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

Abstract

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 using in situ high-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.

Spin-state dependent pressure responsiveness of Fe(ii)-based triazolate metal–organic frameworks

“…3), see ESI† for the measurement of a standard material (S-32). Silicone oil AP-100 was used as a pressure transmitting medium (PTM), which has previously been applied for HPPXRD experiments of Zr-based MOFs 47 and molecular perovskites. 48 To the best of our knowledge, silicone oil AP-100 acts as hydrostatic, non-penetrating PTM, enabling to study the mechanical response of the MOFs without any additional effects such as penetration of the PTM into the pores of the MOF.…”

Fluorescence Turn-on Detection of Perfluorooctanoic Acid (PFOA) by Perylene Diimide-Based Metal–Organic Framework

“…The shift in Bragg diffraction peak positions toward lower 2θ values after PFOA sensing was confirmed by PXRD analysis (Figure S40). This low-angle shift suggests an increase in cell volume after PFOA interaction . To confirm this change, a Pawley refinement was attempted postsensing.…”

Exploring the Role of Ligand Connectivity in MOFs Mechanical Stability: The Case of MIL-100(Cr)

“…However, Redfern et al also showed that the linker length and the nearest node distance play an important role in the framework response to compression, highlighting how even minor differences in the structure can strongly affect the bulk modulus . One of the key parameters in MOFs structure that defines their topology is the linker connectivity, also known as topicity, which identifies how many metal nodes a single linker molecule can connect to within the MOF network. , Identifying MOFs with the same topology and different linker topicity and comparing their behavior at high pressure could help in assessing the role played by this parameter in the framework mechanical stability …”

“…This is due to different experimental methods or the lack of experimental details. As an example, reported values of the UiO-66­(Zr) bulk modulus span between 15 and 37.9 GPa. − Such different values are probably the result of different defect concentrations present in the framework, burdensome quantity to determine experimentally. ,, Moreover, it is well known that guest molecules can penetrate into the pores and significantly impact the high-pressure behavior of MOFs and thus the bulk moduli reported in the literature. ,− A recent study by Redfern and co-workers explores the relationship between the structural parameters of two isoreticular MOF series, the UiO and the NU-900 series. They observe that for both topologies, the bulk modulus is inversely correlated with void fraction, which is in agreement with a computational study showing that the bulk modulus is inversely proportional to the pore diameter for 3000 frameworks .…”