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X-ray Electron Density Study of the Chemical Bonding Origin of Glass Formation in Metal–Organic Frameworks

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Glass-forming metal–organic frameworks (MOFs) have novel applications, but the origin of their peculiar melting behavior is unclear. Here, we report synchrotron X-ray diffraction electron densities of two zeolitic imidazolate frameworks (ZIFs), the glass-forming Zn-ZIF-zni and the isostructural thermally decomposing Co-ZIF-zni. Electron density analysis shows that the Zn−N bonds are more ionic than the Co−N bonds, which have distinct covalent features. Variable-temperature Raman spectra reveal the onset of significant imidazolate bond weakening in Co-ZIF-zni above 673 K. Melting can be controlled by tuning the metal–ligand and imidazole bonding strength as shown from thermal analysis of nine solid-solution CoxZn1−x-ZIF-zni (x=0.3 to 0.003) MOFs, and a mere 4 % Co-doping into Zn-ZIF-zni results in thermal decomposition instead of melting. The present findings demonstrate the key role of the metal–ligand bonds and imidazolate bonds in controlling the delicate balance between melting and decomposition processes in this class of ZIF compounds.

Original languageEnglish
Article number202202742
JournalAngewandte Chemie - International Edition
Number of pages8
Publication statusPublished - May 2022

Bibliographical note

Publisher Copyright:
© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

    Research areas

  • Chemical Bonding, Doping, Electron Density, Melting, Metal–Organic Frameworks, CHARGE-DENSITY, Metal-Organic Frameworks, AMORPHIZATION, LIQUID, CHEMISTRY

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