Zur Chemie und Strukturchemie von Phosphiden und Polyphosphiden. 581) Tetrabariumtriphosphid,Ba4P3: Darstellung und Kristallstruktur

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 58. Tetrabariumtriphosphide, Ba₄P₃: Preparation and Crystal Structure Ba₄P₃ is obtained from the elements in the molar ratio 4:3 or by reaction of Ba₃P₂ and Ba₅P₄ in the molar ratio 1:1 (steel ampoules with inner corundum crucibles; 1 490 K). The greyish black, easily hydrolysing compound crystallizes in a new structure type oP56. The structure shows two crystallographically independent dumbbells P₂^4? (d(P? P) = 225 and 232 pm) and isolated ions P^3? corresponding to (Ba²⁺)₈(P₂^4?)₄(P^3?)₄. The partial structure of the Ba atoms forms a complex network of trigonal prisms with tetrahedral and square pyramidal holes, as well as polyhedra with 14 faces (CN 10) which are icosahedron derivatives. The P^3? anions center trigonal prisms and the 14 face polyhedron. The P-atoms of the P₂^4? dumbbells center neighboring trigonal prisms with common square faces. (Pbam (no. 55); a = 1 325.4(2) pm, b = 1 256.2(2) pm, c = 1 127.3 pm; Z = 8).     

Zur Chemie und Strukturchemie der Phosphide und Polyphosphide. 34 [1] Dampfdruckuntersuchungen am System Europium–Phosphor

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 34. Vapor Pressure Measurements in the Europium-Phosphorus System The vapor pressure of the europium phosphides EuP₇, α-EuP₃, ß-EuP₃, EuP₂ and Eu₃P₄ were measured using the Knudsen-Effusion technique. These compounds were vaporized incongruently according to the general reaction a EuP_m, (s) = a EuP_n, (s) + P₄, (g) where a (m—n) = 4. The following enthalpies and entropies of reaction were calculated (δH)kJ · mol^?1/δS (J · K^?1 mol^?1)/ T(K). [δH/δS/T]: EuP₇ → ß-EuP₃ [191/215/698]; α-EuP₃ → EuP₂ [212/162/847]; ß-EuP₃ → EuP₂ [261/212/847]; EuP₂ → Eu₃P₄ [209/144/868]; Eu₃P₄ → EuP [240/131/1110]. The temperature and pressure ranges over which these phosphides exist were determined from the above values. Standard enthalpies of formation relative to EuP(s) were calculated by combining different reaction enthalpies. The results demonstrate the relatively high stability of ß-EuP₃, EuP₇ and the instability of EuP₂.     

Zur Chemie und Strukturchemie der Phosphide und Polyphosphide. 26. Dibariumheptaphosphidchlorid Ba2P7Cl,eine Verbindung mit dem polycyclischen Anion P

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 26. Dibariumheptaphosphidechloride Ba₂P₇Cl, a Compound with the Polycyclic Anion P Ba₂P₇Cl is formed by the synthesis of Ba₃P₁₄ from the elements in a melt of BaCl₂ (dehydrated) at 1170 K. The compound forms light rubyred platelets which decompose in protic systems immediately to phosphanes. Ba₂P₇Cl crystallizes in the space group P2₁/m with Z = 2 formular units (a = 1172.6(2) pm; b = 682.9(1) pm; c = 633.7(1) pm; β = 95.27(2)°). The structure (964 reflexions hkl, R = 0.035) is related to the NaCl type, in which the half of the anionic positions is occupied by the gravi-centers of the polycyclic anions P. The bond lengths d(P? P) show the typical topological dependence for the anionic heptaphosphanortricyclene system: (d : 226.4 pm in the three-membered ring; 214.5 pm ring to bridge; 217.2 pm bridge to bridge head). The Ba atoms are surrounded by 9 and 10 non metallic atoms, respectively. Cl^? is coordinated tetrahedrally by Ba.     

