Über quaternäre Oxoplumbate(IV). Zur Kenntnis von Rb2Li14[Pb3O14] und Cs2Li14[Pb3O14]

On Quaternary Oxoplumbates(IV). On the Knowledge of Rb₂Li₁₄[Pb₃O₁₄] and Cs₂Li₁₄[Pb₃O₁₄] For the first time, Rb₂Li₁₄[Pb₃O₁₄] and Cs₂Li₁₄[Pb₃O₁₄] have been prepared by heating of mixtures of Li₂O, β-?PbO₂”? and Rb₂PbO₃, Cs₂PbO₃ respectively with Li:Pb:A = 14:3:2, (A = Rb, Cs). [Ag-cylinders, sealed under vacuum in Duran-glass ampoule, 590 and 550°C, 40 d, powder (650°C, 200 d, single crystals of Rb₂Li₁₄[Pb₃O₁₄])]. Rb₂Li₁₄[Pb₃O₁₄] is nearly colourless with ivory nuance, Cs₂Li₁₄[Pb₃O₁₄] is pale yellow. According to powder and single crystal investigations, both are isotypic with K₂Li₁₄[Pb₃O₁₄]. Structure refinement of Rb₂Li₁₄[Pb₃O₁₄]: 1015 symmetry independent reflexions, four-circle-diffraktometer PW 1100 (Fa. Philips), ω-scan, MoKα, R = 5.73%, R_W = 5.33%, absorption not considered, space group Immm with a = 1284.71(9), b = 793.90(4), c = 727,35(5) pm, d_x-ray = 4.99 g · cm^?3, d_pyc = 5.01 g · cm^?3, Z = 2. Cs₂Li₁₄[Pb₃O₁₄]: a = 1295.28(12), b = 796.69(8), c = 732.44(7) pm, d_x-ray = 5.31 g · cm^?3, d_pyc = 5.28 g · cm^?3, Z = 2. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Effective Ionic Radii, MEFIR, are calculated.     

[O2Pb3]2(BO3)Br: An Oxidoborate Oxide Bromide with the ∞1[O2Pb3] Double Chains Based on Edge‐sharing OPb4 Tetrahedra

Through extensive research on the PbO / PbBr₂ / B₂O₃ system, a new single crystal of yellow lead‐containing oxyborate bromine, [O₂Pb₃]₂(BO₃)Br, was grown from the melt. It crystallizes in the centrosymmetric space group Cmcm (no. 63) of the orthorhombic system with the following unit cell dimensions: a = 9.5748(8) Å, b = 20.841(2) Å, c = 5.7696(5) Å, and Z = 4. The whole structure is characterized by an infinite one‐dimensional (1D) _∞¹[O₂Pb₃] double chain, which is based on the OPb₄ oxocentered tetrahedra and considered as the derivative of the continuous sheet of OPb₄ tetrahedra from the tetragonal modification of α‐PbO. The 1D _∞¹[O₂Pb₃] double chains are further bridged by the BO₃ units through common oxygen atoms to form two‐dimensional (2D) _∞¹[[(O₂Pb₃)(BO₃)] layers, with Br atoms situated between the layers. IR spectroscopy, UV/Vis/NIR diffuse reflectance spectroscopy, and thermal analysis were also performed on the reported material.     

La4(Si5.2Ge2.8O18)(TeO3)4 and La2(Si6O13)(TeO3)2: Intergrowth of the lanthanum(III) tellurite layer with the XO4 (X=Si/Ge) tetrahedral layer

Two novel lanthanum(III) silicate tellurites, namely, La₄(Si_5.2Ge_2.8O₁₈)(TeO₃)₄ and La₂(Si₆O₁₃)(TeO₃)₂, have been synthesized by the solid state reactions and their structures determined by single crystal X-ray diffraction. The structure of La₄(Si_5.2Ge_2.8O₁₈)(TeO₃)₄ features a three-dimensional (3D) network composed of the [(Ge_2.82Si_5.18)O₁₈]⁴⁻ tetrahedral layers and the [La₄(TeO₃)₄]⁴⁺ layers that alternate along the b-axis. The germanate-silicate layer consists of corner-sharing XO₄ (X=Si/Ge) tetrahedra, forming four- and six-member rings. The structure of La₂(Si₆O₁₃)(TeO₃)₂ is a 3D network composed of the [Si₆O₁₃]²⁻ double layers and the [La₂(TeO₃)₂]²⁺ layers that alternate along the a-axis. The [Si₆O₁₃]²⁻ double layer is built by corner-sharing silicate tetrahedra, forming four-, five- and eight-member rings. The TeO₃²⁻ anions in both compounds are only involved in the coordination with La³⁺ ions to form a lanthanum(III) tellurite layer. La₄(Si_5.2Ge_2.8O₁₈)(TeO₃)₄ is a wide band-gap semiconductor.     

