Local order, disorder, and everything in between: using 91Zr solid-state NMR spectroscopy to probe zirconium-based metal–organic frameworks†

Characterization of metal centers in metal–organic frameworks (MOFs) is critical for rational design and further understanding of structure–property relationships. The short-range structure about Zr atoms is challenging to properly elucidate in many Zr MOFs, particularly when local disorder is present. Static ⁹¹Zr solid-state NMR spectra of the seven zirconium MOFs UiO-66, UiO-66-NH₂, UiO-67, MOF-801, MOF-808, DUT-68 and DUT-69 have been acquired at high magnetic fields of 35.2 T and 19.6 T, yielding valuable information on the local structure, site symmetry and order about Zr. ⁹¹Zr NMR is very sensitive to differences in MOF short-range structure caused by guest molecules, linker substitution and post-synthetic treatment. Complementary density functional theory (DFT) calculations assist in the interpretation and assignment of ⁹¹Zr solid-state NMR spectra, lend insight into structural origins of ⁹¹Zr NMR parameters and enable determination of local Zr coordination environments. This approach can be extended to many other materials containing zirconium.