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 local structure of 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 local 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.