Zur Chemie und Strukturchemie von Phosphiden und Polyphosphiden. 42. Trilithiumheptaphosphid Li3P7: Darstellung,Struktur und Eigenschaften

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 42. Trilithiumheptaphosphide Li₃P₇: Preparation, Structure, and Properties Trilithium heptaphosphide, Li₃P₇, has been prepared by reaction of the elements at 870 K in Nb and Ta ampoules, respectively. The bright yellow (solventfree) substance crystallizes in a new structure type (P2₁2₁2₁; a = 974.2(1) pm; b = 1053,5(1) pm; c = 759,6(1) pm; Z = 4). The structure is closely related to the plastically crystalline Rb₃P₇ type of structure (Li₃Bi variant). The heptaphosphanortricyclene anions P₇^3? are surrounded by 12 Li cations and connected one to each other in a complex manner. The anion exhibits a differentation of distances and angles typical for ionic nortricyclenes X₇^3? (P? P distances: d?(basis) = 224.9 pm; d?(basis-bridge) = 214.7 pm; d?(bridge-bridgehead) = 217.6 pm). The distances Li to P are in the range of 250 ≤ d(Li? (2b)P^?) ≤ 270 pm. The P? P and Li? P bond distances are equivalent to meaningful Pauling bond orders PBO. On heating in closed ampoules, Li₃P₇ shows an endothermic effect at 900 K, corresponding to a first order phase transition into a HT phase of unknown nature up to now. On thermal decomposition no congruent dissociative sublimation occurs in contrast to the other heptaphosphides M₃P₇, but LiP and Li₃P are formed, the latter evaporates congruently dissociative, Solutions of Li₃P₇ in en show valence fluctuation of the P₇^3? anions already at room temperature (δ ³¹P-NMR = ? 122.1). Further reactions of Li₃P₇ are reported as well as the structural differences between Li₃P₇ and the solvates Li₃P_7solv3 are discussed.     

Sr13□NbAs11 and Eu13□NbAs11 – Defect Variants of the Ca14AlSb11 Structure with asymmetric [As3]7− anions

The novel compounds Sr₁₃NbAs₁₁ and Eu₁₃NbAs₁₁ have been synthesized from SrAs, Eu₅As₄, Sr, Nb and As in niobium ampoules at 1173–1273 K. The tetragonal tI 200 phases are defect variants of the Ca₁₄AlSb₁₁ structure (space group I4₁/acd (no. 142); Sr₁₃□NbAs₁₁: a = 1649.8(2) and c = 2214.1(3); Eu₁₃□NbAs₁₁: a = 1632.9(8) and c = 2197.3(8) pm; Z = 8). The structures are built from the cations Sr²⁺, and Eu²⁺, respectively, and from the anions [NbAs₄]^7?, As^3?, and the linear polyanion [As₃]^7?. This polyanion (isosteric to I₃^?) is asymmetric with d(As? As) = 273.0 and 346.0 pm (Sr) and 274.7 and 335.6 pm (Eu), respectively. The bond lengths in the tetrahedral anions are d(Nb? As) = 250.8 and 251.1 pm. The complete structural arrangement is related to that of Cu₂O by forming two interpenetrating networks. The oxygen atoms are substituted by niobium centered As₄ tetrahedra, and the Cu atoms are substituted by As₆ octahedra (centered by Sr, Eu). The central As atoms of the polyanions connect the nets. Both As networks are enveloped by the remaining cations forming cubes, tetragonal antiprisms and capped trigonal prisms.     

Zur Chemie und Strukturchemie von Phosphiden und Polyphosphiden. 36. Tetrakaliumhexaphosphid: Darstellung,Struktur und Eigenschaften von α-K4P6 und β-K4P6

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 36. Tetrapotassiumhexaphosphide: Preparation, Structure, and Properties of α-K₄P₆ and β-K₄P₆ Tetrapotassiumhexaphosphide has been prepared quantitatively by reaction of the elements at 870 K in sealed Nb and Ta ampoules, respectively. Two crystalline modifications are formed: α-K₄P₆ is stable below 850 K, β-K₄P₆ is stable above this temperature. Both compounds are black semiconductors (E_G(α) = 0.55 eV) with metallic lustre. The orthorhombic structures are defect variants of the hexagonal AlB₂ type structures (K₄P₆□₂) and of a different stacking sequence of this type. Characteristic building units are planar isometric P₆ rings, formed by a specific ordering of defects in the partial structure of the major component. The short P? P distances (215.5 pm and 215.0 pm, respectively) are about 30 pm shorter than the distances compared with a single bond (221 pm). They represent one double bond which is delocalized about six bonds or an aromatic 2π-system. The thermal decomposition in tantalum crucibles, the reaction with quartz walls as well as the reaction with benzophenone in monoglyme yields quantitatively K₃P₇. The reaction with RCl ? Me₃SnCl in monoglyme at 223 K results in the formation of P₇R₃ with high yield (75%). Very probably the valence fluctuating hexaphosphene(4) system is formed at 195 K in the primary reaction step (³¹P-NMR, singulett at 473 ppm downfield).     

