Engineering Structural Dynamics of Zirconium Metal-Organic Frameworks Based on Natural C4 Linkers.

Engineering the structural flexibility of metal-organic framework (MOF) materials for separation-related applications remains a great challenge. We present here a strategy of mixing rigid and soft linkers in a MOF structure to achieve tunable structural flexibility, as exemplified in a series of stable isostructural Zr-MOFs built with natural C4 linkers (fumaric acid, succinic acid, and malic acid). As shown by the differences in linker bond stretching and bending freedom, these MOFs display distinct responsive dynamics to external stimuli, namely, changes in temperature or guest molecule type. Comprehensive in situ characterizations reveal a clear correlation between linker character and MOF dynamic behavior, which leads to the discovery of a multivariate flexible MOF. It shows an optimal combination of both good working capacity and significantly enhanced selectivity for CO2/N2 separation. In principle, it provides a new avenue for potentially improving the ability of microporous MOFs to separate other gaseous and liquid mixtures.