Beyond the possibility of a single substitution, some research groups have studied the effect of a series of linker substituents. Sugamata et al. demonstrated the possibility to control the flexibility of carbazole-based MOFs through the introduction of electron-donating groups. They showed that these groups, attached onto the central benzene ring of the carbazole ligand, reduced the flexibility of the parent copper-based MOF in the order of the Hammett σ m coefficient of the substituent. In a different example of the same idea, Roztocki et al. attained a precise control of the gate-opening flexibility of materials of the JUK-8 family (JUK = Jagiellonian University in Kraków), for the purpose of CO 2 adsorption, by incorporating halogen substituents of increasing size (JUK-8X, with X = F, Cl, Br, or I). In this acylhydrazone-based family of eight-fold interpenetrated MOFs, the nature of the halogen functional group influences both the maximum adsorption capacity, the strength of host-guest interactions, and in turn the pressure at which gate opening occurs for CO 2 (see Figure ) -as confirmed through density functional theory (DFT) calculations and in situ powder X-ray diffraction (PXRD) measurements.