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We report on the synthesis, crystal, and electronic structure, as well as the magnetic, and electric properties of the phosphorus-containing tantalum nitride P1-xTa8+xN13 (x = 0.1-0.15). A high-pressure high-temperature reaction (8 GPa, 1400 °C) of Ta3N5 and P3N5 with NH4F as a mineralizing agent yields the compound in the form of black, rod-shaped crystals. Single-crystal X-ray structure elucidation (space group C2/m (no. 12), a = 16.202(3), b = 2.9155(4), c = 11.089(2) Å, β = 126.698(7)°, Z = 2) shows a network of face- and edge-sharing Ta-centered polyhedra that contains small vacant channels and  PN6 octahedra strands. Atomic resolution transmission electron microscopy reveals an unusual P/Ta disorder. Mixed-valent tantalum atoms exhibit interatomic distances similar to those in metallic tantalum, however, the electrical resistivity is quite high in the order of 10‑1 Ω cm. The density of states and the electron localization function indicate localized electrons in both covalent and ionic bonds between P/Ta and N atoms, combined with less localized electrons that do not contribute to interatomic bonds., (© 2024 Wiley‐VCH GmbH.)

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 Eu 2+ , making them appealing for industrial applications. Here, we present the first nitridomagnesophosphate solid solution series Ba 3-x Sr x [Mg 2 P 10 N 20 ] : Eu 2+ (x=0-3), synthesized by a high-pressure high-temperature approach using the multianvil technique (3 GPa, 1400 °C). Starting from the binary nitrides P 3 N 5 and Mg 3 N 2 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. Eu 2+ -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 Ba 2 Eu[Mg 2 P 10 N 20 ] with additional atomic resolution energy-dispersive X-ray spectroscopy (EDX) mapping., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A series of isostructural imidonitridophosphates AE 2 AlP 8 N 15 (NH) (AE=Ca, Sr, Ba) was synthesized at high-pressure/high-temperature conditions (1400 °C and 5-9 GPa) from alkaline-earth metal nitrides or azides Ca 3 N 2 /Sr(N 3 ) 2 /Ba(N 3 ) 2 and the binary nitrides AlN and P 3 N 5 . NH 4 F served as a hydrogen source and mineralizing agent. The crystal structures were determined by single-crystal X-ray diffraction and feature a three-dimensional network of vertex-sharing PN 4 -tetrahedra forming diverse-sized rings that are occupied by aluminum and alkaline earth ions. These structures represent another example of nitridophosphate-based networks that simultaneously incorporate AlN 6 -octahedra and alkaline-earth-centered polyhedra, with aluminum not participating in the tetrahedra network. They differ from previously reported ones by incorporating non-condensed octahedra instead of strongly condensed octahedra units and contribute to the diversity of multicationic nitridophosphate network structures. The results are supported by atomic resolution EDX mapping, solid-state NMR and FTIR measurements. Eu 2+ -doped samples show strong luminescence with narrow emissions in the range of green to blue under UV excitation, marking another instance of Eu 2+ -luminescence within imidonitridophosphates., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The first nitridic analog of an amphibole mineral, the quaternary nitridosilicate phosphate Cr 5.7 Si 2.3 P 8 N 24 was synthesized under high-pressure high-temperature conditions at 1400 °C and 12 GPa from the binary nitrides Cr 2 N, Si 3 N 4 and P 3 N 5 , using NH 4 N 3 and NH 4 F 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 PN 4 -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., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Tetrahedra-based nitridophosphates show a rich structural chemistry, which can be further extended by incorporating cations in higher coordinated positions, for example, in octahedral voids or by substituting the nitrogen atoms in the network with other anions. Following this approach, SrAl 5 P 4 N 10 O 2 F 3 was synthesized at high-temperature and high-pressure conditions using a multianvil press (1400 °C, 5 GPa) starting from Sr(N 3 ) 2 , c-PON, P 3 N 5 , AlN, and NH 4 F. SrAl 5 P 4 N 10 O 2 F 3 crystallizes in space group I 4 ‾ m 2 ${I\bar 4m2}$ with a=11.1685(2) and c=7.84850(10) Å. Atomic-resolution EDX mapping with scanning transmission electron microscopy (STEM) indicates atom assignments, which are further corroborated by bond-valence sum (BVS) calculations. Ten Al 3+ -centered octahedra form a highly condensed tetra-face-capped octahedra-based unit that is a novel structure motif in network compounds. A network of vertex-sharing PN 4 tetrahedra and chains of face-sharing Sr 2+ -centered cuboctahedra complement the structure. Eu 2+ -doped SrAl 5 P 4 N 10 O 2 F 3 shows blue emission (λ em= 469 nm, fwhm=98 nm; 4504 cm -1 ) when irradiated with UV light., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)