β‐Y2Si2O7, a new thortveitite‐type compound,determined at 100 and 280 K

A new form of Y₂Si₂O₇ (diyttrium heptaoxodisilicate) has been synthesized which is isotypic with thortveitite, Sc₂Si₂O₇, and crystallizes in the centrosymmetric space group C2/m, both at 100 and 280 K. The Y³⁺ cation occupies a distorted octahedral site, with Y—O bond lengths in the range 2.239 (2)–2.309 (2) Å. The SiO₄ tetrahedron is remarkably regular, with Si—O bond lengths in the range 1.619 (2)–1.630 (2) Å. The bridging O atom of the Si₂O₇ pyrosilicate group shows a large anisotropic displacement perpendicular to the Si—O bond. Changes in lattice and structural parameters upon cooling are small with, however, a distinct decrease of the anisotropic displacement of the briding O atom. Structure solution and refinement in the non‐centrosymmetric space group C2 are possible but do not yield a significantly different structure model. The Si—O—Si bond angle of the isolated Si₂O₇ groups is 179.2 (1)° at 280 K in C2 and 180° per symmetry in C2/m. The C2/m structure model is favoured.     

Structural investigations and luminescence of In2Ge2O7 and In2Si2O7

The crystal structures of the ordinary pressure forms of indium digermanate In₂Ge₂O₇ and disilicate In₂Si₂O₇ have been studied from X-ray powder diffraction data by Rietveld refinement. They are closely related to that of the thortveitite which crystallizes in the monoclinic system with the space group C2/m and Z = 2. They show luminescence properties below 160 K and 200 K respectively. The luminescence is discussed in terms of crystal structure and compared to that of some other luminescent indium oxides.     

In1.08Gd0.92Ge2O7: a new member of the thortveitite family

Indium gadolinium digermanium heptaoxide, In_1.08Gd_0.92Ge₂­O₇, with a thortveitite‐type structure, has been prepared as a polycrystalline powder material by a high‐temperature solid‐state reaction. As in the mineral thortveitite, the crystal structure belongs to the monoclinic system, with space group C2/m (No. 12). The precise structural parameters were obtained by applying the Rietveld method of refinement to the X‐ray powder diffraction data. This layered structure presents, on one side, a honeycomb‐like arrangement of the unique octahedral site, which is occupied randomly by In and Gd atoms, and, on the other side, sheets of isolated Ge₂O₇ diortho‐groups made up of double tetrahedra sharing a common vertex and displaying C_2h point symmetry. This compound showed a remarkable photoluminescence effect when it was irradiated with the X‐ray beam during the X‐ray diffraction measurements, and with the α beam during the Rutherford back‐scattering spectrometry experiments employed to analyze the chemical stoichiometry.     

Crystal structure of a new digermanate: Al2Ge2O7

The structure of Al₂Ge₂O₇ has been determined by using a single crystal. The symmetry is monoclinic ($\text{C2}\text{c}\text{, Z = 4}$) with unit cell parameters a = 7.132(1) Å, b = 7.741(1) Å, c = 9.702(2) Å, β = 110.62(2)°. The structure is characterized by digermanate groups (Ge₂O₇) and by AlO₅ bipyramids with two common edges forming (AlO₃)_∞ chains. The relationship with the thortveitite structure is discussed in terms of coordination polyhedra.     

Yttrium pyrogermanate,Y2Ge2O7

The structure of diyttrium digermanate, Y₂Ge₂O₇, has been determined in the tetragonal space group P4₃2₁2. It contains one Y, one Ge (both site symmetry 1 on general position 8b) and four O atoms [one on special position 4a (site symmetry ..2) and the remaining three on general positions 8b]. The basic units of the structure are isolated Ge₂O₇ groups, sharing one common O atom and displaying a Ge—O—Ge angle of 134.9 (3)°, and infinite helical chains of pentagonal YO₇ dipyramids, parallel to the 4₃ screw axis. The crystal investigated here represents the left‐handed form of the tetragonal R₂Ge₂O₇ compounds (R = Eu³⁺, Tb³⁺, Er³⁺, Tm³⁺ and Lu³⁺).     