Syntheses and crystal structures of two new hydrated borates, Zn8[(BO3)3O2(OH)3] and Pb[B5O8(OH)]·1.5H2O

Two new hydrated borates, Zn₈[(BO₃)₃O₂(OH)₃] and Pb[B₅O₈(OH)]·1.5H₂O, have been prepared by hydrothermal reactions at 170 °C. Single-crystal X-ray structural analyses showed that Zn₈[(BO₃)₃O₂(OH)₃] crystallizes in a non-centrosymmetric space group R32 with a=8.006(2) Å, c=17.751(2) Å, Z=3 and Pb[B₅O₈(OH)]·1.5H₂O in a triclinic space group P1¯ with a=6.656(2) Å, b=6.714(2) Å, c=10.701(2) Å, α=99.07(2)°, β=93.67(2)°, γ=118.87(1)°, Z=2. Zn₈[(BO₃)₃O₂(OH)₃] represents a new structure type in which Zn-centered tetrahedra are connected via common vertices leading to helical ribbons _∞¹[Zn₈O₁₅(OH)₃]¹⁷⁻ that pack side by side and are further condensed through sharing oxygen atoms to form a three-dimensional _∞³[Zn₈O₁₁(OH)₃]⁹⁻ framework. The boron atoms are incorporated into the channels in the framework to complete the final structure. Pb[B₅O₈(OH)]·1.5H₂O is a layered compound containing double ring [B₅O₈(OH)]²⁻ building units that share exocyclic oxygen atoms to form a two-dimensional layer. Symmetry-center-related layers are stacked along the c-axis and held together by interlayer Pb²⁺ ions and water molecules via electrostatic and hydrogen bonding interactions. The IR spectra further confirmed the existence of both triangular BO₃ and OH groups in Zn₈[(BO₃)₃O₂(OH)₃], and BO₃, BO₄, OH groups as well as guest water molecules in Pb[B₅O₈(OH)]·1.5H₂O.     

Die kristallstruktur des kaliumtetragermanats K2[Ge4O9]

Zusammenfassung Die Kristallstruktur des Kaliumtetragermanats, K₂[Ge₄O₉], wurde mit Hilfe dreidimensionaler Röntgendaten bestimmt. K₂[Ge₄O₉] kristallisiert trigonal mit der Raumgruppe P033034c1 (Nr. 165) und den Gitterparametern:a=11.84 undc=9.80 Å. Die vorgeschlagene strukturchemische Beziehung zum Wadeit, K₂Zr[Si₃O₉], wird durch die Existenz tetraedrischer [Ge₃O₉]-Ringe, die über [GeO₆]-Oktaeder zu einem dreidimensionalen Gerüst verknüpft sind, bestätigt. Es wurden folgende mittlere Ge–O-Abstände gefunden: 1.762 (Tetraeder) und 1.886 Å (Oktaeder).

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The crystal structure of potassium tetragermanate K₂[Ge₄O₉]

The crystal structure of potassium tetragermanate K₂[Ge₄O₉] has been determined by means of three-dimensional x-ray data. K₂[Ge₄O₉] crystallizes trigonal with space group P033034c1 (No. 165) and lattice parametersa=11.84 andc=9.80 Å. The proposed structural relationship to wadeite K₂Zr[Si₃O₉] is confirmed by the existence of [Ge₃O₉] rings built by tetrahedra, which are linked by [GeO₆] octahedra forming a three-dimensional network. The mean Ge–O distances are found to be: 1.762 (tetrahedra) and 1.886 Å (octahedra).

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Mit 2 Abbildungen

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Herrn Prof. Dr.H. Nowotny in Verehrung gewidmet.     

