Guest Molecules Play Tug of War in a Breathing MOF: The Stepwise Monitoring of an Elastic Framework Deformation via SC-SC Transformations

Metal-organic frameworks (MOFs) keep attracting the attention of many research groups worldwide who are aiming at using them as crystalline sponges, thus loading their porous structures with any kind of molecules of interest. Among other desiderata, framework flexibility is the golden property that an MOF must have to adapt its structure throughout the loading and release process of guest molecules. Here, we highlight the flexibility of a breathing MOF by soaking the crystals of the mixed-ligand MOF PUM168 into different solvents, ranging from acetonitrile (ACN) to THF and diethyl ether, revealing a systematic framework twisting observed via single-crystal-to-single-crystal transformations during the DMF-solvent exchange. Reversible chemical pathways have successfully been reported and confirmed via FT-IR and H-1 NMR. Soaking in ACN resulted in the most effective strategy in terms of the solvent-exchange activation of the pristine MOF, leading to a complete extrusion of the native solvent from the structure while keeping the porous channels widely open.