γ -Strontium carbodiimide, γ-SrNCN, was synthesized from a mixture of strontium subnitride (Sr 2 N) and tetracyanoethylene (C 6 N 4 ) at 38 (3) GPa in a laser-heated diamond anvil cell. Its crystal structure was solved and refined using synchrotron single-crystal X-ray diffraction. The new polymorph crystallizes in space group I 4/ mcm (No. 140), where the Sr 2+ and NCN 2− packing can be derived from the CsCl (B2) structure type. γ -SrNCN ( tI 16-SrNCN) is isostructural to tI 16-BaNCN and represents the first high-pressure polymorph of SrNCN.

The NMR interaction tensors of 9 Be and 11 B of hambergite, BeBOOH, were derived from single‐crystal NMR experiments. In the orthorhombic crystal structure of hambergite (which we redetermined by single‐crystal XRD, confirming the results of previous studies), both beryllium and boron atoms occupy Wyckoff position , with atoms pairwise related by inversion symmetry. This leads to four magnetically independent 9 Be and 11 B atoms per site, which are observable in the NMR spectra. Unequivocal assignment of these resonances to atomic positions in the unit cell is generally impossible, as an analysis of the symmetry relations shows. For the hambergite system, this assignment ambiguity could be resolved with the help of DFT calculations using the VASP code, with the resulting eigenvectors compared with the experimental ones. Examination of 9 Be– 1 H dipolar coupling effects, which could be detected in some of the 9 Be spectra, in combination with XRD experiments to confirm the goniometer axis orientation, provided further spatial information and confirmed the assignment. The thus determined numerical values for the quadrupolar coupling constants and isotropic chemical shifts are as follows: for 9 Be[1] kHz and 1.6 ppm, for 9 Be[2] kHz and 1.4 ppm and for 11 B[1] MHz and 18.1 ppm.

Organic cations can directly contribute to the electronic structure in hybrid organic-inorganic (HOI) materials, resulting in the formation of charge transfer semiconductors. Systematic tuning of the band gap by varying the organic cation in HOI charge transfer semiconductors remains underexplored. Here, we report the synthesis and characterization of (phenH(2))SbCl5 (phenH(2) = 1,10-phenanthrolinium) and investigate how the extended pi-system influences optical properties compared to the previously reported (2,2-bpyH(2))SbCl5 (2,2-bpyH(2) = 2,2 '-bipyridinium). Both compounds feature tetrameric [Sb4Cl20](8-) units and exhibit charge-transfer band gaps. Diffuse-reflectance spectroscopy shows a red-shifted absorption onset for (phenH(2))SbCl5 relative to (2,2-bpyH(2))SbCl5. The band gap decreases from 2.6 eV in (2,2-bpyH(2))SbCl5 to 2.1 eV in (phenH(2))SbCl5, a reduction of >0.4 eV. Density-functional theory (DFT) calculations indicate that this red-shift arises from increased contribution of the phenanthroline pi*-orbitals to the conduction band. This demonstrates that systematic variation of the organic cation's pi-conjugation can provide a strategy for band gap tuning in charge-transfer HOI antimony halides.

ABSTRACT Inorganic antiperovskites with the formula X 3 A N ( X = Ba, Sr, Ca, Mg; A = As, Sb) have recently been reported to exhibit excellent optoelectronic properties including small carrier effective masses, suitable direct bandgaps, high optical absorption coefficients as well as allowed optical transitions at the band edges. Using the ammonothermal method, we have synthesized the imide antiperovskites AE 5 Pn 2 (NH) 2 ( AE = Ca, Sr; Pn = As, Sb, Bi). The crystal structures of AE 5 Pn 2 (NH) 2 were solved and refined in the orthorhombic space group Pbam by single‐crystal x‐ray diffraction (scXRD), and further confirmed using powder X‐ray diffraction (pXRD) and Raman spectroscopy. Depending on the ion size ratio between AE 2+ and Pn 3– , different degrees of octahedral tilting can be observed. Soft X‐ray spectroscopy was used to study the band gap and electronic structure, and revealed the presence of oxygen impurities. The AE 5 Pn 2 (NH) 2 compounds can further react to form the ternary antiperovskites AE 3 Pn N. Density functional theory calculations reveal favorable transport and optical properties. Narrow direct band gaps in the range of 0.87–1.76 eV could be verified experimentally, making AE 5 Pn 2 (NH) 2 not only suitable as precursor materials for the corresponding AE 3 Pn N antiperovskites, but also as promising candidates for solar cell absorber materials.

