Hybrid glasses from melt-quenched metal-organic frameworks (MOFs) have been emerging as a new class of materials, which combine the functional properties of crystalline MOFs with the processability of glasses. However, only a handful of the crystalline MOFs are meltable. Porosity and metal-linker interaction strength have both been identified as crucial parameters in the trade-off between thermal decomposition of the organic linker and, more desirably, melting. For example, the inability of the prototypical zeolitic imidazolate framework (ZIF) ZIF-8 to melt, is ascribed to the instability of the organic linker upon dissociation from the metal center. Here, we demonstrate that the incorporation of an ionic liquid (IL) into the porous interior of ZIF-8 provides a means to reduce its melting temperature to below its thermal decomposition temperature. Our structural studies show that the prevention of decomposition, and successful melting, is due to the IL interactions stabilizing the rapidly dissociating ZIF-8 linkers upon heating. This understanding may act as a general guide for extending the range of meltable MOF materials and, hence, the chemical and structural variety of MOF-derived glasses.

ABSTRACT:The coefficient of thermal expansion of ZrMgMo 3 O 12 has been measured and was found to be extremely close to zero over a wide temperature range including room temperature (α = (1.6 ± 0.2) × 10 −7 K −1 from 25 to 450°C by X-ray diffraction (XRD)). ZrMgMo 3 O 12 belongs to the family of AMgM 3 O 12 materials, for which coefficients of thermal expansion have previously been reported to range from low-positive to low-negative. However, the low thermal expansion property had not previously been explained because atomic position information was not available for any members of this family of materials. We determined the structure of ZrMgMo 3 O 12 by nuclear magnetic resonance (NMR) crystallography, using 91 Zr, 25 Mg, 95 Mo, and 17 O magic angle spinning (MAS) and 17 O multiple quantum MAS (MQMAS) NMR in conjunction with XRD and density functional theory calculations. The resulting structure was of sufficient detail that the observed zero thermal expansion could be explained using quantitative measures of the properties of the coordination polyhedra. We also found that ZrMgMo 3 O 12 shows significant ionic conductivity, a property that is also related to its structure.

Metal-organic framework (MOF) glasses have become a subject of interest as a distinct category of melt quenched glass, and have potential applications in areas such as ion transport and sensing. In this paper we show how MOF glasses can be combined with inorganic glasses in order to fabricate a new family of materials composed of both MOF and inorganic glass domains. We use an array of experimental techniques to propose the bonding between inorganic and MOF domains, and show that the composites produced are more mechanically pliant than the inorganic glass itself.

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Given the ubiquity of glass formulations that are functionalized with silver compounds, the electronic interaction between isolated silver cations and the glass network deserves more attention. Here, we report the structural origin of the optical properties that result from silver doping in fluorophosphate (PF) and sulfophosphate (PS) glasses. To achieve this, solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) are combined with optical spectroscopic analysis and physical property measurements. Comparing the 31 P NMR, 27 Al 1d NMR, and 27 Al multi-quantum magic-angle spinning NMR of doped glasses and glasses with large amounts of Ag + added, we deduce silver's bonding preference in these mixed-anion aluminophosphate glasses. We show that such understanding provides an explanation for the large Stokes shift observed for Ag + in PF and PS glasses, which is related to absorption by the ionic Ag + ••• − O−P species and transfer of the excitation energy within more covalently bonded Ag 2 O-like clusters. This is corroborated by DFT calculations, which show that the Ag + ••• − O−P and Ag + ••• − O−S bonds in corresponding crystals are mostly ionic. The introduction of more silver ions into the crystal structure results in more covalent bonding between Ag + and the phosphate matrix.