Li₁₀SnP₂S₁₂: An Affordable Lithium Superionic Conductor

The reaction of Li₂S and P₂S₅ with Li₄[SnS₄], a recently discovered, good Li⁺ ion conductor, yields Li₁₀SnP₂S₁₂, the thiostannate analogue of the record holder Li₁₀GeP₂S₁₂ and the second compound of this class of superionic conductors with very high values of 7 mS/cm for the grain conductivity and 4 mS/cm for the total conductivity at 27 °C. The replacement of Ge by Sn should reduce the raw material cost by a factor of ∼3

Li₁₀SnP₂S₁₂: An Affordable Lithium Superionic Conductor

The reaction of Li₂S and P₂S₅ with Li₄[SnS₄], a recently discovered, good Li⁺ ion conductor, yields Li₁₀SnP₂S₁₂, the thiostannate analogue of the record holder Li₁₀GeP₂S₁₂ and the second compound of this class of superionic conductors with very high values of 7 mS/cm for the grain conductivity and 4 mS/cm for the total conductivity at 27 °C. The replacement of Ge by Sn should reduce the raw material cost by a factor of ∼3

Highly Active Iron Catalyst for Ammonia Borane Dehydrocoupling at Room Temperature

The iron complex [FeH­(CO) (PNP)] (PNP = N­(CH₂CH₂P<i>i</i>Pr₂)₂) is a highly active catalyst for ammonia borane dehydrocoupling at room temperature. Mainly linear polyaminoborane is obtained upon release of 1 equiv of H₂. Mechanistic studies suggest that both hydrogen release and B–N coupling are metal-catalyzed and proceed via free aminoborane. Catalyst deactivation results from reaction with free BH₃ that is formed by aminoborane rearrangement. Importantly, borane trapping with a simple amine allows for the observation of a TON that is unprecedented for a well-defined base metal catalyst

Nonequilibrium Catalyst Materials Stabilized by the Aerogel Effect: Solvent Free and Continuous Synthesis of Gamma-Alumina with Hierarchical Porosity

Heterogeneous catalysis can be understood as a phenomenon which strongly relies on the occurrence of thermodynamically less favorable surface motifs like defects or high-energy planes. Because it is very difficult to control such parameters, an interesting approach is to explore metastable polymorphs of the respective solids. The latter is not an easy task as well because the emergence of polymorphs is dictated by kinetic control and materials with high surface area are required. Further, an inherent problem is that high temperatures required for many catalytic reactions can also induce the transformation to the thermodynamically stable modification. Alumina (Al₂O₃) was selected for the current study as it exists not only in the stable α-form but also as the metastable γ-polymorph. Kinetic control was realized by combining an aerosol-based synthesis approach and a highly reactive, volatile precursor (AlMe₃). Monolithic flakes of Al₂O₃ with a highly porous, hierarchical structure (micro-, meso-, and macropores connected to each other) resemble so-called aerogels, which are normally known only from wet sol–gel routes. Monolothic aerogel flakes can be separated from the gas phase without supercritical drying, which in principle allows for a continuous preparation of the materials. Process parameters can be adjusted so the material is composed exclusively of the desired γ-modification. The γ-Al₂O₃ aerogels were much more stable than they should be, and even after extended (80 h) high-temperature (1200 °C) treatment only an insignificant part has converted to the thermodynamically stable α-phase. The latter phenomenon was assigned to the extraordinary thermal insulation properties of aerogels. Finally, the material was tested concerning the catalytic dehydration of 1-hexanol. Comparison to other Al₂O₃ materials with the same surface area demonstrates that the γ-Al₂O₃ are superior in activity and selectivity regarding the formation of the desired product 1-hexene

Linking ³¹P Magnetic Shielding Tensors to Crystal Structures: Experimental and Theoretical Studies on Metal(II) Aminotris(methylenephosphonates)

The ³¹P chemical shift tensor of the phosphonate group [RC-PO₂(OH)]⁻ is investigated with respect to its principal axis values and its orientation in a local coordinate system (LCS) defined from the P atom and the directly coordinated atoms. For this purpose, six crystalline metal aminotris­(methylenephosphonates), <i>M</i>AMP·<i>x</i>H₂O with <i>M</i> = Zn, Mg, Ca, Sr, Ba, and (2Na) and <i>x</i> = 3, 3, 4.5, 0, 0, and 1.5, respectively, were synthesized and identified by diffraction methods. The crystal structure of water-free BaAMP is described here for the first time. The principal components of the ³¹P shift tensor were determined from powders by magic-angle-spinning NMR. Peak assignments and orientations of the chemical shift tensors were established by quantum-chemical calculations from first principles using the extended embedded ion method. Structure optimizations of the H-atom positions were necessary to obtain the chemical shift tensors reliably. We show that the ³¹P tensor orientation can be predicted within certain error limits from a well-chosen LCS, which reflects the pseudosymmetry of the phosphonate environment

The Mechanism of Borane–Amine Dehydrocoupling with Bifunctional Ruthenium Catalysts