Zur Chemie und Strukturchemie der Phosphide und Polyphosphide. 27. Bariumdecaphosphid BaP10

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 27. Bariumdecaphosphide BaP₁₀ Black, reflective crystals of BaP₁₀ are formed by the reaction of BaP₃ with red phosphorus at 1 050 K. The absorption edge at 765 nm corresponds to a band gap of 1.62 eV. The compound is resistant to both acids and bases. The thermal decomposition to Ba₃P₁₄ and then to BaP₃ and other lower phosphides occurs at 725 K. BaP₁₀ crystallizes in the orthorhombic space group Cmc2₁ (No. 36) with 4 formula units (a = 645.2(1), b = 1 258.9(2), c = 1 192.7(2) pm). The structure (632 reflections hkl; R = 0.019) contains the 2-dimensional infinite polyanion [P₁₀^2?], which also characterizes the structure of TlP₅. It originates through the connection of 1-dimensional pentagonal phosphorus tubes, which corresponds to those in the structure of Hittorf's phosphorus and KP₁₅ (bond lengths P? P = 215.0–224.5 pm). Ba is coordinated by 12 P-atoms with distances of 332.7 pm to 374.3 pm.     

Zur Chemie und Strukturchemie von Phosphiden und Polyphosphiden. 44. Tricäsiumheptaphosphid Cs3P7: Darstellung,Struktur und Eigenschaften

Chemistry and Structural Chemistry of Phosphides and Ployphosphides. 44. Tricesium Heptaphosphide Cs₃P₇: Preparation, Structure, and Properties Tricesium heptaphosphide is prepared from the elements by a quantitative reaction at 1200 K in Nb ampoules. Slow cooling yield the bright yellow α-Cs₃P₇, quenching the yellow orange coloured β-Cs₃P₇. The crystalline α-Cs₃P₇ transforms at 552 K in a first order phase transition to the plastically crystalline β-Cs₃P₇. Both modifications are sensitive against moisture and oxygen and are completely soluble in ethylendiamine yielding a pale yellow solution. At room temperature the ³¹P nmr spectra of such solutions show only one singulett, which corresponds to the valence tautomerism of the P₇^3? anion. α-Cs₃P₇ crystallizes in a new structure type (P4₁, a = 904.6(1) pm; c = 1671.4(4) pm; Z = 4). The structure is formed by heptaphospha-nortricyclene anions P₇^3? and Cs⁺ cations. The cs atoms connect the anions forming a three-dimensional arrangement (d?(Cs? P) = 374 pm), not allowing the fragmentation into discrete Cs₃P₇ units. The P? P distances differ by their function in the nortricyclene anion. Each P₇ group is surrounded by 12 Cs atms. β-Cs₃P₇ crystallizes in the Li₃Bi type of structure (Fm3 M; a(573 K) = 1130.5(1)pm; Z = 4). The P atoms of the P₇^3? anions surround the Bi positions with an orienational disorder. The orientation has been investigated with a mixed crystal Ca₃(P₇)_2/3(P₁₁)_1/2 (Fm3 m; a (298 K) = 1149.5(9) pm; Z = 4).     

