High-Pressure Synthesis of Sc5 P12 N23 O3 and Ti5 P12 N24 O2 by Activation of the Binary Nitrides ScN and TiN with NH4 F

ZnH2P4N8: Case Study on Topochemical Imidonitridophosphate High-Pressure Synthesis

Nitridophosphates are subject of current research, as they have a broad spectrum of properties and potential applications, such as ion conductors or luminescent materials. Yet, the subclass of imidonitridophosphates has been studied less extensively. The primary reason is that the controlled N-H functionalization of nitridophosphates is not straight forward, making targeted synthesis more challenging. Inspired by the high-pressure (HP) post-synthetic modification of nitridophosphates, we present the topochemical HP deprotonation of phosphorus nitride imides using the high-pressure polymorph β-PN(NH) as an example. Additional incorporation of Zn2+ results in the first quaternary transition metal imidonitridophosphate ZnH2P4N8. The crystal structure was elucidated by single-crystal X-ray diffraction (SCXRD), energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD) and solid-state magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). In addition, the presence of H as part of an imide group was confirmed by IR spectroscopy. The potential of this defunctionalization approach for controlling the N-H content is demonstrated by the preparation of partially deprotonated intermediates ZnxH4-2xP4N8 (x≈0.5, 0.85). This topochemical high-pressure reaction represents a promising way to prepare, control and manipulate new imide-based materials without altering their overall anionic framework.

Cr5.7Si2.3P8N24-A Chromium(+IV) Nitridosilicate Phosphate with Amphibole-Type Structure

The first nitridic analog of an amphibole mineral, the quaternary nitridosilicate phosphate Cr5.7Si2.3P8N24 was synthesized under high-pressure high-temperature conditions at 1400 °C and 12 GPa from the binary nitrides Cr2N, Si3N4 and P3N5, using NH4N3 and NH4F as additional nitrogen source and mineralizing agent, respectively. The crystal structure was elucidated by single-crystal X-ray diffraction with microfocused synchrotron radiation (C2/m, a=9.6002(19), b=17.107(3), c=4.8530(10) Å, β=109.65(3)°). The elemental composition was analyzed by energy dispersive X-ray spectroscopy. The structure consists of vertex-sharing PN4-tetrahedra forming zweier double chains and edge-sharing (Si,Cr)-centered octahedra forming separated ribbons. Atomic resolution scanning transmission electron microscopy shows ordered Si and Cr sites next to a disordered Si/Cr site. Optical spectroscopy indicates a band gap of 2.1 eV. Susceptibility measurements show paramagnetic behavior and support the oxidation state Cr+IV, which is confirmed by EPR. The comprehensive analysis expands the field of Cr-N chemistry and provides access to a nitride analog of one of the most prevalent silicate structures.

Discovery of Two Polymorphs of TiP 4 N 8 Synthesized from Binary Nitrides

TiP₄N₈ was obtained from the binary nitrides TiN and P₃N₅ upon addition of NH₄F as a mineralizer at 8 GPa and 1400 °C. An intricate interplay of disorder and polymorphism was elucidated by in situ temperature‐dependent single‐crystal X‐ray diffraction, STEM‐HAADF, and the investigation of annealed samples. This revealed two polymorphs, which consist of dense networks of PN₄ tetrahedra (degree of condensation κ=0.5) and either augmented triangular TiN₇ prisms or triangular TiN₆ prisms for α‐ and β‐TiP₄N₈, respectively. The structures of TiP₄N₈ exhibit body‐centered tetragonal (bct) framework topology. DFT calculations confirm the measured band gaps of α‐ and β‐TiP₄N₈ (1.6–1.8 eV) and predict the thermochemistry of the polymorphs in agreement with the experiments.

Nitridic Analogs of Micas AESi3 P4 N10 (NH)2 (AE=Mg, Mg0.94 Ca0.06 , Ca, Sr)

We present the first nitridic analogs of micas, namely AESi3 P4 N10 (NH)2 (AE=Mg, Mg0.94 Ca0.06 , Ca, Sr), which were synthesized under high-pressure high-temperature conditions at 1400 °C and 8 GPa from the refractory nitrides P3 N5 and Si3 N4 , the respective alkaline earth amides, implementing NH4 F as a mineralizer. The crystal structure was elucidated by single-crystal diffraction with microfocused synchrotron radiation, energy-dispersive X-ray spectroscopic (EDX) mapping with atomic resolution, powder X-ray diffraction, and solid-state NMR. The structures consist of typical tetrahedra-octahedra-tetrahedra (T-O-T) layers with P occupying T and Si occupying O layers, realizing the rare motif of sixfold coordinated silicon atoms in nitrides. The presence of H, as an imide group forming the SiN4 (NH)2 octahedra, is confirmed by SCXRD, MAS-NMR, and IR spectroscopy. Eu2+ -doped samples show tunable narrow-band emission from deep blue to cyan (451-492 nm).

High-Pressure Synthesis of Sc5 P12 N23 O3 and Ti5 P12 N24 O2 by Activation of the Binary Nitrides ScN and TiN with NH4 F

Multinary transition metal nitrides and oxonitrides are a versatile and intriguing class of compounds. However, they have been investigated far less than pure oxides. The compounds Sc5 P12 N23 O3 and Ti5 P12 N24 O2 have now been synthesized from the binary nitrides ScN and TiN, respectively, by following a high-pressure high-temperature approach at 8 GPa and 1400 °C. NH4 F acts as a mineralizing agent that supports product formation and crystallization. The starting materials ScN and TiN are seemingly an uncommon choice because of their chemical inertness but, nevertheless, react under these conditions. Sc5 P12 N23 O3 and Ti5 P12 N24 O2 crystallize isotypically with Ti5 B12 O26 , consisting of solely vertex-sharing P(O/N)4 tetrahedra forming two independent interpenetrating diamond-like nets that host TM(O/N)6 (TM=Sc, Ti) octahedra. Ti5 P12 N24 O2 is a mixed-valence compound and shows ordering of Ti3+ and Ti4+ ions.