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Ultrahigh-field 67Zn NMR reveals short-range disorder in zeolitic imidazolate framework glasses

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Science  27 Mar 2020:
Vol. 367, Issue 6485, pp. 1473-1476
DOI: 10.1126/science.aaz0251

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Glassy metal-organic frameworks

The node-and-linker structure of metal-organic frameworks could enable detailed structural studies of molecular glasses quenched from melts. Zinc-based zeolitic imidazole frameworks exhibit a high propensity for glass formation at conventional cooling rates. Madsen et al. used ultrahigh magnetic fields (19.5 and 35.2 tesla) to perform zinc-67 nuclear magnetic resonance of solid samples with magic-angle spinning on three samples with different ratios of imidazole and benzimidazole linkers. The structural disorder of the tetrahedral ligand environment around zinc nodes was higher in the glassy states than in the parent crystals.

Science, this issue p. 1473

Abstract

The structure of melt-quenched zeolitic imidazole framework (ZIF) glasses can provide insights into their glass-formation mechanism. We directly detected short-range disorder in ZIF glasses using ultrahigh-field zinc-67 solid-state nuclear magnetic resonance spectroscopy. Two distinct Zn sites characteristic of the parent crystals transformed upon melting into a single tetrahedral site with a broad distribution of structural parameters. Moreover, the ligand chemistry in ZIFs appeared to have no controlling effect on the short-range disorder, although the former affected their phase-transition behavior. These findings reveal structure-property relations and could help design metal-organic framework glasses.

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