Synthesis and Comprehensive Studies of Be-IV-N2 (IV = Si, Ge): Solving the Mystery of Wurtzite-Type Pmc21 Structures.

The research for wurtzite-type ternary nitride semiconductors containing earth abundant elements with a stoichiometry of 1:1:2 was focused on metals like Mg or Zn, so far. The vast majority of these Grimm-Sommerfeld analogous compounds crystallize in the ß-NaFeO2 structure, although a second arrangement in space group Pmc21 is predicted to be a viable alternative. Despite extensive theoretical and experimental studies, this structure has so far remained undiscovered. Herein, we report on BeGeN2 in a Pmc21 structure, synthesized from Be3N2 and Ge3N4 using a high-pressure high-temperature approach at 6 GPa and 800 °C. The compound was characterized by powder X-ray diffraction (PXRD), solid state nuclear magnetic resonance (NMR), Raman and energy dispersive X-ray (EDX) spectroscopy, temperature-dependent PXRD, second harmonic generation (SHG) and UV/VIS measurements and in addition also compared to its lighter homologue BeSiN2 in all mentioned analytic techniques. The synthesis and investigation of both the first beryllium germanium nitride and the first ternary wurtzite-type nitride crystallizing in space group Pmc21 open the door to a new field of research on wurtzite-type related structures.

Mixed Tin Valence in the Tin(II/IV)-Nitridophosphate Sn3P8N16.

Sn3P8N16 combines the structural versatility of nitridophosphates and Sn within one compound. It was synthesized as dark gray powder in a high-pressure high-temperature reaction at 800 °C and 6 GPa from Sn3N4 and P3N5. The crystal structure was elucidated from single-crystal diffraction data (space group C2/m (no. 12), a=12.9664(4), b=10.7886(4), c=4.8238(2) Å, ß=109.624(1)°) and shows a 3D-network of PN4 tetrahedra, incorporating Sn in oxidation states +II and +IV. The Sn cations are located within eight-membered rings of vertex-sharing PN4 tetrahedra, stacked along the [001] direction. A combination of solid-state nuclear magnetic resonance spectroscopy, 119Sn Mössbauer spectroscopy and density functional theory calculations was used to confirm the mixed oxidation of Sn. Temperature-dependent powder X-ray diffraction measurements reveal a low thermal expansion of 3.6 ppm/K up to 750 °C, beyond which Sn3P8N16 starts to decompose.

Trigonal Planar [PN3]4- Anion in the Nitridophosphate Oxide Ba3[PN3]O.

Nitridophosphates, with their primary structural motif of isolated or condensed PN4 tetrahedra, meet many requirements for high performance materials. Their properties are associated with their structural diversity, which is mainly limited by this specific building block. Herein, we present the alkaline earth metal nitridophosphate oxide Ba3[PN3]O featuring a trigonal planar [PN3]4- anion. Ba3[PN3]O was obtained using a hot isostatic press by medium-pressure high-temperature synthesis (MP/HT) at 200 MPa and 880 °C. The crystal structure was solved and refined from single-crystal X-ray diffraction data in space group R 3 ‾ ${\bar 3}$ c (no. 167) and confirmed by SEM-EDX, magic angle spinning (MAS) NMR, vibrational spectroscopy (Raman, IR) and low-cost crystallographic calculations (LCC). MP/HT synthesis reveals great potential by extending the structural chemistry of P to include trigonal planar [PN3]4- motifs.

On Tautomerism and Amphoterism: An In-Depth Structural and Physicochemical Characterization of Ammeline and Some of Its Salts.

Ammeline is a simple, readily available, molecular compound, which has been known for nearly 200 years. Despite that, no proper structural characterization of ammeline has been conducted so far. For this reason, the prevalent tautomeric form of ammeline in the solid remained unknown to this date. In the course of this study, its crystal structure was finally established by single-crystal X-ray diffraction. In this structure, ammeline is exclusively found as its 4,6-diamino-1,3,5-triazin-2(1H)-one tautomer and adopts layered structure with an exceptionally high hydrogen bond density. Ammeline shows an interesting amphoteric behavior. Therefore, the synthesis and structural characterization of some of its salts were carried out to investigate the influence of the protonation degree on its molecular structure. In particular, the crystal structure of silver ammelinate monohydrate was solved as the first reported structure containing deprotonated ammeline. Moreover, the crystal structures of three different modifications of ammelinium perchlorate were elucidated and the transformation conditions between them were studied. Lastly, the crystal structure of ammelinediium diperchlorate monohydrate, containing unprecedented doubly protonated ammeline, was determined. The products' thermal behavior was studied by differential thermal analysis and thermogravimetric analysis. The perchlorate salts were additionally examined for their potential as insensitive high-energy-density materials.

Highly Condensed and Super-Incompressible Be2PN3.

