M. Somer

BISMUT(II)-CHALKOGENOMETALLATE(III) BI2M4X8, VERBINDUNGEN MIT BI24+-HANTELN (M = AL, GA; X = S, SE)

Die ternaren Bismut(II)-chalkogenometallate(III) Bi2M4X8 mit M = Al, Ga und X = S, Se wurden aus den binaren Chalkogeniden M2X3 und Bi2X3 sowie elementarem Bismut synthetisiert. Alle Verbindungen sind diamagnetische Halbleiter mit Eg (opt.) = 1.8–2.7 eV. Sie sind bis auf Bi2Al4Se8 thermodynamisch stabil und zerfallen oberhalb 965–1020 K peritektisch. Bi2Al4Se8 ist unterhalb 825 K metastabil und kann nur durch rasches Abkuhlen von T > 825 K erhalten werden. Die Verbindungen sind isotyp und kristallisieren in einem neuen tetragonalen tP28-Strukturtyp (P4/nnc). Besonderes Merkmal ist das bisher unbekannte Clusterkation Bi24+ mit der mittleren Bindungslange d(Bi–Bi) = 314.2 pm, der Ramanfrequenz νs = 102–108 cm–1 und der Kraftkonstante f = 0.68 N · cm–1. Die Elektronenlokalisierungsfunktion (ELF) zeigt die kovalente Bindung der Bi2-Paare, die einsamen Elektronenpaare der ψ-oktaedrisch koordinierten Bi(II)-Kationen und den polaren Charakter der Bi–X-Bindungen. Bismuth(II) Chalcogenometallates(III) Bi2M4X8, Compounds with Bi24+ Dumbbells (M = Al, Ga and X = S, Se) The ternary bismuth(II) chalcogenometallates(III) Bi2M4X8 (with M = Al, Ga and X = S, Se) were synthesized from the binary chalcogenides M2X3 and Bi2X3 and elementary bismuth. All compounds are diamagnetic semiconductors with Eg (opt.) = 1.8–2.7 eV. The phases (except Bi2Al4Se8) are thermodynamically stable and decompose peritectically above 965–1020 K. Bi2Al4Se8 is metastable below 825 K and is obtained only by rapid quenching from T > 825 K. The isotypic compounds crystallize in a new tetragonal tP28 structure type (P4/nnc). The characteristic unit is the hitherto unknown clustercation Bi24+, with the mean bond length d(Bi–Bi) = 314.2 pm, the Raman frequency 102 cm–1 ≤ νs ≤ 108 cm–1, and the mean force constant of f = 0.68 N · cm–1. The Electron Localization Function, ELF, shows the covalent Bi–Bi bond, the lone electron pairs of the ψ-octahedrally coordinated Bi(II) cations, and the polar character of the Bi–X bonds.

Darstellung, Kristallstruktur und Schwingungsspektren von Cs3As7 und Cs3(NH3)As7/Syntheses, Crystal Structure and Vibrational Spectra of Cs3As7 and Cs3(NH3)As7

Cs3As7, a compound with cage-like As73- anions, has been prepared from the elements in sealed quartz ampoules at 820 K. The ruby-red compound undergoes a first order phase transition at 640 K and is obtained as microcrystalline samples. The structure of the low-temperature α-modification is not known, but β-Cs3As7 belongs to the plastically crystalline β-Rb3P7 type of structure (F m 3̄ m , a (673 K) = 1169,2(1) pm). Cs3As7 melts under its own vapour pressure at 1061 K, and is easily soluble in liquid ammonia. From those solutions ruby red crystals of Cs3(NH3)As7 precipitate. In dynamical vacuum NH3 is evaporated in the region of 300 to 520 K, resulting in Cs3As7. Cs3(NH3)As7 crystallizes in the space group P21/a (a = 2759.0(12) pm, b = 744.1(3) pm, c = 751.5(3) pm, β = 90.16(5)°; Z = 4). The structure is closely related to the plastically crystalline β-Rb3P7 type structure (Li3Bi variant). The heptaarsanortricyclene anion is coordinated by cesium atoms, connecting the anions to a three dimensional arrangement. The anion exhibits a differentiation of As - As bond lengths typical for ionic nortricyclenes (d(basis) = 251.2 pm; d(basis-bridge) = 235.5 pm; d(bridge-bridgehead) = 240.1 pm). The distances Cs to As are in the range 372 to 401 pm. The cesium atoms are surrounded by three resp. four As atoms and the NH3 molecules. The FIR and Raman spectra are given for different temperatures as well as of an en-solution of Cs3(NH3)As7. The valence vibrations of NH3 are found at 3175 (A1) and 3320 cm-1 (E ). The fundamental vibrations of the three-membered ring of different heteronortricyclenes with P and As are compared and yield a correlation factor χ = 0.57(1) for the observed frequencies between P3 and As3. The band gaps EG are determined from the diffuse reflexion at 2.14 eV for Cs3(NH3)As7 and 2.00 eV for Cs3As7.

