Cooperative Sieving and Functionalization of Zr Metal-Organic Frameworks through Insertion and Post-Modification of Auxiliary Linkers.

A major goal of metal-organic framework (MOF) research is to control the structures and functions of materials in accordance with their specific applications. However, due to the flexible coordination modes between metal ions and organic linkers in MOFs, it is still challenging to rationally assemble a framework with deliberate structures and desired functional groups. Sometimes, two or more phases coexist in a one-pot reaction, making them difficult to separate. To this end, sieving and purification of MOF mixtures become vital for the following application. Herein, we demonstrate that the formation of zirconium-based MOFs (Zr-MOFs) can be regulated in a wider two-dimensional scale by thermodynamics using auxiliary linkers. The auxiliary linkers favor the formation of the targeted Zr-MOF by selectively binding to its coordination vacancies and therefore increasing its formation enthalpy to achieve the sieving of MOF mixture. Furthermore, the resulting mixed-linkers MOFs not only maintain porosities but also contain the installed auxiliary linkers as chemical handles to further incorporate functional groups, providing the possibility of introduction of active sites through post-modification. Finally, this synthetic strategy was applied to assemble a cooperative catalytic system in a MOF platform for CO2 cycloaddition with epoxides. To the best of our knowledge, this is the first example of sieving and functionalization of MOFs through insertion and post-modification of auxiliary linkers.