Zur Chemie und Strukturchemie der Phosphide und Polyphosphide. 20. Darstellung,Struktur und Eigenschaften der Alkalimetallmonophosphide NaP und KP

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 20. Preparation, Structure, and Properties of the Alkali Metal Monophosphides NaP and KP The monophosphides NaP and KP were prepared by reaction of the elements in sealed glass ampoules at 725 K and 765 K, respectively. NaP yields as black reflecting needles, whereas KP is formed as microcrystalline substance with colour of coke. The compounds react very rapidly with aqueous reagents forming solid polymeric yellow phosphanes (PH)_x and partially gaseous products. NaP and KP crystallize in the novel orthorhombic NaP type (P 2₁2₁2₁; a = 603,8 pm; b = 564.3 pm; c = 1 014.2 pm and a = 650.0 pm; b = 601.6 pm; c = 1 128.8 pm; Z = 8, respectively) characterized by onedimensional infinite ¹∞(P^?) helices of covalent twofold bonded P-atoms with mean bond length P? P = 223.9 pm. The compounds can be described as Zintl-phases with M⁺ and P^? with respect to the structure. The range of existence of the NaP type and the LiAs type structure can be separated by the radii ratios. The volume increment for P^? is V(P^?) = 18.0 cm³mol^?1. For the bond energy E(P? P) in the monophosphides a value of 248 kJ · mol^?1 is calculated. The structures are discussed in detail together with related compounds.     

Die neuen Schichtsilicate Ba3Si6O9N4 und Eu3Si6O9N4

The New Layer‐Silicates Ba₃Si₆O₉N₄ and Eu₃Si₆O₉N₄ The new oxonitridosilicate Ba₃Si₆O₉N₄ has been synthesized in a radiofrequency furnace starting from BaCO₃, amorphous SiO₂ and Si₃N₄. The reaction temperature was at about 1370 °C. The structure of the colorless compound has been determined by single‐crystal X‐ray diffraction analysis (Ba₃Si₆O₉N₄, space group P3 (no. 143), a = 724.9(1) pm, c = 678.4(2) pm, V = 308.69(9)· 10⁶ pm³, Z = 1, R1 = 0.0309, 1312 independent reflections, 68 refined parameters). The compound is built up of corner sharing SiO₂N₂ tetrahedra forming corrugated layers between which the Ba²⁺ ions are located. Substitution of barium by europium leads to the isotypic compound Eu₃Si₆O₉N₄. Because no single‐crystals could be obtained, a Rietveld refinement of the powder diffractogram was conducted for the structure refinement (Eu₃Si₆O₉N₄, space group P3 (no. 143), a = 711.49(1) pm, c = 656.64(2) pm, V = 287.866(8) ·10⁶ pm³, R_p = 0.0379, R_F² = 0.0638). The ²⁹Si MAS‐NMR spectrum of Ba₃Si₆O₉N₄ shows two resonances at ?64.1 and ?66.0 ppm confirming two different crystallographic Si sites.     

Neue Hexachalcogeno‐Hypodiphosphate der Erdalkalimetalle und des Europiums

New Hexachalcogeno‐Hypodiphosphates of Alkaline‐Earth Metals and Europium Six hexathio‐ and hexaseleno‐hypodiphosphates respectively with the formula M₂P₂X₆ (M = Ca, Sr, Eu, Ba; X = S, Se) were prepared by heating the elements at 750 °C (60 h) and their crystal structures were determined by single crystal X‐ray methods. Eu₂P₂S₆ (a = 9.396(2), b = 7.531(2), c = 6.593(2) Å, β = 91.48(2) °), Ba₂P₂S₆ (a = 9.966(1), b = 7.580(2), c = 6.737(2) Å, β = 91.17(3) °), Ca₂P₂Se₆ (a = 9.664(2), b = 7.519(2), c = 6.859(1) Å, β = 92.02(3) °), Sr₂P₂Se₆ (a = 9.844(2), b = 7.788(2), c = 6.963(1) Å, β = 91.50(3) °), Eu₂P₂Se₆ (a = 9.779(2), b = 7.793(2), c = 6.957(1) Å, β = 91.29(3) °), and Ba₂P₂Se₆ (a = 10.355(2), b = 7.862(2), c = 7.046(1) Å, β = 90.83(3) °) are isotypic and crystallize in the high temperature form of Sn₂P₂S₆ (P2₁/n; Z = 2). The discrete ethanlike (P₂X₆)^4— anions in staggered conformation are linked via X—M—X bonds to a three‐dimensional structure and in the course of this Ca²⁺, Sr²⁺, and Eu²⁺ are coordinated by 8 and Ba²⁺ by 8+1 S and Se atoms respectively. Susceptibility measurements of Eu₂P₂S₆ from 2 K to room temperature show Curie‐Weiss behavior with an experimental magnetic moment of 7.43(2) μ_B/Eu. No magnetic ordering was observed down to 2 K. A ¹⁵¹Eu Mössbauer spectrum at 77 K shows only one signal at an isomer shift of δ = —12.6(1) mm/s. The europium atoms in Eu₂P₂S₆ are therefore in a stable divalent oxidation state.     

