Contributions on thermal behaviour and crystal chemistry of anhydrous phosphates. XIX. Tri-chromium(II)-bis-phosphate Cr3(PO4)2 (≙ Cr6(PO4)4) – A transition metal(II)-orthophosphate with new structure type

Deep blue-violet single crystals of hitherto unknown chromous orthophosphate have been obtained reducing CrPO₄ by elemental Cr at temperatures above 1050°C in evacuated silica ampoules (NH₄I or I₂ as mineraliser). The complex structure of Cr₃(PO₄)₂ (P2₁2₁2₁, Z = 8, a = 8.4849(10) Å, b = 10.3317(10) Å, c = 14.206(2) Å) contains six crystallographically independent Cr²⁺ per unit cell. Five of them are coordinated by four oxygen atoms which form a distorted (roof shaped) square plane as first coordination sphere at interatomic distances 1.96 Å ? d(Cr? O) ? 2.15 Å. Their coordination is completed by additional oxygen atoms (2 or 3) at distances 2.32 Å ? d(Cr? O) ? 3.21 Å. The sixth Cr²⁺ shows six-fold octahedral coordination with strong radial distortion (d(Cr? O): 1.97, 2.04, 2.15, 2.28, 2.29, 2.53 Å). The four different [PO₄] groups exhibit only minor deviations from ideal tetrahedral geometry (1.51 Å ? d(P? O) ? 1.57 Å, 104.3° ? ∠(O? P? O) ? 114.4°). An unusually low magnetic moment μ_exp = 4.28(2) μ_B (θ_P = ?54.8(5) K) has been observed for Cr²⁺.     

Neue Metalloxide mit Tetraeder-Doppel als Baugruppe: Rb6[Tl2O6] und Cs6[In2O6]

New Metal Oxides with Doubles of Tetrahedra as Building Units: Rb₆[Tl₂O₆] and Cs₆[In₂O₆] We prepared the hitherto unknown Rb₆[Tl₂O₆] and Cs₆[In₂O₆] by heating mixtures of Tl₂O₃ and RbO_0.60 (Rb:Tl = 3.5:1) as well as In₂O₃ and CsO_0.53 (Cs:In = 3.5:1) as single crystals [closed Ag-cylinder, 650°C, 14 d]. The single crystals of Rb₆[Tl₂O₆] are yellow, those of Cs₆[In₂O₆] pale yellow, all transparent and rude. The new type of structure was elucidated by 4-circle-diffractometer (PW 1100) data. Rb₆[Tl₂O₆]: P2₁/a; a = 1145,7(3), b = 713,3(1), c = 783,9(2) pm, β = 93,73° (2), Z = 2; Ag–Kα, 2100 out of 2531 I₀(hkl), R = 9,6% and R_w = 8,9%. Cs₆[In₂O₆]: P2₁/a; a = 1178,5(4), b = 730,7(2), c = 816,3(2) pm, β = 95,38° (3), Z = 2; Mo–Kα, 1584 out of 2032 I₀(hkl), R = 9,25%, and R_w = 8,44%. The Madelung Part of Lattice Energy, MAPLE, is calculated and discussed.     

Beiträge zum thermischen Verhalten wasserfreier Phosphate. IX. Darstellung und Kristallstruktur von Cr6(P2O7)4. Ein gemischtvalentes Pyrophosphat mit zwei- und dreiwertigem Chrom

Contributions on the Thermal Behaviour of Anhydrous Phosphates. IX. Synthesis and Crystal Structure of Cr₆(P₂O₇)₄. A Pyrophosphate Containing Di- and Trivalent Chromium Cr₆(P₂O₇)₄ (Cr₂²⁺Cr₄³⁺(P₂O₇)₄) can be obtained reducing CrPO₄ by phosphorus (950°C, 48 h, 100 mg iodine as mineralizer). By means of chemical transport reactions (transport agent iodine; 1050 → 950°C) the compound has been separated from its neighbour phases (Cr₂P₂O₇, CrP₃O₉) and crystallized (greenish, transparent crystals; edge length up to 0.3 mm). The crystal structure of Cr₆(P₂O₇)₄ (Spcgrp.: P-1; z = 1; a = 4.7128(8) Å, b = 12.667(3) Å, c = 7.843(2) Å, α = 89.65(2)°, β = 92.02(2)°, γ = 90.37(2) has been solved and refined from single crystal data (2713 unique reflections, 194 parameter, R = 0.035). Cr²⁺ is surrounded by six oxygen atoms which occupy the corners of an elongated octahedron (4 × d^{Cr? O} ≈? 2.04 Å; 2 × d^{Cr? O} ≈? 2.62 Å). The Cr³⁺ ions are also coordinated octahedraly (1.930 Å ≤ d_{Cr? O} ≤ 2.061 Å). The crystallographically independent pyrophosphate groups show nearly eclipsed conformation. The bridging angles (P? O? P) are 136.5° and 138.9° respectively.     

Zum chemischen Transport von Chrom- und Manganmonophosphid mit Iod. Experimente und Modellrechnungen

On the Chemical Vapour Transport of Chromium and Manganese Monophosphide. Experimental Results and Thermochemical Calculations Using iodine as transport agent well shaped crystals of a volume up to V ≈︁ 50 mm³ (CrP) or an edgelength of approximately 1 ≈︁ 10 mm (MnP) can be grown. CrP has been deposited at the lower temperature of a temperature gradient (1050 → 950°C). At a density of the transport agent higher than D = 26 · 10⁻⁶ [mol I₂/cm³] CrP and CrI_2,1 coexist in the deposition region at the lower temperature. The determined composition of the condensed phases under equilibrium conditions are in accordance with thermochemical calculations assuming the heat of formation of CrP to be Δ_FH= −25.5 ± 2 [kcal/mol]. Furthermore these calculations show that the solution of CrP in the gas phase leads to CrI_2,g, Cr₂I_4,g, P_2,g and P_4,g, while I_2,g, HI_g, PI_3,g and P₂I_4,g have to be considered as transport agents. The migration of MnP (1000 → 1100°C) results from an exothermic reaction. MnP_s exists besides MnI_2,1 in the source region. Thermochemical calculations are in good agreement with the experimental results and suggest the following heterogenous equilibrium to be responsible for the observed behaviour: .     

Genes involved in <Emphasis Type="Italic">Drosophila</Emphasis>glutamate receptor expression and localization

Background  

A clear picture of the mechanisms controlling glutamate receptor expression, localization, and stability remains elusive, possibly due to an incomplete understanding of the proteins involved. We screened transposon mutants generated by the ongoing Drosophila Gene Disruption Project in an effort to identify the different types of genes required for glutamate receptor cluster development.