In the second shell, the peak from the edge-sharing Zr-Zr pairs at 3.53 Å disappears, and two new peaks appear: one with a shorter distance of 3.41 Å and one with a longer distance of 3.94 Å. Similar structural changes have been observed in other Zr-MOFs, such as UiO-66 and NU-1000, by Platero-Prats et al. where elevated temperatures cause a shift from cubic to monoclinic-like structures due to node distortions. Although neither cubic, tetragonal, nor monoclinic ZrO 2 fits the local structure of aDUT-67 well (Figure ), m-ZrO 2 indeed reproduces the first three peaks relatively well. However, longer treatments form a mixed phase of cubic/tetragonal c/t-ZrO 2 as shown by the fits to the 6-hour sample in Figure . Notably, the low peak heights of the second-shell Zr-Zr pairs, relative to the first-shell Zr-O peak, in aDUT-67 suggest that the structure still consists of discrete clusters (Figure and Figure ).