Although beryllium and its compounds show outstanding properties, owing to its toxic potential and extreme reaction conditions the chemistry of Be under high-pressure conditions has only been investigated sparsely. Herein, we report on the highly condensed wurtzite-type Be2PN3, which was synthesized from Be3N2 and P3N5 in a high-pressure high-temperature approach at 9 GPa and 1500 °C. It is the missing member in the row of formula type M2PN3 (M = Mg, Zn). The structure was elucidated by powder X-ray diffraction (PXRD), revealing that Be2PN3 is a double nitride, rather than a nitridophosphate. The structural model was further corroborated by 9Be and 31P solid-state nuclear magnetic resonance (NMR) spectroscopy. We present 9Be NMR data for tetrahedral nitride coordination for the first time. Infrared and energy-dispersive X-ray spectroscopy (FTIR and EDX), as well as temperature dependent PXRD complement the analytical characterization. Density functional theory (DFT) calculations reveal super-incompressible behavior and the remarkable hardness of this low-density material. The formation of Be2PN3 through a high-pressure high-temperature approach expands the synthetic access to Be-containing compounds and may open access to various multinary beryllium nitrides.

Building Nitridic Networks with Phosphorus and Germanium-from GeIIP2N4 to GeIVPN3.

Nitridophosphates and nitridogermanates attract high interest in current research due to their structural versatility. Herein, the elastic properties of GeP2N4 were investigated by single-crystal X-ray diffraction (XRD) upon compression to 44.4(1) GPa in a diamond anvil cell. Its isothermal bulk modulus was determined to be 82(6) GPa. At 44.4(1) GPa, laser heating resulted in the formation of multiple crystalline phases, one of which was identified as unprecedented germanium nitridophosphate GePN3. Its structure was elucidated from single-crystal XRD data (C2/c (no. 15), a = 8.666(5), b = 8.076(4), c = 4.691(2) Å, ß = 101.00(7)°) and is built up from layers of GeN6 octahedra and PN4 tetrahedra. The GeN6 octahedra form double zigzag chains, while the PN4 tetrahedra are found in single zigzag chains. GePN3 can be recovered to ambient conditions with a unit cell volume increase of about 12%. It combines PV and GeIV in a condensed nitridic network for the first time.

Tunable Narrow-Band Cyan-Emission of Eu2+-doped Nitridomagnesophosphates Ba3-xSrx[Mg2P10N20] : Eu2+ (x=0-3).

Tetrahedron-based nitrides offer a wide range of properties and applications. Highly condensed nitridophosphates are examples of nitrides that exhibit fascinating luminescence properties when doped with Eu2+, making them appealing for industrial applications. Here, we present the first nitridomagnesophosphate solid solution series Ba3-xSrx[Mg2P10N20] : Eu2+ (x=0-3), synthesized by a high-pressure high-temperature approach using the multianvil technique (3 GPa, 1400 °C). Starting from the binary nitrides P3N5 and Mg3N2 and the respective alkaline earth azides, we incorporate Mg into the P/N framework to increase the degree of condensation κ to 0.6, the highest observed value for alkaline earth nitridophosphates. The crystal structure was elucidated by single-crystal X-ray diffraction, powder X-ray diffraction, energy-dispersive X-ray spectroscopy (EDX), and solid-state NMR. DFT calculations were performed on the title compounds and other related highly condensed nitridophosphates to investigate the influence of Mg in the P/N network. Eu2+-doped samples of the solid solution series show a tunable narrow-band emission from cyan to green (492-515 nm), which is attributed to the preferred doping of a single crystallographic site. Experimental confirmation of this assumption was provided by overdoping experiments and STEM-HAADF studies on the series as well on the stoichiometric compound Ba2Eu[Mg2P10N20] with additional atomic resolution energy-dispersive X-ray spectroscopy (EDX) mapping.

Reduction of Germanium Oxides-The Mixed-Valence Germanates A2Ge4O7 (A = Na, K).

We report on the synthesis of two-layered alkali germanates, Na2Ge4O7 and K2Ge4O7. Both compounds were synthesized by using the ammonothermal method at 823 K and 100 MPa. Under these conditions, germanium is partially reduced from the +IV state to +II, forming mixed-valence compounds with the rarely observed [Ge(II)O3]4- unit. The valence state was verified by X-ray photoelectron spectroscopy (XPS) and was accompanied by theoretical calculations alongside vibrational spectroscopy and single-crystal X-ray structure determination. The compounds crystallize in the trigonal space groups (Na2Ge4O7: P3̅c1 and K2Ge4O7: P3̅m1) and feature layers of corner sharing [Ge(II)O3]4- and [Ge(IV)2O7]6- units forming [Ge(II)2Ge(IV)2O7]2- polyanions. These layers are separated by alkali metal ions. The compounds are colorless insulators with band gaps of 4.0-4.2 eV. According to the Robin-Day classification, both compounds can be described as class I materials, where the valences are trapped on specific sites.

