Flexibility and Sorption Selectivity in Rigid Metal-Organic Frameworks: The Impact of Ether-Functionalised Linkers

The functionalisation of well‐known rigid metal–organic frameworks (namely, [Zn4O(bdc)3]n, MOF‐5, IRMOF‐1 and [Zn2(bdc)2(dabco)]n; bdc=1,4‐benzene dicarboxylate, dabco=diazabicyclo[2.2.2]octane) with additional alkyl ether groups of the type ‐O‐(CH2)n‐O‐CH3 (n = 2–4) initiates unexpected structural flexibility, as well as high sorption selectivity towards CO2 over N2 and CH4 in the porous materials. These novel materials respond to the presence/absence of guest molecules with structural transformations. We found that the chain length of the alkyl ether groups and the substitution pattern of the bdc‐type linker have a major impact on structural flexibility and sorption selectivity. Remarkably, our results show that a high crystalline order of the activated material is not a prerequisite to achieve significant porosity and high sorption selectivity. Just breathe! The implementation of linkers functionalised with flexible ether groups in known, but rigid metal–organic frameworks (MOFs), yields isoreticular frameworks that exhibit unexpected responsiveness towards small molecules and high sorption selectivity for CO2 (see figure).