Structural transitions of the metal-oxide nodes within metal-organic frameworks: On the local structures of NU-1000 and UiO-66

Platero-Prats, A. E.; Mavrandonakis, A.; Gallington, L. C.; Liu, Y.; Hupp, J. T.; Farha, O.; Cramer, C. J.; Chapman, K. W.
J. Am. Chem Soc. 2016, 138, 4178 (doi:10.1021/jacs.6b00069).

In situ pair distribution function (PDF) analyses and density functional theory (DFT) computations are used to probe local structural transitions of M₆O₈ nodes found in two metal organic frameworks (MOFs), NU-1000 and UiO-66, for M=Zr, Hf. Such transitions are found to occur without change to the global framework symmetry at temperatures within a range relevant to many potential MOF applications. For the particular M₆(O)₈ nodes studied here, the observed distortions can be mapped to polymorphic forms known for bulk ZrO₂. In the MOF framework, however, node distortions are found to occur at substantially lower temperature than analogous distortions in bulk ZrO₂ owing to the nanoscale nature of the former.