The Fundamental Disorder Unit in (Si, P)-(O, N) Networks.

This study presents the synthesis and characterization of oxonitridosilicate phosphates Sr3SiP3O2N7, Sr5Si2P4ON12, and Sr16Si9P9O7N33 as the first of their kind. These compounds were synthesized under high-temperature (1400 °C) and high-pressure (3 GPa) conditions. A unique structural feature is their common fundamental building unit, a vierer single chain of (Si, P)(O, N)4 tetrahedra. All tetrahedra comprise substitutional disorder which is why we refer to it as the fundamental disorder unit (FDU). We classified four different FDU motifs, revealing systematic bonding patterns. Including literature known Sr5Si2P6N16, three of the four patterns were found in the presented compounds. Common techniques like single-crystal X-ray diffraction (SCXRD), elemental analyses, and 31P nuclear magnetic resonance (NMR) spectroscopy were utilized for structural analysis. Additionally, low-cost crystallographic calculations (LCC) provided insights into the structure of Sr16Si9P9O7N33 where NMR data were unavailable due to the lack of bulk samples. The optical properties of these compounds, when doped with Eu2+, were investigated using photoluminescence excitation (PLE), photoluminescence (PL) measurements, and density functional theory (DFT) calculations. Factors influencing the emission properties, including thermal quenching mechanisms, were discussed. This research reveals the new class of oxonitridosilicate phosphates with unique systematic structural features that offer potential for theoretical studies of luminescence and band gap tuning in insulators.

Chemical and Physical Properties of YHg3 and LuHg3.

Amalgams have played an important role in fundamental and applied solid-state chemistry and physics because of the diversity of crystallographic features and properties that they have to offer. Moreover, their peculiar chemical properties can sometimes give rise to unconventional superconducting or magnetic ground states. In the current work, we present an in-depth analysis of single crystals of YHg3 and LuHg3 (Mg3Cd structure type, space group P63/mmc). Both compounds show superconductivity below Tc = 1 ± 0.1 K (YHg3) and Tc = 1.2 ± 0.1 K (LuHg3). Given the high air-sensitivity and toxicity of these compounds, this study was only possible using a number of dedicated experimental techniques.

Crystal Chemistry and Physics of UCd11.

In the phase diagram U-Cd, only one compound has been identified so far─UCd11 (space group Pm3̅m). Since the discovery of this material, the physical properties of UCd11 have attracted a considerable amount of attention. In particular, its complex magnetic phase diagram─as a result of tuning with magnetic field or pressure─is not well-understood. From a chemical perspective, a range of lattice parameter values have been reported, suggesting a possibility of a considerable homogeneity range, i.e., UCd11-x. In this work, we perform a simultaneous study of crystallographic features coupled with measurements of physical properties. This work sheds light on the delicate relationship between the intrinsic crystal chemistry and magnetic properties of UCd11.

BaGe8As14: a semiconducting sodalite-type compound.

A new sodalite-type compound, namely BaGe8As14 was synthesized via solid-state reactions and structurally characterized with single crystal X-ray diffraction (space group I4[combining macron]3m). Vertex-sharing GeAs4-tetrahedra form ß-cages with additional Ge/As-mixed sites located slightly above or below the six-membered rings. The structure is similar to the borate mineral rhodizite. Barium atoms are disordered due to a slight shift off the centers of large ß-cages. This partially disordered structure together with a narrow bandgap of 0.43 eV in line with low resistivity (2 × 10-2Ω cm), and a high carrier concentration (1.6 × 1020 cm-3) at 300 K qualifies BaGe8As14 as a potential thermoelectric material.

Mixed Valence and Unusual Germanium Coordination in SrGe8As10, BaGe8As10, and BaGe7P12.

The new Zintl-compounds AEGe8As10 (AE = Sr, Ba) and BaGe7P12 were synthesized via solid-state reactions, and their structures were determined by single crystal and powder X-ray diffraction. SrGe8As10 and BaGe8As10 crystallize in the space group Cmce and show complex 3D networks composed of three different Ge-As motifs and As-As bonds with mixed valence of germanium in the oxidation states +2, + 3, and +4. Mixed valences of germanium +3 and +4 occur in BaGe7P12, which crystallizes in the space group R3̅ with a 3D network built up of Ge2P6 dumbbells and P-P bonds. An exceptional 6-fold coordinated germanium resides in the center of a GeP6 trigonal antiprism. High temperature X-ray diffraction shows thermal stabilities up to 923-953 K. UV-Vis and resistivity measurements reveal a semiconducting nature with small indirect band gaps between 0.02 and 1.6 eV. Electronic band structure calculations confirm the semiconducting state and indicate covalent bonds within the Ge-Pn polyanions.