Synthese und Kristallstruktur des ersten Oxonitridoborates — Sr3[B3O3N3]

Synthesis and Crystal Structure of the First Oxonitridoborate — Sr₃[B₃O₃N₃] The cyclotri(oxonitridoborate) Sr₃[B₃O₃N₃] was synthesized at 1450 °C as coarsely crystalline colourless crystals by the reaction of SrCO₃ with poly(boron amide imide) using a radiofrequency furnace. The structure was solved by single‐crystal X‐ray diffractometry (Sr₃[B₃O₃N₃], Z = 4, P2₁/n, a = 663.16(2), b = 786.06(2), c = 1175.90(3) pm, η = 92.393(1)°, R1= 0.0441, wR2 = 0.1075, 1081 independent reflections, 110 refined parameters). Besides Sr²⁺ there are hitherto unknown cyclic [B₃O₃N₃]^6— ions (B—N 143.7(10) — 149.1(9) pm, B—O 140.5(8) — 141.4(8) pm).     

Ba2(CN2)(CN)2 und Sr2(CN2)(CN)2 – die ersten gemischten Cyanamid-cyanide

Ba₂(CN₂)(CN)₂ and Sr₂(CN₂)(CN)₂ – the First mixed Cyanamide Cyanides The mixed cyanamide-cyanides M₂(CN₂)(CN)₂ (M = Ba, Sr) were synthesized by the reaction of Ba₂N and SrCO₃, respectively, with HCN at 630°C. The crystal structure of Ba₂(CN₂)(CN)₂ was determined from single-crystal X-ray investigations at room temperature and ?100°C; the isostructural Sr₂(CN₂)(CN)₂ was refined using powder methods (P6₃/mmc; Ba₂(CN₂)(CN)₂: a = 1 066.52(5) pm, c=696.82(3) pm; Sr₂(CN₂)(CN)₂: a = 1 035.91(1) pm, c = 664.23(1) pm; Z = 4). The crystal structure is a partially filled defect variant of the anti-NiAs structure type with a distorted hexagonal close packed arrangement of M²⁺-ions. All CN₂^2? and one quarter of the CN^? ions occupy 3/4 of the octahedrally coordinated interstices, the remaining cyanide anions are located at 3/8 of the tetrahedral sites. In the crystal structure the CN^? are coordinated to the cations both end-on and side-on. All anions can be distinguished by vibrational spectroscopy.     

Überblick über die Phosphide des Strontiums

The method of the reaction in a stainless steel cube which was used for the first time in the preparation of barium phosphides is also applicable to phosphide-producing mixtures of strontium and phosphorus. In connection with high temperature experiments it served to obtain a survey of the binary system strontium—phosphorus. This binary system is largely analogous to the binary system barium—phosphorus. The compounds found were: “Sr₂P”, Sr₃P₂, Sr₄P₃? Sr_1,1P, SrP, Sr₄P₅ and SrP². The strontium-rich phosphides have melting or decomposing temperatures which are higher than those of the analogous barium phosphides. The powders of Sr₃P₂, Sr₄P₃ and SrP are brown to blackviolet. Sr₃P₂ cristallizes isostructurally with Ba₃P₂. Some properties indicate that the bonding is more ionic than in Ba₃P₂. The structural relationship of the alkaline earth pnietides with the lanthanide chalogenides is discussed. Sr₃P₂ and Ba₃P₂ complete the inverse isostructures of these compounds.     

