Defect engineering of metal–organic frameworks (MOFs) offers promising opportunities for tailoring their properties to specific functions and applications. However, determining the structures of defects in MOFs—either point defects or extended ones—has proved challenging owing to the difficulty of directly probing local structures in these typically fragile crystals. Here we report the real-space observation, with sub-unit-cell resolution, of structural defects in the catalytic MOF UiO-66 using a combination of low-dose transmission electron microscopy and electron crystallography. Ordered ‘missing linker’ and ‘missing cluster’ defects were found to coexist. The missing-linker defects, reconstructed three-dimensionally with high precision, were attributed to terminating formate groups. The crystallization of the MOF was found to undergo an Ostwald ripening process, during which the defects also evolve: on prolonged crystallization, only the missing-linker defects remained. These observations were rationalized through density functional theory calculations. Finally, the missing-cluster defects were shown to be more catalytically active than their missing-linker counterparts for the isomerization of glucose to fructose.
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The authors declare that all the data supporting the findings of this study are available within the paper and the Supplementary Information, and/or from the authors upon reasonable request.
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This research was supported by Competitive Center Funds (FCC/1/1972-19) to Y.H. and M.E. from King Abdullah University of Science and Technology. This research used resources of the Core Labs of King Abdullah University of Science and Technology. Yi.Z. acknowledges financial support from the National Natural Science Foundation of China (21771161) and the Thousand Talents Program for Distinguished Young Scholars. S.L. and B.S. are thankful to the Materials Chemistry Consortium (EPSRC: EP/L000202) for provision of computer time on ARCHER UK National Supercomputing Service. B.S. acknowledges the Royal Society for financial support through an industry fellowship (F160062). The authors acknowledge helpful discussions with A. Goodwin, M. Cliffe and G. Shearer.
The authors declare no competing interests.
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Methods; Supplementary Figs. 1–16; Supplementary Tables 1–5; Supplementary refs. 1–14
Atomic coordinates of optimised fcu structure
Atomic coordinates of optimised bcu structure
Atomic coordinates of optimised reo structure
Atomic coordinates of optimised scu structure
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Liu, L., Chen, Z., Wang, J. et al. Imaging defects and their evolution in a metal–organic framework at sub-unit-cell resolution. Nat. Chem. 11, 622–628 (2019). https://doi.org/10.1038/s41557-019-0263-4
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