Penkvilksite‐2O: Na2TiSi4O11·2H2O

The crystal structure of synthetic penkvilksite‐2O, disodium titanium tetrasilicate dihydrate, Na₂TiSi₄O₁₁·2H₂O, a microporous titanosilicate, confirms the major features of a previous model that had been obtained by order–disorder (OD) theory from the known structure of penkvilksite‐1M. An important difference from the previous model involves the hydrogen bonding of the water molecule which, on the basis of a Raman spectrum and the finding of only one of the two H atoms, is proposed to be disordered about a fixed O–H direction. The structure of penkvilksite‐2O is based on (100) silicate layers linked by isolated TiO₆ octahedra to form a heteropolyhedral framework. The layer is strongly corrugated, based on interlaced spiral chains, and is crossed by two different channels that have an effective channel width of about 3 Å.     

Pyroxene‐type compounds NaM3+Ge2O6, with M = Ga,Mn, Sc and In

The four title compounds, namely sodium gallium germanate, NaGaGe₂O₆, sodium manganese vanadate germanate, NaMnV_0.1Ge_1.9O₆, sodium scandium germanate, NaScGe₂O₆, and sodium indium germanate, NaInGe₂O₆, adopt the high‐temperature structure of the pyroxene‐type chain germanates, with monoclinic symmetry and space group C2/c. The lattice parameters, the individual and average bond lengths involving M1, and the distortion parameters scale well with the ionic radius of the M1 cation. NaGaGe₂O₆ has more distorted M1 sites and more extended tetrahedral chains than NaInGe₂O₆, in which a high degree of kinking is required to maintain the connection between the octahedral and tetrahedral building units of the pyroxene structure. An exceptional case is NaMnGe₂O₆, in which the strong Jahn–Teller effect of Mn³⁺ results in more distorted octahedral sites than expected according to linear extrapolation from the other NaM³⁺Ge₂O₆ pyroxenes. In contrast with the literature, minor incorporations of V⁵⁺ in the tetrahedral site and a corresponding reduction of Mn³⁺ to Mn²⁺ in the octahedral sites in the present sample lower the Jahn–Teller distortion and stabilize the Mn‐bearing pyroxene, even allowing its synthesis at ambient pressure.     

High‐Pressure Synthesis and Single‐Crystal Structure Elucidation of the Indium Oxide‐Borate In4O2B2O7

The indium oxide‐borate In₄O₂B₂O₇ was synthesized under high‐pressure/high‐temperature conditions at 12.5 GPa/1420 K using a Walker‐type multianvil apparatus. Single‐crystal X‐ray structure elucidation showed edge‐sharing OIn₄ tetrahedra and B₂O₇ units building up the oxide‐borate. It crystallizes with Z = 8 in the monoclinic space group P2₁/n (no. 14) with a = 1016.54(3), b = 964.55(3), c = 1382.66(4) pm, and β = 109.7(1)°. The compound was also characterized by powder X‐ray diffraction and vibrational spectroscopy.     

KHCoP2O7·2H2O: a novel acidic pyrophosphate

Potassium cobalt hydrogenpyrophosphate dihydrate, KHCoP₂O₇·2H₂O, crystallizes in the orthorhombic space group Pnma. This salt is isotypic with KHMP₂O₇·2H₂O (M = Mn and Zn). The structure consists of alternating layers, built from HP₂O₇³⁻ acidic pyrophosphate groups and CoO₆ octahedra, joined by potassium ions and bridging hydrogen bonds. The Co, K and water O atoms lie on mirror planes. The pyrophosphate group consists of two symmetry‐related PO₄ groups, with the bridging O atom on a mirror plane.     