This study reports the synthesis of two rare-earth imidonitridophosphates and a series of 3d transition metal imidonitridophosphates (MIIIH3P6N12 with M = V, Cr, Eu, Lu, and MIIH4P6N12 with M = Mn, Fe, Co, Ni) by high-pressure metathesis. The crystal structures were elucidated by a combination of single-crystal and powder X-ray diffraction, elemental analysis, and vibrational spectroscopy. All compounds crystallize in the orthorhombic crystal system (transition metal imidonitridophosphates: Cmce, EuH3P6N12: Pna21, LuH3P6N12: Pbam) and feature a layered anionic network composed of vertex-sharing [PN4] tetrahedra. Magnetic measurements indicated that Mn, Fe, Co, and Ni are in the oxidation state + II, while V, Cr, Eu, and Lu are in the oxidation state + III. Furthermore, the measurements revealed paramagnetic behavior for all compounds except LuH3P6N12 and indications of antiferromagnetic ordering at low temperatures for NiH4P6N12 and CrH3P6N12. The oxidation states of Fe and Eu were further confirmed by Mössbauer spectroscopic measurements. As LuH3P6N12 does not exhibit paramagnetic behavior, additional NMR spectroscopic measurements were conducted. Furthermore, luminescence measurements provided information that supported the structural characterization and gave insights into the ligand field strength of the coordination sphere of the metal atoms in the considered imidonitridophosphates, indicating that the [PN4] units show weakened coordination behavior.

Melam and ammeline are simple, s-triazine-based compounds first described by Liebig nearly 200 years ago. Outgoing from these two compounds, synthetic strategies for asymmetrically substituted s-triazines were developed. As the initial key step, Clauson-Kaas pyrrolation of the compounds' primary amino groups was carried out, significantly improving their solubility in organic solvents and thereby facilitating further conversions. These include functionalization of the s-triazine bridging amino group of pyrrolated melam by reaction with electrophiles, while pyrrolated ammeline was deoxychlorinated and subsequently reacted with nucleophiles to displace the resulting Cl substituent. Moreover, a reaction protocol for reversion of pyrrolyl into amino groups was developed, which involved ozonolysis, followed by treatment with aqueous NaOCl of the resulting formamide derivatives. Thereby, melam derivatives with essentially the same coordination site but enhanced solubilities were obtained. This enabled the preparation of a Cu(II) coordination complex from aqueous solution, which is unheard of for melam itself. Finally, the thus accessible s-triazines were structurally characterized to gain deeper insights on how the different conducted transformations influence the physicochemical properties relevant for future applications.

The NMR interaction tensors of 9Be and 11B of hambergite, Be 2 BO 3 OH, were derived from single-crystal NMR experiments. In the orthorhombic crystal structure of hambergite (which we redetermined by single-crystal XRD, confirming the results of previous studies), both beryllium and boron atoms occupy Wyckoff position 8 c , with atoms pairwise related by inversion symmetry. This leads to four magnetically independent 9Be and 11B atoms per site, which are observable in the NMR spectra. Unequivocal assignment of these resonances to atomic positions in the unit cell is generally impossible, as an analysis of the symmetry relations shows. For the hambergite system, this assignment ambiguity could be resolved with the help of DFT calculations using the VASP code, with the resulting eigenvectors compared with the experimental ones. Examination of 9Be-1H dipolar coupling effects, which could be detected in some of the 9Be spectra, in combination with XRD experiments to confirm the goniometer axis orientation, provided further spatial information and confirmed the assignment. The thus determined numerical values for the quadrupolar coupling constants χ and isotropic chemical shifts δ i s o are as follows: for 9Be[1] 222 . 6 ± 0 . 6  kHz and 1.6 ppm, for 9Be[2] - 121 . 2 ± 0 . 4  kHz and 1.4 ppm and for 11B[1] 2 . 648 ± 0 . 004  MHz and 18.1 ppm.

