Recent research on
metal–organic frameworks (MOFs) has shown
a shift from considering only the crystalline high-porosity phases
to exploring their amorphous counterparts. Applying pressure to a
crystalline MOF is a common method of amorphization, as MOFs contain
large void spaces that can collapse, reducing the accessible surface
area. This can be either a desired change or indeed an unwanted side
effect of the application of pressure. In either case, understanding
the MOF’s pressure response is extremely important. Three such
MOFs with varying pore sizes (UiO-66, MOF-808, and NU-1000) were investigated
usingin situhigh-pressure X-ray diffraction and
Raman spectroscopy. Partial crystallinity was observed in all three
MOFs above 10 GPa, along with some recovery of crystallinity on return
to ambient conditions if the frameworks were not compressed above
thresholds 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 increase
in one or more lattice parameters with pressure in all MOFs. Comparison
of compressibility between MOFs suggests penetration of the pressure-transmitting
oil into MOF-808 and NU-1000. The survival of some crystallinity above
10 GPa in all of these MOFs despite their differing pore sizes and
extents of oil penetration demonstrates the importance of high-pressure
characterization of known structures.