Borane–amine adducts have received considerable attention, both as vectors for chemical hydrogen storage and as precursors for the synthesis of inorganic materials. Transition metal-catalyzed ammonia–borane (H₃N–BH₃, AB) dehydrocoupling offers, in principle, the possibility of large gravimetric hydrogen release at high rates and the formation of B–N polymers with well-defined microstructure. Several different homogeneous catalysts were reported in the literature. The current mechanistic picture implies that the release of aminoborane (e.g., Ni carbenes and Shvo’s catalyst) results in formation of borazine and 2 equiv of H₂, while 1 equiv of H₂ and polyaminoborane are obtained with catalysts that also couple the dehydroproducts (e.g., Ir and Rh diphosphine and pincer catalysts). However, in comparison with the rapidly growing number of catalysts, the amount of experimental studies that deal with mechanistic details is still limited. Here, we present a comprehensive experimental and theoretical study about the mechanism of AB dehydrocoupling to polyaminoborane with ruthenium amine/amido catalysts, which exhibit particularly high activity. On the basis of kinetics, trapping experiments, polymer characterization by ¹¹B MQMAS solid-state NMR, spectroscopic experiments with model substrates, and density functional theory (DFT) calculations, we propose for the amine catalyst [Ru­(H)₂PMe₃{HN­(CH₂CH₂P<i>t</i>Bu₂)₂}] two mechanistically connected catalytic cycles that account for both metal-mediated substrate dehydrogenation to aminoborane and catalyzed polymer enchainment by formal aminoborane insertion into a H–NH₂BH₃ bond. Kinetic results and polymer characterization also indicate that amido catalyst [Ru­(H)­PMe₃{N­(CH₂CH₂P<i>t</i>Bu₂)₂}] does not undergo the same mechanism as was previously proposed in a theoretical study

Thermally Highly Stable Amorphous Zinc Phosphate Intermediates during the Formation of Zinc Phosphate Hydrate

The mechanisms by which amorphous intermediates transform into crystalline materials are still poorly understood. Here we attempt to illuminate the formation of an amorphous precursor by investigating the crystallization process of zinc phosphate hydrate. This work shows that amorphous zinc phosphate (AZP) nanoparticles precipitate from aqueous solutions prior to the crystalline hopeite phase at low concentrations and in the absence of additives at room temperature. AZP nanoparticles are thermally stable against crystallization even at 400 °C (resulting in a high temperature AZP), but they crystallize rapidly in the presence of water if the reaction is not interrupted. X-ray powder diffraction with high-energy synchrotron radiation, scanning and transmission electron microscopy, selected area electron diffraction, and small-angle X-ray scattering showed the particle size (≈20 nm) and confirmed the noncrystallinity of the nanoparticle intermediates. Energy dispersive X-ray, infrared, and Raman spectroscopy, inductively coupled plasma mass spectrometry, and optical emission spectrometry as well as thermal analysis were used for further compositional characterization of the as synthesized nanomaterial. ¹H solid-state NMR allowed the quantification of the hydrogen content, while an analysis of ³¹P­{¹H} C rotational echo double resonance spectra permitted a dynamic and structural analysis of the crystallization pathway to hopeite

Superion Conductor Na_11.1Sn_2.1P_0.9Se₁₂: Lowering the Activation Barrier of Na⁺ Conduction in Quaternary 1–4–5–6 Electrolytes

We report on the first quaternary selenide-based Na⁺ superionic solid electrolyte, Na_11.1Sn_2.1P_0.9Se₁₂ (further denoted as NaSnPSe), which shows virtually the same room temperature Na⁺ ion conductivity (3.0 mS/cm) as the current record holder for sulfide-based systems, Na₁₁Sn₂PS₁₂ (denoted as NaSnPS), but with a considerably lower activation energy of 0.30 eV. Both electrolytes belong to the currently highly topical class of solids comprising group I, IV, V, and VI atoms, which we summarize as 1–4–5–6 electrolytes. Herein, they are compared to each other with regard to their structural characteristics and the resulting ion transport properties. The lower activation energy of Na⁺ ion transport in NaSnPSe is well in line with the results of speed of sound measurements, Raman spectroscopy, bond-valence site energy calculations, and molecular dynamics simulations, all of which point to a lower lattice rigidity and to weaker Na–chalcogen interactions as compared to NaSnPS

Superion Conductor Na_11.1Sn_2.1P_0.9Se₁₂: Lowering the Activation Barrier of Na⁺ Conduction in Quaternary 1–4–5–6 Electrolytes

We report on the first quaternary selenide-based Na⁺ superionic solid electrolyte, Na_11.1Sn_2.1P_0.9Se₁₂ (further denoted as NaSnPSe), which shows virtually the same room temperature Na⁺ ion conductivity (3.0 mS/cm) as the current record holder for sulfide-based systems, Na₁₁Sn₂PS₁₂ (denoted as NaSnPS), but with a considerably lower activation energy of 0.30 eV. Both electrolytes belong to the currently highly topical class of solids comprising group I, IV, V, and VI atoms, which we summarize as 1–4–5–6 electrolytes. Herein, they are compared to each other with regard to their structural characteristics and the resulting ion transport properties. The lower activation energy of Na⁺ ion transport in NaSnPSe is well in line with the results of speed of sound measurements, Raman spectroscopy, bond-valence site energy calculations, and molecular dynamics simulations, all of which point to a lower lattice rigidity and to weaker Na–chalcogen interactions as compared to NaSnPS