Phosphor-converted light-emitting diodes (pc-LEDs) are a key technology in the reduction of global energy consumption. The understanding of the chemical and electronic properties of eligible substance classes is essential for applications of pc-LEDs. Here, the electronic structure, band gap, and band structure of highly condensed Eu2+-doped nitrodoberyllosilicates, MBeSi2N4:Eu2+ (M = Ca, Sr) are studied using synchrotron-based soft X-ray absorption spectroscopy (XAS) and emission spectroscopy (XES) as well as density functional theory (DFT). The electronic band gaps for MBeSi2N4:Eu2+ are determined to be 4.20 +/- 0.25 eV for M = Ca and 4.30 +/- 0.25 eV for M = Sr using the combination of XAS and XES measurements. The measured band gap is in excellent agreement with our calculations (4.60 eV for M = Ca and 4.80 eV for M = Sr) using the Perdew-Burke-Ernzerhof variant of the generalized gradient functional, including a semilocal potential modified from that of Becke and Johnson. Based on the DFT calculations and the measurements, it is found that both compounds exhibit direct band gap transitions. The calculated partial density of states reveal that the N p-states dominate in the valence band for both materials, and the Ca d-states and Sr d-states dominate in the conduction band of CaBeSi2N4 and SrBeSi2N4, respectively. The observed electronic band gap is large enough, which will not interfere with the luminescent transition of 5d -> 4f of Eu2+ emission. Thus, these two materials are promising candidates as host materials in pc-LEDs applications.

For the activation of nitrogen and its reduction to ammonia, transition metals are crucial in biological as well as industrial processes. So far, only a few binary transition metal compounds with nitrogen dimer anions are known, whereas a ternary compound has remained undiscovered as yet. Here, we report on the synthesis and properties of the first ternary transition metal compound, namely, BeW10N14(N2), which exhibits dinitrogen anions. It was synthesized in a high-temperature high-pressure approach from W2Be4N5. The crystal structure, elucidated with synchrotron radiation, unites WN7 capped trigonal prisms with intriguing BeN6 octahedra and (N2)-anions. Elastic and electronic properties of the title compound were corroborated by DFT calculations, revealing simultaneous ultra-incompressible and metallic behavior. The synthesis and investigation of the first ternary transition metal nitride with dinitrogen units opens the door to a new field of research on nitride and pernitride chemistry.

In exploring advanced materials for solar power, the novel titanium nitridophosphate (TiP4N8) stands out due to its unique linear nitrogen bridging. To investigate the elemental interactions responsible for the photovoltaic performance under visible light, the titanium L2, 3-edges and nitrogen K-edge are specifically explored using X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES), and resonant inelastic X-ray scattering (RIXS) techniques to map the unoccupied and occupied electronic states. It is shown that the indirect interaction between the linear nitrogen bearing the lone pair and titanium is responsible for the bandgap of 1.55 ± 0.30 eV and 1.77 ± 0.30 eV in the β- and α-TiP4N8 phases as well as the stability of the α-phase. The formal oxidation state of the Ti ion in the β- and α-phases are also validated to be trivalent (Ti+3) and both trivalent (Ti+3) and tetravalent (Ti+4), respectively.

In this study, the electronic structure and bonding characteristics of PTaN (x = 0.1-0.15), a compound featuring a high coordination of phosphorus with six nitrogen atoms, are explored. Soft X-ray spectroscopy and density functional theory calculations are employed to investigate the material's electronic properties. The analysis reveals that the material exhibits metallic behavior, which can be attributed to the 5d electronic states of tantalum. It is observed that tantalum exists in mixed valence states, forming two distinct types of Ta-N bonds: one predominantly covalent and the other with a combination of ionic and covalent characteristics. Both bond types contribute to the metallic properties observed. Additionally, it is found that the valence electrons of tantalum are not fully integrated into the Ta-N bonds, as supported by electron localization function (ELF) calculations, which show electron localization in narrow channels consisting of three Ta atoms. To the best of our knowledge, we have measured the phosphorus L beta 3,beta 4 XES and L1-edge XAS for the first time. These findings enhance one's understanding of the complex electronic structure of PTaN and provide insights into the material's potential applications in electronic devices and electrocatalysis.

Ammelide, also known as melanuric acid, is a simple molecular compound, which can be regarded as the double hydrolysis product of the industrially relevant compound melamine. Within this work, the first structural description of ammelide was provided almost 200 years after its discovery. This not only gave the first unambiguous evidence that ammelide's preferred tautomeric form in the solid is 6-amino-1,3,5-triazine-2,4(1H,3H)-dione, but also showed that ammelide adopts a layered structure similar to the closely related ammeline. Moreover, the crystal structures of three modifications of the 1:1 adduct between ammeline and ammelide were elucidated, which form layers with a honeycomb motif and hexagonal voids analogous to melamine cyanurate. Differential thermal analysis and thermogravimetric analysis demonstrated that both pure ammelide and its adduct with ammeline have exceptionally high thermal stabilities, resulting from their dense hydrogen bonding networks. Finally, the synthesis and structural characterization of the ammelide's nitrate and perchlorate salts were carried out to examine the potential of ammelide as part of insensitive high-energy-density materials through sensitivity measurements and theoretical calculations.

