The reaction of Zn-MOF-74 is particularly interesting for its distinct colour changes and documented intermediate phase. Use of clear PMMA milling jars permitted observation of these changes during milling (figure ). The starting mixture appears bright yellow due to the presence of 2,5-dihydroxyterephthalic acid, but it quickly transforms to a pale yellow, and eventually a white colour. The observation of white material is evidence of the intermediate, Zn The zinc oxide contains minimal hydrogen which is apparent in figure . Any observed signal can be ascribed to background signal from the probe, and possible impurities in the zinc oxide sample. The 2,5-dihydroxyterephthalic acid correlation plot (figure ) shows a single short lifetime T2* of 12 µs. The T1 value at the center of the peak is at 48 s and at the very left side of the peak it is 0.11 s. The FID shows a clear sinc-gaussian decay (SM, see section S3).