Synthesis,crystal structure and electrical characterization of Cs4[(UO2)2(V2O7)O2], a uranyl divanadate with chains of corner-sharing uranyl square bipyramids

A new cesium uranyl vanadate Cs₄[(UO₂)₂(V₂O₇)O₂] has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the orthorhombic symmetry with space group Pmmn and following cell parameters: a=8.4828(15) Å, b=13.426(2) Å and c=7.1366(13) Å, V=812.8(3) Å³, Z=2 with ρ_mes=5.39(2) g/cm³ and ρ_cal=5.38(1) g/cm³. A full-matrix least-squares refinement on the basis of F² yielded R₁=0.027 and wR₂=0.066 for 62 parameters with 636 independent reflections with I⩾2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a charge-coupled device detector. The crystal structure is characterized by _∞²[(UO₂)₂(V₂O₇)O₂]⁴⁻ corrugated layers parallel to (001). The layers are built up from distorted (UO₂)O₄ octahedra and divanadate V₂O₇ units resulting from two VO₄ tetrahedra sharing corner. The distorted uranyl octahedra (UO₂)O₄ are linked by corners to form infinite _∞¹[UO₅]⁴⁻ chains parallel to the a-axis. These chains are linked together by symmetrical divanadate units sharing two corners with each chain, the two last corners being oriented towards the same interlayer. The cohesion of the structure is assured by interlayer Cs⁺ ions. Their mobility within the interlayer space gives rise to a cationic conductivity with an important jump between 635°C and 680°C. Cs₄[(UO₂)₂(V₂O₇)O₂] is readily decomposed by water at 60°C to form the Cs-carnotite analog Cs₂(UO₂)₂(V₂O₈) compound.     

Pr4S3[Si2O7] und Pr3Cl3[Si2O7]: Durch weiche Fremdanionen modifizierte Derivate von Praseodymdisilicat

Pr₄S₃[Si₂O₇] and Pr₃Cl₃[Si₂O₇]: Derivatives of Praseodymium Disilicate Modified by Soft Foreign Anions For synthesizing both the disilicate derivatives Pr₄S₃[Si₂O₇] and Pr₃Cl₃[Si₂O₇], Pr, Pr₆O₁₁ and SiO₂ are brought to reaction with S and PrCl₃, respectively, in suitable molar ratios (850 °C, 7 d) in evacuated silica tubes. By using NaCl as a flux, Pr₄S₃[Si₂O₇] crystallizes as pale green, transparent single crystals (tetragonal, I4₁/amd, a = 1201.6(1), c = 1412.0(2) pm, Z = 8) with the appearance of slightly compressed octahedra. On the other hand, Pr₃Cl₃[Si₂O₇] emerges as pale green, transparent platelets and crystallizes monoclinically (space group: P2₁, a = 530.96(6), b = 1200.2(1), c = 783.11(8) pm, β = 109.07(1)°, Z = 2). In both crystal structures ecliptically conformed [Si₂O₇]^6– units of two corner‐linked [SiO₄] tetrahedra with Si–O–Si bridging angles of 131° in the sulfide and 148° in the chloride disilicate are present. In Pr₄S₃[Si₂O₇] both crystallographically independent Pr³⁺ cations show coordination numbers of 8 + 1 (5 S^2– and 3 + 1 O^2–) and 9 (3 S^2– and 6 O^2–). For Pr1, Pr2 and Pr3 in Pr₃Cl₃[Si₂O₇] coordination numbers of 10 (5 Cl^– and 5 O^2–) and 9 (2 ×; 4 Cl^– and 5 O^2– or 3 Cl^– and 6 O^2–, respectively) occur.     

Neue Cyclosilicate der Alkalimetalle: Cs5AgSi3O9 und Cs6Na6Si6O18

New Alkali Cyclosilicates: Cs₅AgSi₃O₉ and Cs₆Na₆Si₆O₁₈ The new cyclosilicates were obtained from reactions of the binary oxides at 450–500 °C under inert gas atmosphere. Cs₅AgSi₃O₉ crystallizes in the space group P2₁/m with the lattice constants a = 968,2(2) pm, b = 652,7(1) pm, c = 1162,6(3) pm, β = 93,84(2)° and Cs₆Na₆Si₆O₁₈ in R‐3m with a = 1208,0(1) pm, c = 1458,9(2) pm (IPDS data sets). The characteristic features are isolated rings, [Si₃O₉]^6– and [Si₆O₁₈]^12–, respectively. In Cs₅AgSi₃O₉ these are connected via Ag⁺ to chains. Layers of [NaO₄]‐tetrahedra separate the hexameric rings in Cs₆Na₆Si₆O₁₈. Coordination numbers of caesium are observed between C.N. 3 and C.N. 9 in these alkali rich cyclosilicates. MAPLE calculations of both cyclosilicates as well as the absorption and IR spectrum of Cs₅AgSi₃O₉ are presented. Preparative and thermoanalytical techniques have been used to investigate the reactivity of Cs₅AgSi₃O₉ in the presence of cobalt and nickel metal.     

