Beyond the control of metal centers and organic linker functionalization, there are other avenues open to researchers wishing to control or design flexibility in framework materials. Several research groups have demonstrated the impact of the presence of defects, such as missing linkers, on the flexibility of MOFs. Ohsaki et al. showed, for example, how the introduction of defects could tune the gate opening behavior of a MOF. They introduced a controled amount of defects in the interdigitated CID-4 framework through the use of modulators (monodentate ligands replacing bidentate organic linkers), and observed that the gate opening pressure for nitrogen sorption could be varied. Free energy analysis of the adsorption isotherms showed that the change in gating pressure was directly linked to a destabilization of the closed structure, i.e., a change in the ∆F host free energy difference between the two phases of the material, due to intermolecular host-host interactions.