Struktur‐ und magnetochemische Untersuchungen an Ba5Mn3F19 und verwandten Verbindungen AII5MIII3F19

Structural and Magnetochemical Studies of Ba₅Mn₃F₁₉ and Related Compounds A^II₅M^III₃F₁₉ Single crystal structure determinations by X‐ray methods were performed at the following compounds, crystallizing tetragonally body‐centred (Z = 4): Sr₅V₃F₁₉ (a = 1423.4(2), c = 728.9(1) pm), Sr₅Cr₃F₁₉ (a = 1423.5(2), c = 728.1(1) pm), Ba₅Mn₃F₁₉ (a = 1468.9(1), c = 770.3(1) pm, Ba₅Fe₃F₁₉ (a = 1483.5(1), c = 766.7(1) pm), and Ba₅Ga₃F₁₉ (a = 1466.0(2), c = 760.1(2) pm). Only Ba₅Mn₃F₁₉ was refined in space group I4cm (mean distances for elongated octahedra Mn1–F: 185/207 pm equatorial/axial; for compressed octahedra Mn2–F: 199/182 pm), the remaining compounds in space group I4/m. In all cases the octahedral ligand spheres of the M1 atoms showed disorder, the [M1F₆] octahedra being connected into chains in one part of the compounds and into dimers in the other. The magnetic properties of the V, Cr and Mn compounds named above and of Pb₅Mn₃F₁₉ and Sr₅Fe₃F₁₉ as well were studied; the results are discussed in context with the in part problematic structures.     

Improving LED Efficiency with the New Polymorph β-Ca1−xSrxAlSiN3:Eu2+

Innovative materials for phosphor-converted white light-emitting diodes (pc-LEDs) are much sought after due to the huge potential of the LED technology to reduce energy consumption worldwide. One of the main levers for further improvements are the conversion phosphors. The system Ca_1−xSr_xAlSiN₃:Eu²⁺ currently provides one of the most important red-emitting phosphors for pc-LEDs. We report the discovery of the new polymorph β-Ca_1−xSr_xAlSiN₃:Eu²⁺ which allows for significant improvements to LED efficacies. It crystallizes in the orthorhombic space group Pbcn with lattice parameters a=982.43(10) pm, b=575.2(1) pm and c=516.12(5) pm. Compared to α-Ca_1−xSr_xAlSiN₃:Eu²⁺, its emission shows a significantly reduced spectral full-width at half maximum (FWHM). With that, we demonstrated 3 % efficacy increase for white light-emitting pc-LEDs. The new polymorph can easily be industrialised, because the synthesis works on the same equipment as α-Ca_1−xSr_xAlSiN₃:Eu²⁺.     

Synthesis,Persistent Luminescence,and Thermoluminescence Properties of Yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce,Nd, Dy,Ho, Er,Tm, Yb) and Orange‐Red Sr3−xBaxSiO5:Eu2+, Dy3+ Phosphor

Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu²⁺ in Sr₃SiO₅ was significantly modified. The yellow persistent emission intensity of Eu²⁺ was greatly enhanced by a factor of 4.5 in Sr₃SiO₅:Eu²⁺,Nd³⁺ compared with the previously reported Sr₃SiO₅:Eu²⁺, Dy³⁺. Furthermore, Sr ions were replaced with equivalent Ba to give Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu²⁺ is significantly improved by a factor of 2.7 in Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ (x=0.2) compared with Sr₃SiO₅:Eu²⁺,Dy³⁺. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu²⁺ in Sr_3?xBa_xSiO₅:Eu²⁺,RE³⁺ (RE=rare earth) is also proposed and discussed.     

