We have discovered and clarified the ultrahigh glass-forming ability of the metal-organic frameworks—ZIF-62 [Zn(Im2−xbImx)].

The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create a class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of MOF crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix. The coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the interfacial interactions between the closely contacted microdomains improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling in the presence of water, is stabilised at room temperature in the crystal-glass composite. This leads to a significant improvement of CO 2 adsorption capacity.

Stable emission in glass Lead halide perovskites can exhibit bright, narrow band photoluminescence but have stability issues related to formation of inactive phases and the loss of lead ions. Hou et al . show that the black, photoactive phase of cesium lead iodide can be stabilized by forming a composite with a glassy phase of a metal-organic framework through liquid-phase sintering. The photoluminescence is at least two orders of magnitude greater than that of the pure perovskite. The glass stabilizes the perovskite under high laser excitation, and about 80% of the photoluminescence was maintained after 10,000 hours of water immersion. —PDS

The synthesis of four novel crystalline zeolitic imidazolate framework (ZIF) structures using a mixed-ligand approach is reported. The inclusion of both imidazolate and halogenated benzimidazolate-derived linkers leads to glass-forming behavior by all four structures. Melting temperatures are observed to depend on both electronic and steric effects. Solid-state NMR and terahertz (THz)/Far-IR demonstrate the presence of a Zn-F bond for fluorinated ZIF glasses. In situ THz/Far-IR spectroscopic techniques reveal the dynamic structural properties of crystal, glass and liquid phases of the halogenated ZIFs, linking the melting behavior of ZIFs to the propensity of the ZnN4 tetrahedra to undergo thermally-induced deformation. The inclusion of halogenated ligands within MOFglasses improves their gas uptake properties.

To date, only several microporous, and even fewer nanoporous, glasses have been produced, always via post synthesis acid treatment of phase separated dense materials, e.g. Vycor glass. In comparison, high internal surface areas are readily achieved in crystalline materials, such as metal-organic frameworks (MOFs). It has recently been discovered that a new family of melt quenched glasses can be produced from MOFs, though they have thus far have lacked the accessible and intrinsic porosity of their crystalline precursors. Here, we report the first glasses that are permanently, and reversibly porous toward incoming gases, without post synthetic treatment. We characterized the structure of these glasses using a range of experimental techniques, and demonstrate pores in the 4-8 angstrom range. The discovery of MOF-glasses with permanent accessible porosity reveals a new category of porous glass materials, that are potentially elevated beyond conventional inorganic and organic porous glasses, by their diversity and tunability.