Defects within a material can make a big difference to how it behaves. Metal-organic frameworks (MOFs) are no exception and nanodomains of correlated missing metal centers within crystals of the MOF UiO-66 have been shown to both affect properties and to be controllable through synthesis. However, these defect nanodomains have not previously been imaged directly because they occur on a length scale (10-150 nm) between bulk characterization techniques and atomic resolution imaging, which is challenging to assess. Electron microscopy can be used to address this length scale but the electron beam typically destroys sensitive materials, like MOFs, very rapidly. In this paper, we collaborated with teams based at the Universities of Nottingham and Leeds and the Department of Chemistry in Cambridge to directly image entire defect nanodomains in a MOF for the first time using low-dose scanning electron diffraction.

Figure: The defect phase of UiO-66 (reo, green) with missing metal centres as compared with the ideal UiO-66 structure (fcu, magenta) distinguished based on Bragg diffraction peaks present only in the defect phase that are used to image the defect nanodomains directly.