Dicalcium heptagermanate Ca2Ge7O16 revised

The structure of dicalcium heptagermanate, previously described with an orthorhombic space group, has been redetermined in the tetragonal space group . It contains three Ge positions (site symmetry 1, ..2 and 2.22, respectively), one Ca position (..2) and four O atoms, all on general 8i positions (site symmetry 1). A sheet of four‐membered rings of Ge tetrahedra (with Ge on the 8i position) and isolated Ge tetrahedra (Ge on the 4g position) alternate with a sheet of Ge octahedra (Ge on the 2d position) and eightfold‐coordinated Ca sites along the c direction in an ABABA… sequence. The three‐dimensional framework of Ge sites displays a channel‐like structure, evident in a projection on to the ab plane.     

Ho2O[SiO4] und Ho2S[SiO4]: Zwei Chalkogenid‐Derivate von Holmium(III)‐ortho‐ Oxosilicat

Ho₂O[SiO₄] and Ho₂S[SiO₄]: Two Chalcogenide Derivatives of Holmium(III) ortho‐Oxosilicate Ho₂O[SiO₄] crystallizes monoclinically with the space group P2₁/c (a = 904.15(9), b = 688.93(7), c = 667.62(7) pm, β = 106.384(8)°, Z = 4) in the A‐type structure of rare‐earth(III) oxide oxosilicates. Yellow platelet‐shaped single crystals were obtained as by‐product during an experiment to synthesize Ho₃Cl[SiO₄]₂ by reacting Ho₂O₃ and SiO₂ in the ratio 4 : 6 with an excess of HoCl₃ as flux at 1000 °C for seven days in evacuated silica ampoules. Both crystallographically different Ho³⁺ cations show coordination numbers of 8+1 and 7 with coordination figures of 2+1‐fold capped trigonal prisms and octahedra, in which one of the vertices changes to an edge by two instead of one coordinating atoms, respectively. The O^2— anion not linked to silicon is surrounded tetrahedrally by four Ho³⁺ cations which built a layer parallel (100) by vertex‐ and edge‐sharing of the [OHo₄]¹⁰⁺ units according to {[(O5)(Ho1)_1/1(Ho2)_3/3]⁴⁺}. Within rhombic meshes of these layers the isolated oxosilicate tetrahedra [SiO₄]^4— come to lie. Ho₂S[SiO₄] crystallizes orthorhombically in the space group Pbcm (a = 605.87(5), b = 690.41(6), c = 1064.95(9) pm, Z = 4). It also emerged as a single‐crystalline by‐product obtained during the synthesis of Ho₂OS₂ by reaction of a mixture of Ho₂O₃, Ho and S with the wall of the evacuated silica tube used as container with an excess of CsCl as flux at 800 °C. The structure of the yellow platelet‐shaped, air and water resistant crystals also distinguishes two Ho³⁺ cations with bicapped trigonal prisms and trigondodecahedra as coordination polyhedra for CN = 8. The S^2— anions are almost square planar surrounded by four Ho³⁺ cations, but situated completely outside this plane. The [SHo₄]¹⁰⁺ squares form strongly corrugated layers perpendicular to [100] by corner‐sharing according to {[(S)(Ho1)_2/2(Ho2)_2/2]⁴⁺}. Contrary to the oxide oxosilicates the isolated oxosilicate tetrahedra [SiO₄]^4— do not lie within the rhombic meshes of these layers, but above and below the (Ho2)³⁺ cations while viewing along [100].     

