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.

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.

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 β-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 β-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.

Tailoring the properties of 3d transition metal complexes with different N-cycloalkyl-substituted tetrazoles

N-Cycloalkyl-substituted tetrazoles were coordinated with different late 3d transition metal(ii) salts to give moderately sensitive energetic coordination compounds.

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.

New layered supertetrahedral compounds T2-MSiAs2, T3-MGaSiAs3 and polytypic T4-M 4Ga5SiAs9 (M = Sr, Eu)

The new supertetrahedral compounds MSiAs2, MGaSiAs3 and mC/tI-M 4Ga5SiAs9 (M = Sr, Eu) have been synthesized by solid-state reactions at high temperatures. The structures were determined by single crystal or powder X-ray diffraction. MSiAs2 and MGaSiAs3 crystallize in the monoclinic TlGaSe2- and RbCuSnS3-type structures, respectively (space group C2/c). These are topologically hierarchical variants of the tetragonal HgI2-type structure with stacked layers of T2 or T3 supertetrahedra. The T4 compounds M 4Ga5SiAs9 are dimorphic and form new structure types in the space groups C2/c and I41/amd, respectively. The latter exhibits coinciding layer stacking as known from tetragonal HgI2. The T4 compounds close the gap between the longer known T2 types and the recently reported compounds with T5 and T6 supertetrahedra. Measurements of the optical band gap, electrical resistivity and Hall Effect support the semiconducting nature of M 4Ga5SiAs9. Magnetization measurements confirm Eu2+ in Eu4Ga5SiAs9 and indicate ferromagnetism below T = 2 K.

High-pressure synthesis and crystal structure of SrGa4As4

Strontium tetra-gallate(II,III) tetra-arsenide, SrGa₄As₄, was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 8 GPa and 1573 K. The com-pound crystallizes in a new structure type (P3₂21, Z = 3) as a three-dimensional (3D) framework of corner-sharing SrAs₈ quadratic anti-prisms with strontium situated on a twofold rotation axis (Wyckoff position 3b). This arrangement is surrounded by a 3D framework which can be described as alternately stacked layers of either condensed Ga^IIIAs₄ tetra-hedra or honeycomb-like layers built up from distorted ethane-like Ga^II ₂As₆ units com-prising Ga-Ga bonds.

Direct Spectroscopic Detection of Key Intermediates and the Turnover Process in Catalytic H2 Formation by a Biomimetic Diiron Catalyst

[FeFe(Cl₂ -bdt)(CO)₆ ] (1; Cl₂ -bdt=3,6-dichlorobenzene-1,2-dithiolate), inspired by the active site of FeFe-hydrogenase, shows a chemically reversible 2 e^- reduction at -1.20 V versus the ferrocene/ferrocenium couple. The rigid and aromatic bdt bridging ligand lowers the reduction potential and stabilizes the reduced forms, compared with analogous complexes with aliphatic dithiolates; thus allowing details of the catalytic process to be characterized. Herein, time-resolved IR spectroscopy is used to provide kinetic and structural information on key catalytic intermediates. This includes the doubly reduced, protonated complex 1H^- , which has not been previously identified experimentally. In addition, the first direct spectroscopic observation of the turnover process for a molecular H₂ evolving catalyst is reported, allowing for straightforward determination of the turnover frequency.

Flux synthesis, crystal structures, and physical properties of new lanthanum vanadium oxyselenides

The new lanthanum vanadium oxyselenides LaVSe₂O, La₅V₃Se₆O₇, La₅V₃Se₇O₅, La₇VSe₅O₇, and La₁₃V₇Se₁₆O₁₅ were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined using single-crystal and powder X-ray diffraction experiments. LaVSe₂O and La₅V₃Se₆O₇ adopt known structure types, whereas La₅V₃Se₇O₅, La₇VSe₅O₇, and La₁₃V₇Se₁₆O₁₅ crystallize in hitherto unknown structure types. The main building blocks of these compounds are chains of edge-sharing VSe₆, VSe₅O, and/or VSe₄O₂ octahedra, linked together by edge-sharing OLa₄ and/or OLa₃V tetrahedra forming fluorite-like ribbons. LaVSe₂O, La₅V₃Se₇O₅, and La₇VSe₅O₇ contain only V(iii) ions, whereby La₅V₃Se₆O₇ and La₁₃V₇Se₁₆O₁₅ contain mixtures of either V(iii)/V(iv) or V(iii)/V(v) cations. Magnetic measurements indicate Curie-Weiss paramagnetism and magnetic ordering of the vanadium moments at low temperatures. More precisely, we observe antiferromagnetism for La₅V₃Se₆O₇, metamagnetism for La₅V₃Se₇O₅, ferromagnetism for La₇VSe₅O₇ and a complex magnetic structure for La₁₃V₇Se₁₆O₁₅.

Flux Synthesis, Crystal Structures, and Magnetic Ordering of the Rare-Earth Chromium(II) Oxyselenides RE2CrSe2O2 (RE = La-Nd)

The rare-earth chromium(II) oxyselenides RE₂CrSe₂O₂ (RE = La-Nd) were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined by single-crystal and powder X-ray diffraction (Pb₂HgCl₂O₂-type, C2/m, Z = 2). The magnetic structure of La₂CrSe₂O₂ was solved and refined from neutron powder diffraction data. Main building blocks are chains of edge-sharing CrSe₄O₂ octahedra linked together by two edge-sharing ORE₃Cr tetrahedra forming infinite ribbons. The Jahn-Teller instability of divalent Cr²⁺ (d⁴) leads to structural phase transitions at 200 and 130 K in La₂CrSe₂O₂ and Ce₂CrSe₂O₂, respectively. RE₂CrSe₂O₂ are Curie-Weiss paramagnetic above T_N ≈ 14-17 K. Neutron powder diffraction reveals anti-ferromagnetic ordering of the Cr²⁺ moments in La₂CrSe₂O₂ below T_N = 12.7(3) K with an average ordered moment of 3.40(4) μ_B/Cr²⁺ at 4 K, which was confirmed by muon spin rotation experiments.