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 [Zn-2(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 N-2 and CH, 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.