Andreas Schneemann

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 porous materials with potential applications in gas separation, optics, and as battery materials. Volumetric adsorption studies in combination with high-pressure 13C in situ NMR spectroscopy of CO2 have emerged as promising tools to investigate the textural properties of porous materials, including ZIFs. However, CO2 is not inert. It can chemically bind to Lewis basic sites present in the pores, thus changing the identity of CO2. Here, we use this property to investigate dangling linker defects in crystalline ZIFs and their corresponding glasses or mechanochemically amorphized derivatives before and after exposure to 13C-enriched CO2 at high pressure via solid-state NMR spectroscopy. Dangling linkers in the porous materials are visualized spectroscopically via carboxylation at their non-coordinating N atoms, forming carbamates. We observe that the carboxylation reaction of dangling linkers is much more pronounced in ZIF glasses than in the crystalline parent compounds, substantiating that the glasses feature a considerably higher concentration of such defects. Quantitative 13C NMR spectroscopy reveals that approximately 1% of the imidazolate-type linkers are carboxylated in glasses, whereas the amount of the carboxylated linkers is about seven times lower in the pristine ZIFs. These findings offer structural insight into the defects of ZIF glasses and bear significant practical implications for applications ranging from gas separation to catalysis.

Tobias uncovered this behavior at the same time when we also discovered the reactivity of ZIF glasses towards CO2, previously published in Chemistry of Materials @acs.org pubs.acs.org/doi/full/10....

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...

Now in @chemcomm.rsc.org - the Xenon induced phase transition in ZIF-4 uncovered by solid state NMR during 129Xe adsorption. Congratulations to Tobias from the Brunner group @tudresden.bsky.social and @henkegroup.bsky.social, @wenlong-xue.bsky.social !

pubs.rsc.org/en/content/a...

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.

Now in Inorganic Chemistry @acs.org 📄! Collaboration with Nick and Liam from SSRL ⚠️ Treating of Mg(BH4)2 with liquid ammonia yields the hexammine (NH3)6Mg(BH4)2 whose structure was solved🔎 using radiation from SLAC. Congrats to the team NREL, @sandialabs.bsky.social ! pubs.acs.org/doi/10.1021/...

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.

New paper just out @jacs.acspublications.org In his 3rd first-author paper from his PhD, Wen-Long Xue shows that mechanochemical synthesis enables melting & glass formation of a Cd-based MOF, plus controlled nanocrystal growth to form MOF glass-ceramics. A great team effort!
doi.org/10.1021/jacs...

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...

Congratulations to Ayisha from the Team of @knebelalexander.bsky.social
On her paper out in Advanced Functional Materials! Nominally "non-porous" MIL-116(Ga) can be used for Helium Upgrading! Glad we could help! advanced.onlinelibrary.wiley.com/doi/10.1002/...

We have thought about it - the problem is that we need the dangling linker defects for the reaction to happen and their concentration is for practical carbon capture quite low.
Maybe if you can design a material with imidazolates lining the walls, this could be quite interesting!

Missing linker defects form carbonates. After combined 13CO2 adsorption + NMR experiments, new signals appeared in the 13C-MAS NMR 😮. Now, we have a cool new tool to identify and quantify defects in ZIFs and their melt quenched glasses!

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 ...

Beware of the defects in ZIFs and their glasses ⚠️ With @henkegroup.bsky.social
and the Brunner group @tudresden.bsky.social by NMR we observed that dangling linker imidazoles react with CO2 to form carbamates during adsorption studies - now in Chem. Mater. @acs.org !
pubs.acs.org/doi/10.1021/...

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...

Take a look at Albrechts work in @chemsci.bsky.social @royalsocietypublishing.org A series of electron deficient vinylene-linked COFs was prepared and used to host sulfur in cathodes for LiS 🔋 Financed by CRC-1415 @dfg.de pubs.rsc.org/en/content/a...

Square-triangle tilings could be an infinite topological playground for 2D COFs, but they require precise linker size matching to work. Here we present a system, where we see evidence of linker mixing and heteroepitaxy due to size matching.

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...

To get started on #Bluesky - check out is the new preprint of @knebelalexander.bsky.social on @chemrxiv.bsky.social ! A nominally non-porous MOF MIL-116 was used as a filler in MMMs for separating Helium from Natural Gas! Glad we could contribute to this work!

chemrxiv.org/engage/chemr...