Neue Tetrapnictidotitanate(IV): Na3M3[TiX4] mit M  Na/Sr,Na/Eu und X  P,As

New Tetrapnictidotitanates(IV): Na₃M₃[TiX₄] with M ? Na/Sr, Na/Eu and X ? P, As The four novel tetrapnictidotitanates(IV) Na₄Sr₂TiP₄, Na₄Sr₂TiAs₄, Na_4.3Eu_1.7TiP₄ and Na_4.3Eu_1.7TiAs₄ were prepared from the binary pnictides NaX, M₃X, M′X (X ? P, As and M′ ? Sr, Eu) and elementary titanium in tantalum ampoules. The air and moisture sensitive transition metal compounds form dark red hexagonal crystals. They are semiconductors with E_g = 1.8eV (Sr) and E_g = 1.3eV (Eu), respectively. The compounds are isotypic with Na₆ZnO₄ (space group P6₃mc (no. 186); hP22; Z = 2; Na₄Sr₂TiP₄; a = 936.8(1) pm, c = 740.5(1) pm; Na₄Sr₂TiAs₄: a = 958.2(1) pm, c = 757.1(1) pm; Na_4.3Eu_1.7TiP₄: a = 929.9(2) pm, c = 732.0(2) pm; Na_4.3Eu_1.7TiAs₄: a = 953.9(1) pm, c = 749.5(1) pm). Main structural units are polar oriented [TiP₄]^8? and [TiAs₄]^8? tetrahedral anions with d (Ti? P) = 240.2(3) pm and d (Ti? As) = 248.6(3) pm.     

Darstellung und Kristallstruktur der Pnictidoxide Na2Ti2As2O und Na2Ti2Sb2O

Preparation and Crystal Structure of the Pnictide Oxides Na₂Ti₂As₂O and Na₂Ti₂Sb₂O Na₂Ti₂As₂O and Na₂Ti₂Sb₂O were synthesized in form of very easily hydrolysed metallic-grey powders by reaction of Na₂O and TiAs resp. TiSb in sealed tantalum tubes under argon. The tetrahedral bodycentered crystallizing compounds from a modified anti-K₂NiF₄ structure type [1] (also called Eu₄As₂O-type [2,3]), space group I4/mmm (no. 139), with the lattice constants for Na₂Ti₂As₂O: a = 407.0(2) pm, c = 1528.8(4) pm and for Na₂Ti₂Sb₂O: a = 414.4(0) pm, c = 1656.1(1) pm. Magnetic measurements of powder samples of Na₂Ti₂Sb₂O show antiferromagnetic interaction within the Ti—O-layers. Superconductivity was not found by ac-shielding method down to 4 K.     

Tetrapnictidotitanate(IV) M4TiX4 (M = Sr,Ba; X = P,As), hierarchische Derivate der KGe-Struktur K4□Ge4

Tetrapnictidotitanates(IV) M₄TiX₄ (M = Sr, Ba; X = P, As), hierarchical Derivatives of the KGe Structure K₄□Ge₄ The four new tetrapnictidotitanates(IV) Sr₄TiP₄, Sr₄TiAs₄, Ba₄TiP₄ and Ba₄TiAs₄ are synthesized from the binary pnictides MX (M = Sr, Ba and X = P, As) and elementary titanium in tantalum ampoules. The compounds are isotypic and isoelectronic with Ba₄SiAs₄ (space group P4 3n (no. 218); cP72; Z = 8; Sr₄TiP₄: a = 1259.0(1) pm; Sr₄TiAs₄: a = 1288.3(4) pm; Ba₄TiP₄: a = 1316.6(2) pm; Ba₄TiAs₄: a = 1346.9(2) pm). The transition metal compounds form cubic, metallic reflecting crystals (Sr₄TiP₄ (green); Sr₄TiAs₄ (silver coloured); Ba₄TiP₄ (silver coloured); Ba₄TiAs₄ (violet). They are semiconducting and very sensitive against air and moisture. The structure is a hierarchical derivative of Cr₃Si (A15) and KGe type: Cr₆Si₂ ? (□Ge₄K₄)₆(□Ge₄K₄)₂ ? (TiX₄M₄)₆(TiX₄M₄)₂, where Ti occupies the positions of the Cr₃Si structure, and the alkaline-earth metal and pnicogen atoms occupy the positions of the KGe structure. Therefore, Ti is surrounded by four X and four more distant M atoms forming a heterocubane. The mean bond lengths are: d (Ti? P) = 238.0(5) pm; 307 ? d(Sr? P) ? 333 pm; d (Ti? As) = 245.9(4); 313 ? d(Sr? As) ? 341 pm; d (Ti? P) = 240.5(5); 324 ? d(Ba? P) ? 348 pm; d (Ti? As) = 248.3(3) pm; 331 ? d(Ba? As) ? 355 pm.