Linear anions [CuAs2]5-, [AuP2]5- and [AuAs2]5- in potassium compounds

Abstract K5[AuP2], K5[AuAs2] and K5[CuAs2] were prepared from molten mixtures of the elements under an argon atmosphere in sealed niobium ampoules. The compounds form shiny black plates which are sensitive to moisture. The crystal structures of the three isotypic compounds were refined from X-ray single-crystal data. The characteristic units are linear anions [As-Cu-As]5-, [P-Au-P]5- and [As-Au-As]5- with bond lengths CuAs = 230.7(2) pm, AuP = 236.8(9) pm and AuAs = 246.0(3) pm respectively, enclosed in a distorted hexagonal close packing of the potassium cations. The structural relationship to the K5[CuSb2] and Na4[HgP2] types is discussed concerning the cation polyhedra. The FIR spectra of the compounds are measured, the assignment of the observed frequencies being based on the D∞h symmetry of the isolated [X-T-X]5− units. The crystallographic data are as follows: space group P63/mmc (no. 194), Z = 2; K5[CuAs2] − a = 537.7(2) pm, c = 1877.1(4) pm, c/a = 3.49; K5[AuP2] − a = 563.6(2) pm, c = 1871.6(4) pm, c a = 3.32 ; K5[AuAs2] − a = 573.0(2) pm, c = 1921.6(4) pm, c a = 3.35 .

Crystal structure of potassium catena-di-μ-arsenido niccolate, K2(NiAs2)

Source of material: Title compound was prepared from a stoichiometric mixture of the elements in an evacuated and sealed silica tube at 950 K. A crucible of A1203 was used to avoid reaction with the silica ampoule. The Ni atoms are square planar coordinated by four Ρ atoms. Each Ρ atom has one Ρ and two Ni neighbours within the infinite [NiP2]~ chain. The bond lengths d(Ni-P) and d(P-P) are: 2.265(2) Ä and 2.187(4) A, respectively·

Crystal structure of tribarium tetraphosphidodiindate, ВазIn2Р4

ФВа2 Ba1 Source of material: Ваз1п2Р4 was first obtained as a by-product during attempts to synthesize Bai4lnPi i (see ref. 1 ) by varying the ratio of the educts BaP, In and Ρ as well as the reaction conditions. Pure Ваз1п2Р4 can be prepared from a mixture of BaP and InP (ratio 3:2) in sealed niobium ampoule at 1325 K. The crystal stnicture of Ваз1п2Р4 consists of pairs of edge-sharing tetrahedra [In2P2P4/2]6(d(In-P) = 2.569 Â 2.645 Â), which are linked via common vertices to layers parallel to ( 1(Ю). The partial structure Ва(2)1п2Р4 is similiar to that of SrIn2Se4 (see ref. 2) and GeCd2As4 (see ref. 3). The other Ba atoms, Ba(l), open the phosphorus framework occupying the so created new octahedral sites. Ваз1п2Р4 is isostructural with Ca3Al2As4 (see ref.4).

Crystal structure of tristrontium tetraphosphidodialuminate, Sг3Аl2Р4

Source of material: 8гзА12Р4 was formed as a by-product of the Ка5г2[А1Рз] synthesis (see ref. 1). Pure 8гзА12Р4 was prepared from a stoichiometric mixture of SrP and AIP (ratio: 3:2) in an alumina crucible enclosed in steel ampoule at 1375 K. The crystal structure of 8гзА12Р4 consists of pairs of edge-sharing tetrahedra [Al2P2P4ß]^ (d(Al-P) = 2.377 A 2.443 Â), which are linked via commcm vertices to layers parallel ( 1 0 0) (see refs. 2 and3).

[Al2P4]6-, [Al2As4]6-, [Ga2P4]6- und [Ga2As4]6-, Zintl-Anionen mit 1,3-Dimethylencyclobutan-Struktur / [Al2P4]6-, [Al2As4]6-, [Ga2P4]6- and [Ga2As4]6-, Zintl Anions with 1.3-Dimethylene-cyclobutane Structure

The compounds Cs6M2X4 (M = Al, Ga; X = P, As) were synthesized from stoichiometric mixtures of Cs, M and Cs4X6 in sealed Nb ampoules at 950 K. They are isotypic and crystallize in the monoclinic space group P21/c (No. 14) with Z = 4 formula units per unit cell. The anion partial structure is characterized by isolated [M2X4]6- units with relatively short distances for the terminal d(M–X) bonds corresponding to a Pauling Bond Order PBO = 1.5. The distances d(M–X) of the four-membered M2X2 rings correspond to single bonds. The FIR spectra have been interpreted on the basis of the [M2X4]6- units with 2/m 2/m 2/m-D2h, symmetry by considering a factor group splitting. The assignment of the observed frequencies is supported by a normal coordinate analysis.

Crystal structure of caesium potassium di-μ-arsenido-bis(arsenidogallate), Cs5.23K0.77Ga2As4

Source of material: The compound may be prepared from Κ As, GaAs and Cs (1:1:3) in a sealed Nb-ampoule at 950 K. The excess of alkali metals (Cs and K) is removed by high vacuum distillation at 525 K. The anionic partial structure of the compound is characterized by the slightly bent dimeric anions [Ga2As4]~ (see réf. 1 and ref. 2) with the average bond lengths (Ga-As)eio = 2.336(3) Â and d(Ga-As)end0 = 2.462(3) Â (see ref. 3).