Monomeric s-heptazines are an intriguing class of compounds with many attractive properties for various areas of application such as photocatalysis or organic light-emitting diodes. However, research into these properties has so far been challenging, as only a few synthetic routes for the preparation of monomeric s-heptazines are known in the literature. Furthermore, these few reported synthetic pathways generally require the use of specialized equipment that may not be available to all laboratories interested in studying monomeric s-heptazines. For this reason, a more accessible synthetic route for the preparation of monomeric s-heptazines has been developed in the course of this work. The central compound of this new approach is 2,5,8-tri(1H-pyrrol-1-yl)-s-heptazine, which could be conveniently synthesized via an acid catalyzed pyrrolation of melem with bench-stable 2,5-dimethoxytetrahydrofuran in a simple one-pot synthesis in air. This compound was shown to be a potent starting material for the synthesis of numerous other monomeric s-heptazines by reaction with both nucleophiles and electrophiles. The monomeric s-heptazines thus accessible were analyzed for their crystal structures by single crystal X-ray diffraction and for their optical properties by ultraviolet/visible and photoluminescence spectroscopy.

A main challenge for the operation of a nuclear fusion reactor is the consumption of tritium during the fusion process and the limited availability of tritium in natural resources or its production in nuclear power plants. The most promising approach is breeding of new tritium within the operating fusion reactor. For this purpose, suitable breeding materials are needed. Lithium beryllium oxides are a promising class of compounds, as they unite both target and neutron multiplier in one material. While there have already been studies on sintered ceramics in the Li2O·BeO system, the crystal structure of compounds of a defined composition has so far remained unsolved. Herein, we report on the synthesis of phase-pure Li2Be2O3 in a high-temperature (HT) approach and its structure determination by single-crystal X-ray diffraction (sc-XRD). In addition, the compound was characterized by powder X-ray diffraction (PXRD), solid-state nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. The thermal stability, which is important for use as blanket material in a fusion reactor, was examined with differential scanning calorimetry (DSC).

In this work, we present a comprehensive study of the luminescence relaxation mechanism and the associated spectral broadening in a series of Eu2+-doped narrow-band phosphors. It is highlighted that the commonly used full-width at half-maximum (fwhm) is no longer a sensitive measure for quantifying the emission bandwidth of these materials. A thorough understanding of the factors contributing to the narrow bandwidth requires an explicit treatment of the magnetic structure of the ground and emissive excited state manifolds. This requires incorporating spin-orbit coupling effects using wave function-based methods such as the complete active space self-consistent field combined with second-order N-electron valence state perturbation theory (CASSCF/NEVPT2). In addition, for the associated excited state dynamics calculations, one needs to consider vibronic coupling interactions on the basis of Franck-Condon (FC), Herzberg-Teller (HT), and, when necessary, pseudo Jahn-Teller (PJT) coupling effects. Our analysis underscores that understanding and controlling the synergistic roles of these "static" and "dynamic" effects are essential for accurately assessing the narrow band emission relaxation in these systems. We show that these results can, in principle, be generalized to an arbitrary set of narrow-band phosphor candidates and can potentially aid the experimental efforts toward developing novel phosphors with enhanced luminescent properties.

Highly condensed alkaline earth nitridophosphates have attracted increasing scientific interest, due to their high thermal and chemical stability, as well as their promising luminescence behavior upon doping with Eu2+ for pc-LED applications. In particular, the barely explored mixed tetrahedra-based nitridophosphates offer a wide range of structural and compositional diversity, enabling new insights into structure-property relationships. Herein, we report on the first quaternary alkaline earth nitridoborophosphate Ba2BP7N14, synthesized at 8 GPa and 1600 °C in a multianvil press, starting from Ba(N3)2, h-BN and P3N5. Ba2BP7N14 crystallizes in the barylite-1O polytype and features a highly condensed mixed (B,P)-N anionic 3D network (κ≈0.57) built up of PN4 and mixed occupied (P0.75B0.25)N4 tetrahedra. The structure was characterized by a multi-step process involving single-crystal and powder X-ray diffraction (SCXRD, PXRD), elemental analysis, electron microscopy (STEM, EELS), and solid-state 31P and 11B MAS NMR spectroscopy. The plausibility of the structural model was corroborated by low-cost crystallographic calculations. The optical band gap and the thermal behavior of an undoped sample of Ba2BP7N14, were determined from diffuse reflectance spectroscopy and temperature-dependent powder X-ray diffraction, respectively. Irradiation of a Eu2+-doped sample with near-UV light results in a blue emission peaking at λem=422 nm.