Die Kristallstruktur von Ag2Ge2O5: Eine neuartige Gerüststruktur von Ge2O52−

Crystal Structure of Ag₂Ge₂O₅: A New Ge₂O₅^2? Network Structure Ag₂Ge₂O₅ was prepared from the binary oxides at high O₂ pressures. Single crystal X-ray diffraction work indicated monoclinic symmetry (P2₁/c; a = 1101.3(2); b = 1006.3(1); c = 1221.9(3) pm; ß = 94.6(1)°). The structure was determined by direct methods (3372 independent structure factors) and refined to a conventional R value of 0.084. A new Ge₂O₅^2? network structure was found with germanium coordinated octahedrally (­d(Ge—O) = 188,7 pm) and tetrahedrally (­d(Ge—O) = 175,9 pm), in equal proportions, by oxygen. The polyhedra share vertices and edges, thus forming a three dimensional channel system, which is occupied by Ag⁺ ions. The shortest Ag—Ag distance of 284 pm, like the pale yellow colour of the compound, indicates Ag⁺—Ag⁺ interaction.     

Crystal structure of the thortveitite‐related M phase, (MnxZn1–x)2V2O7 (0.75 < x < 0.913): a combined synchrotron powder and single‐crystal X‐ray study

The determination of the crystal structure of the M phase, (Mn_xZn_1–x)₂V₂O₇ (0.75 < x < 0.913), in the pseudobinary Mn₂V₂O₇–Zn₂V₂O₇ system for x ≃ 0.8 shows that the previously published triclinic unit‐cell parameters for this thortveitite‐related phase do not describe a true lattice for this phase. Instead, single‐crystal X‐ray data and Rietveld refinement of synchrotron X‐ray powder data show that the M phase has a different triclinic structure in the space group P with Z = 2. As prior work has suggested, the crystal structure can be described as a distorted version of the thortveitite crystal structure of β‐Mn₂V₂O₇. A twofold superstructure in diffraction patterns of crystals of the M phase used for single‐crystal X‐ray diffraction work arises from twinning by reticular pseudomerohedry. This superstructure can be described as a commensurate modulation of a pseudo‐monoclinic basis structure closely related to the crystal structure of β‐Mn₂V₂O₇. In comparison with the distortions introduced when β‐Mn₂V₂O₇ transforms at low temperature to α‐Mn₂V₂O₇, the distortions which give rise to the M phase from the β‐Mn₂V₂O₇ prototype are noticeably less pronounced.     

K4Au7Ge2: eine Gerüststruktur mit Au7-Doppeltetraedern und Ge2-Hanteln

K₄Au₇Ge₂: a Framework Structure with Au₇-Double-Tetrahedra and Ge₂-Dumb-Bells Black lustrous, brittle single crystals of a hitherto unknown K₄Au₇Ge₂ were synthesized by the reaction of KN₃, germanium- and gold-powder at 550°C. The structure was determined from X-ray single-crystal diffractometry data: space group R3 m, Z = 3, a = 6.411(3) Å, c = 27.912(20) Å, R/R_w(w = 1) = 0.046/0.056, Z(F ${}_{\text{º}}^{\text{2}}$ ) ≥ 3σ(F ${}_{\text{º}}^{\text{2}}$ ) = 302 and N(var.) = 18. K₄Au₇Ge₂ crystallizes in a substitution variant of the MgCu₂-type. Gold and germanium form a framework structure that consists of corner-sharing Au₇-double-tetrahedra and Ge₂-dumb-bells. The potassium atoms occupy channel-like cavities within the gold germanium partial structure.     

Die Kristallstruktur der Verbindung Cd2Ge7O16

The crystal structure of Cd₂Ge₇O₁₆ has been determined by means of three-dimensional single-crystal data. A finalR-value of 6.3% was obtained by least squares refinement based on 230 observed reflexions. The tetragonal unit cell with the lattice parametersa=11.31 andc=4.63 Å contains two formula units Cd₂Ge₇O₁₆. The compound is built up by [GeO₄]-tetrahedra and [GeO₆]-octahedra forming a three-dimensional framework with the Cd atoms located in the cavities. The average interatomic distances are found to be: Ge–O=1.74 (tetrahedra), 1.89 (octahedra) and Cd–O=2.36 Å.

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