. In this
work, we rationalize how the mechanical properties of MOFs are related
to framework bonding topology and ligand structure. We illustrate
that the functional groups on the organic ligands can either enhance
the mechanical stability through formation of a secondary network
of nonbonded interactions or soften the material by destabilizing
the bonded network of a MOF. In addition, we show that synergistic
effect of the bonding network of the material and the secondary network
is required to achieve optimal mechanical stability of a MOF. The
developed molecular insights in this work can be used for systematic
improvement of the mechanical stability of the materials by careful
selection of the functional groups.