Melt-quenched carboxylate metal-organic framework glasses.

Kim, Minhyuk; Lee, Hwa-Sub; Seo, Dong-Hyun; Cho, Sung June; Jeon, Eun-Chae; Moon, Hoi Ri · Nat Commun · 2024

basic_science · Level V

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Abstract

Although carboxylate-based frameworks are commonly used architectures in metal-organic frameworks (MOFs), liquid/glass MOFs have thus far mainly been obtained from azole- or weakly coordinating ligand-based frameworks. This is because strong coordination bonds of carboxylate ligands to metals block the thermal vitrification pathways of carboxylate-based MOFs. In this study, we present the example of carboxylate-based melt-quenched MOF glasses comprising Mg<sup>2+</sup> or Mn<sup>2+</sup> with an aliphatic carboxylate ligand, adipate. These MOFs have a low melting temperature (T<sub>m</sub>) of 284 °C and 238 °C, respectively, compared to zeolitic-imidazolate framework (ZIF) glasses, and superior mechanical properties in terms of hardness and elastic modulus. The low T<sub>m</sub> may be attributed to the flexibility and low symmetry of the aliphatic carboxylate ligand, which raises the entropy of fusion (ΔS<sub>fus</sub>), and the lack of crystal field stabilization energy on metal ions, reducing enthalpy of fusion (ΔH<sub>fus</sub>). This research will serve as a cornerstone for the integration of numerous carboxylate-based MOFs into MOF glasses.