An abundance of oxide, halide and chalcogenide perovskites have been explored, demonstrating outstanding properties, while the emerging nitride perovskites are extremely rare due to their challenging synthesis requirements. By inverting the ion type in the perovskite structure, the corresponding antiperovskite structure is obtained. Among them, ternary antiperovskite nitrides X3AN (X=Ba, Sr, Ca, Mg; A=As, Sb) have recently been identified as exhibiting excellent optoelectronic properties. To explore the unrealized composition space of nitride perovskites, the ammonothermal method was applied, yielding three new layered quaternary imide-based defect-antiperovskites, namely AE5AsPn(NH)2 (AE=Ca, Sr; Pn=Sb, Bi). These new compounds feature distorted square-pyramidal coordination around the imide-group (Ca5NH). Layers with Ca2+ vacancies are found with an alternating As3- and Pn3- (Pn3-=Sb3-, Bi3-) coordination along the A-site, forming a two-dimensional (2D) structure. All three AE5AsPn(NH)2 compounds show suitable direct band gaps within the visible light spectrum. Density functional theory calculations reveal favorable band dispersion, as well as transport and optical properties, especially along the out-of-plane direction, demonstrating their 3D character of electronic transport. The narrow tunable direct band gaps and favorable charge carrier properties make AE5AsPn(NH)2 promising candidates for solar cell absorber materials.

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 β‐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.

High-pressure, high-temperature (HP/HT) syntheses are essential for modern high-performance materials. Phosphorus nitride, nitridophosphate, and more generally nitride syntheses benefit greatly from HP/HT conditions. In this contribution, we present the first systematic in situ investigation of a nitridophosphate HP/HT synthesis using the reaction of zinc nitride Zn3N2 and phosphorus(V) nitride P3N5 to the nitride semiconductor Zn2PN3 as a case study. At a pressure of 8 GPa and temperatures up to 1300 °C, the reaction was monitored by energy-dispersive powder X-ray diffraction (ED-PXRD) in a large-volume press at beamline P61B at DESY. The experiments investigate the general behavior of the starting materials under extreme conditions and give insight into the reaction. During cold compression and subsequent heating, the starting materials remain crystalline above their ambient-pressure decomposition points, until a sufficient minimum temperature is reached and the reaction starts. The reaction proceeds via ion diffusion at grain boundaries with an exponential decay in the reaction rate. Raising the temperature above the minimum required value quickly completes the reaction and initiates single-crystal growth. After cooling and decompression, which did not influence the resulting product, the recovered sample was analyzed by energy-dispersive X-ray (EDX) spectroscopy.

Ternary nitride semiconductors are rapidly emerging as a promising class of materials for energy conversion applications, offering an appealing combination of strong light absorption in the visible range, desirable charge transport characteristics, and good chemical stability. In this work, it is shown that finite-temperature lattice dynamics in CuTaN2 - a prototypical ternary nitride displaying particularly strong visible light absorption - exhibit a pronounced anharmonic character that plays an essential role in defining its macroscopic optoelectronic and thermal properties. Low-frequency vibrational modes that are Raman-inactive from symmetry considerations of the average crystal structure and unstable in harmonic phonon calculations are found to appear as intensive Raman features near room temperature. The atomic contributions to the anharmonic vibrations are characterized by combining Raman measurements with molecular dynamics and density functional theory calculations. This analysis reveals that anharmonic lattice dynamics have large ramifications on the fundamental properties of this compound, resulting in uniaxial negative thermal expansion and the opening of its bandgap to a near-optimal value for solar energy harvesting. The atomic-level understanding of anharmonic lattice dynamics, as well as the finding that they strongly influence key properties of this semiconductor at room temperature, have important implications for design of new functional materials, especially within the emerging class of ternary nitride semiconductors.