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.1,2 This is because strong coordination bonds of carboxylate ligands to metals block the thermal vitrification pathways of carboxylate-based MOFs.3 In this study, we present the first example of carboxylate-based melt-quenched MOF glasses comprising Mg2+ or Mn2+ and an aliphatic carboxylate ligand, adipate. These MOF have a low melting temperature (Tm) of 284 °C, compared to zeolitic-imidazolate framework (ZIF) glasses,4,5 and superior mechanical properties in terms of hardness and elastic modulus.6 The low Tm is due to the flexibility and low symmetry of the aliphatic carboxylate ligand (raising entropy of fusion (ΔSfus))7,8 and the lack of crystal field stabilization energy on metal ions (reducing enthalpy of fusion (ΔHfus)).9 This research will serve as a cornerstone for the integration of numerous carboxylate-based MOF into MOF glasses.

Functional metal–organic liquids

“…2 and 3). 44,45,48,53,77,78 Before getting into the details, it is crucial to establish a clear understanding of the term "metal-organic liquid" and describe the scope of this review. Broadly, this term encompasses liquid materials comprising metal ions and organic components that link into repeating entities under certain states.…”

“…46,47 Mg 4 (adipate) 4 (DMA)(H 2 O). 48 Imidazolate: Cu(isopropylimidazolate). 30,49 Linker exchanged ZIF-8 (Zn(mIm) 2x (Im) 2y (mbIm) 2z , (x + y + z = 1), mIm = methylimidazolate, Im = imidazolate, bIm = benzimidazolate).…”

“…(TPrA)[M(dca) 3 ] (TPrA = tetrapropylammonium, dca = dicyanamide) 46,47. Mg 4 (adipate) 4 (DMA)(H 2 O) 48. Imidazolate: Cu(isopropylimidazolate) 30,49.…”