Cationic Covalent Organic Framework‐Based Membranes for High‐Performance Zn/Br2 Redox Flow Batteries

Inclusion of cationic covalent organic frameworks into Nafion membranes regulates the bi-ion flow between the compartments of Zn/Br2 redox flow batteries, leading to supression of polybromide shuttle...

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Xenon adsorption-induced flexibility of the zeolitic imidazolate framework ZIF-4 observed by in situ 129Xe NMR spectroscopy

In situ 129Xe NMR spectroscopy reveals an unexpected, xenon adsorption-induced flexibility of ZIF-4. Beyond a certain threshold pressure, xenon induces a structural transition at low temperature. This...

pubs.rsc.org

Orientational Disorder of NH3 in Hexammine Magnesium Borohydride

Hexammine magnesium borohydride, Mg(NH3)6(BH4)2, consists of adducted NH3 molecules locked in a matrix of Mg cations and borohydride anions. It is a candidate material for hydrogen storage, with 16.8 wt % hydrogen stored in both the NH3 and borohydride anions. It may also be of interest as an Mg2+-conducting electrolyte in solid-state batteries. Its crystal structure has, until now, eluded a proper structural solution due to ambiguity regarding the NH3 position and behavior. In this work, we show using synchrotron X-ray diffraction that the room-temperature structure can be solved only with a model assuming the orientational disorder of ammonia molecules within the crystal structure. Cooling the sample to 120 K yields additional Bragg peaks, which can be solved only with a unit cell expansion consistent with the freezing of the orientational freedom of ammonia molecules. Using this insight from the structure solution, we performed a full assignment of the vibrational modes in the room-temperature infrared spectrum.

pubs.acs.org

Mechanochemical Synthesis Enables Melting, Glass Formation and Glass–Ceramic Conversion in a Cadmium-Based Zeolitic Imidazolate Framework

Metal-organic frameworks (MOFs) are versatile materials with tunable properties and broad applications. Here, we report the first cadmium-based zeolitic imidazolate framework (ZIF) glass, prepared by melt-quenching sub-micrometer-sized Cd(im)2 particles (im– = imidazolate) obtained via mechanochemical synthesis. This route increases defect density and reduces crystallite domain size, lowering the melting temperature from 461 °C (for larger solution-synthesized microcrystals) to 455 °C, thereby mitigating thermal decomposition during melting. Crystalline Cd(im)2 adopts a two-fold interpenetrated diamondoid (dia-c) topology, assembled from tetrahedral Cd2+ centers and im– linkers. Rapid cooling of the Cd(im)2 melt yields a monolithic glass with a glass transition temperature (Tg) of 175 °C. Structural analysis confirms that short-range connectivity within individual networks is maintained, whereas interactions between the interpenetrated networks are disrupted in the glass. Upon reheating, partial recrystallization produces a single-component glass–ceramic with enhanced mechanical properties, an unprecedented behavior in melt-quenched ZIF glasses. Investigations of thermal parameters (cooling rates) and partial linker substitution reveal strategies for tuning the phase behavior of both glass and glass–ceramic. These findings extend ZIF glass systems to second-row transition metal ions and underscore mechanochemical synthesis as a tool for tailoring the thermal properties of MOFs. This dual-phase functionality, combining glassy and crystalline domains of identical composition within a single material, offers potential for applications in thermal energy storage, phase change memory, and optics.

doi.org

Ideal Molecular Sieving with a Dense MOF for Helium Upgrading with Highly Diffusion Selective Mixed Matrix Membranes

The separation of Helium gas from natural gas is challenging but highly important. MIL-116(Ga), a “non-porous” metal–organic framework is used as a molecular sieve to separate He from CH4. Druse-like...

advanced.onlinelibrary.wiley.com

Defect Identification in Zeolitic Imidazolate Framework Glasses by Solid-State NMR Spectroscopy Using 13CO2 as Probe

Melt-quenched glasses from zeolitic imidazolate frameworks (ZIFs), a subset of metal–organic frameworks (MOFs) constructed from imidazolate linkers and divalent metal ions, represent a novel class of ...

pubs.acs.org

Electron-deficient two-dimensional poly(arylene vinylene) covalent organic frameworks: efficient synthesis and host–guest interaction

Crystalline and porous 2D poly(arylene vinylene)s (2D PAVs), i.e. vinylene-linked 2D conjugated covalent organic frameworks, represent promising materials for electronic and electrochemical applicatio...

pubs.rsc.org

Ideal Molecular Sieving with a Dense MOF for Helium Upgrading with Highly Diffusion Selective Mixed Matrix Membranes

Helium is one of the most critical resources of our planet, as it is a finite resource, cannot be produced from radioactive decay in sufficient amounts and escapes our atmosphere, while being extraord...

chemrxiv.org