Survival of Zirconium-Based Metal-Organic Framework Crystallinity at Extreme Pressures

Recent research onmetal-organic frameworks (MOFs) has showna shift from considering only the crystalline high-porosity phasesto exploring their amorphous counterparts. Applying pressure to acrystalline MOF is a common method of amorphization, as MOFs containlarge void spaces that can collapse, reducing the accessible surfacearea. This can be either a desired change or indeed an unwanted sideeffect of the application of pressure. In either case, understandingthe MOF's pressure response is extremely important. Three suchMOFs with varying pore sizes (UiO-66, MOF-808, and NU-1000) were investigatedusing in situ high-pressure X-ray diffraction andRaman spectroscopy. Partial crystallinity was observed in all threeMOFs above 10 GPa, along with some recovery of crystallinity on returnto ambient conditions if the frameworks were not compressed abovethresholds of 13.3, 14.2, and 12.3 GPa for UiO-66, MOF-808, and NU-1000,respectively. This threshold was marked by an unexpected increasein one or more lattice parameters with pressure in all MOFs. Comparisonof compressibility between MOFs suggests penetration of the pressure-transmittingoil into MOF-808 and NU-1000. The survival of some crystallinity above10 GPa in all of these MOFs despite their differing pore sizes andextents of oil penetration demonstrates the importance of high-pressurecharacterization of known structures. Zirconium-basedmetal-organic frameworks UiO-66,MOF-808, and NU-1000 were investigated in situ underextreme pressures using X-ray diffraction. They all showed survivingcrystallinity at pressures of >10 GPa. Their opposing trends ofcompressibilityand porosity are ascribed to varying interactions with the siliconeoil pressure-transmitting medium.