Melt-quenched carboxylate metal-organic framework glasses

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 Mg2+ or Mn2+ with an aliphatic carboxylate ligand, adipate. These MOFs have a low melting temperature (Tm) of 284 degrees C and 238 degrees C, respectively, compared to zeolitic-imidazolate framework (ZIF) glasses, and superior mechanical properties in terms of hardness and elastic modulus. The low Tm may be attributed to the flexibility and low symmetry of the aliphatic carboxylate ligand, which raises the entropy of fusion (Delta Sfus), and the lack of crystal field stabilization energy on metal ions, reducing enthalpy of fusion (Delta Hfus). This research will serve as a cornerstone for the integration of numerous carboxylate-based MOFs into MOF glasses. Many MOFs feature carboxylate ligands with strong coordination bonds, hindering thermal melting. Here, authors present a meltable carboxylate MOF designed with a thermodynamically favored component.