Rivalry under Pressure: The Coexistence of Ambient‐Pressure Motifs and Close‐Packing in Silicon Phosphorus Nitride Imide SiP2N4NH

Non‐metal nitrides such as BN, Si₃N₄, and P₃N₅ meet numerous demands on high‐performance materials, and their high‐pressure polymorphs exhibit outstanding mechanical properties. Herein, we present the silicon phosphorus nitride imide SiP₂N₄NH featuring sixfold coordinated Si. Using the multi‐anvil technique, SiP₂N₄NH was obtained by high‐pressure high‐temperature synthesis at 8 GPa and 1100 °C with in situ formed HCl acting as a mineralizer. Its structure was elucidated by a combination of single‐crystal X‐ray diffraction and solid‐state NMR measurements. Moreover, SiP₂N₄NH was characterized by energy‐dispersive X‐ray spectroscopy and (temperature‐dependent) powder X‐ray diffraction. The highly condensed Si/P/N framework features PN₄ tetrahedra as well as the rare motif of SiN₆ octahedra, and is discussed in the context of ambient‐pressure motifs competing with close‐packing of nitride anions, representing a missing link in the high‐pressure chemistry of non‐metal nitrides.     

Nitride Spinel: An Ultraincompressible High-Pressure Form of BeP2N4

Owing to its outstanding elastic properties, the nitride spinel γ-Si₃N₄ is of considered interest for materials scientists and chemists. DFT calculations suggest that Si₃N₄-analog beryllium phosphorus nitride BeP₂N₄ adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite-type BeP₂N₄ by single-crystal synchrotron X-ray diffraction and report the phase transition into the spinel-type phase at 47 GPa and 1800 K in a laser-heated diamond anvil cell. The structure of spinel-type BeP₂N₄ was refined from pressure-dependent in situ synchrotron powder X-ray diffraction measurements down to ambient pressure, which proves spinel-type BeP₂N₄ a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel-type BeP₂N₄ is an ultraincompressible material.     

Open‐Shell 3d Transition Metal Nitridophosphates MIIP8N14 (MII=Fe,Co, Ni) by High‐Pressure Metathesis

3d transition metal nitridophosphates M^IIP₈N₁₄ (M^II=Fe, Co, Ni) were prepared by high‐pressure metathesis indicating that this route might give a systematic access to a structurally rich family of M‐P‐N compounds. Their structures, which are stable in air up to at least 1273 K, were determined through powder X‐ray diffraction and consist of highly condensed tetra‐layers of PN₄ tetrahedra and MN₆ octahedra. Magnetic measurements revealed paramagnetic behavior of CoP₈N₁₄ and NiP₈N₁₄ down to low temperatures while, FeP₈N₁₄ exhibits an antiferromagnetic transition at T_N=3.5(1) K. Curie–Weiss fits of the paramagnetic regime indicate that the transition metal cations are in a oxidation state +II, which was corroborated by Mössbauer spectroscopy for FeP₈N₁₄. The ligand field exerted by the nitride ions in CoP₈N₁₄ and NiP₈N₁₄ was determined from UV/Vis/NIR data and is comparable to that of aqua‐ligands and oxophosphates.     

Li47B3P14N42—A Lithium Nitridoborophosphate with [P3N9]12−, [P4N10]10−, and the Unprecedented [B3P3N13]15− Ion

Li₄₇B₃P₁₄N₄₂, the first lithium nitridoborophosphate, is synthesized by two different routes using a Li₃N flux enabling a complete structure determination by single‐crystal X‐ray diffraction data. Li₄₇B₃P₁₄N₄₂ comprises three different complex anions: a cyclic [P₃N₉]¹²⁻, an adamantane‐like [P₄N₁₀]¹⁰⁻, and the novel anion [P₃B₃N₁₃]¹⁵⁻. [P₃B₃N₁₃]¹⁵⁻ is the first species with condensed B/N and P/N substructures. Rietveld refinement, ⁶Li, ⁷Li, ¹¹B, and ³¹P solid‐state NMR spectroscopy, FTIR spectroscopy, EDX measurements, and elemental analyses correspond well with the structure model from single‐crystal XRD. To confirm the mobility of Li⁺ ions, their possible migration pathways were evaluated and the temperature‐dependent conductivity was determined by impedance spectroscopy. With the Li₃N flux route we gained access to a new class of lithium nitridoborophosphates, which could have a great potential for unprecedented anion topologies with interesting properties.     

Beryllium‐Free β‐Rb2Al2B2O7 as a Possible Deep‐Ultraviolet Nonlinear Optical Material Replacement for KBe2BO3F2

A new beryllium‐free deep‐ultraviolet (DUV) nonlinear optical (NLO) material, β‐Rb₂Al₂B₂O₇ (β‐RABO), has been synthesized and characterized. The chiral nonpolar acentric material shows second‐harmonic generation (SHG) activity at both 1064 and 532 nm with efficiencies of 2×KH₂PO₄ and 0.4×β‐BaB₂O₄, respectively, and exhibits a short absorption edge below 200 nm. β‐Rb₂Al₂B₂O₇ has a three‐dimensional structure of corner‐shared Al(BO₃)₃O polyhedra. The discovery of β‐RABO shows that through careful synthesis and characterization, replacement of KBe₂BO₃F₂ (KBBF) by a Be‐free DUV NLO material is possible.