Ca3ZnGeO2[Ge4O12]: a Ca–Zn germanate related to the mineral taikanite

The title compound, Ca₃ZnGeO₂[Ge₄O₁₂] (tricalcium zinc germanium dioxide dodecaoxidotetragermanate), adopts a taikanite‐type structure. The tetrahedral [Ge₄O₁₂] chain geometry is very similar to that of the silicate chain of taikanite, i.e. BaSr₂Mn³⁺₂O₂[Si₄O₁₂], while the major difference is found parallel to the c axis. In taikanite, Mn³⁺ octahedra form an infinite zigzag chain, whereas the title compound has a chain of distorted ZnO₆ octahedra, which alternates with distorted GeO₄ tetrahedra connected to each other via two common edges. Eightfold‐coordinated Ca²⁺ polyhedra and ZnO₆ octahedra form a slab parallel to (001) which alternates with another slab containing the tetrahedrally coordinated Ge sites along the c axis.     

Methanolothermal Synthesis and Structures of the Quaternary Group 14 – Group 15 Cesium Selenidometalates Cs3AsGeSe5 and Cs4Ge2Se6

Cs₃AsGeSe₅ and Cs₄Ge₂Se₆ can be prepared by methanolothermal reaction of elemental As, Ge and Se with Cs₂CO₃ at 190 °C. The former quaternary phase contains zweier [{AsGeSe₅}^3?] chains consisting of corner‐bridged GeSe₄ tetrahedra and AsSe₃ pyramids and represents the first Ge^IV‐As^III chalcogenidometalate. Cs₄Ge₂Se₆ exhibits discrete [Ge₂Se₆]^4? anions formed by two edge‐sharing GeSe₄ tetrahedra.     

Neue Vertreter des K2Li14[Pb3O14]-Typs Cs2Li14[Tb3O14] und K2Li14[Zr3O14] [1, 2]

Inhaltsübersicht. Erstmals wurden klar durchscheinende, orange-farbene Einkristalle von Cs₂Li₁₄[Tb₃O₁₄] aus Cs₂TbO₃ und Li₂O (Tb: Li = 1:5) dargestellt [550°C, 21 d, verschlossenes AuRohr]. Es liegt der K₂Li₁₄[Pb₃O₁₄]-Typ vor [Vierkreisdiffraktometerdaten, PW 1100, MoKä-Strahlung, 660 I_o(hkl), R = 4,8%, R_w = 3,4%, Immm, a = 1293,5(8), b = 792,6(3), c = 740,4(3) pm, Z = 2, d_rö = 4,65]. Ebenfalls neu wurde K₂Li₁₄[Zr₃O₁₄] in Form farbloser Einkristalle durch Tempern inniger Gemenge von K₂O, Li₂O und ZrO₂ (K: Li: Zr = 1:4:1,5) dargestellt [900°C, 14 d, geschlossene Ni-Bombe] und röntgenographisch untersucht. Die Strukturverfeinerung [612 I_o(hkl), Vierkreisdiffraktometerdaten, PW 1100, MoKα-Strahlung, R = 5,9%, R_w = 5,3%, Immm, a = 1244,6, b = 776,4, c = 724,3 pm, Z = 2] bestätigt die Isotypie mit K₂Li₁₄[Pb₃O₁₄]. Der Madelunganteil der Gitterenergie, MAPLE, Effektive Koordinationszahlen, ECoN, diese über Mittlere Effektive Ionenradien, MEFIR, wurden berechnet. Für die nun bekannten Vertreter dieses Typs wurde ein Isotypievergleich vorgenommen. New Compounds of the K₂Li₁₄[Pb₃O₁₄] Type: Cs₂Li₁₄[Tb₈O₁₄] and K₂Li₁₄[Zr₃O₁₄] For the first time Cs₂Li₁₄[Tb₃O₁₄] has been prepared as orange single crystals from Cs₂TbO₃ and Li₂O (Tb: Li = 1:5) [550°C, 21 d, sealed Au-Tube]. Structure Refinement [four-circle diffractometer data, PW 1100, MoKα radiation, 660 I_o(hkl), R = 4.8%, R_w = 3.4%, Immm, a = 1293.5(8), b = 792.6(3), c = 740.4(3) pm, Z = 2, d_rö = 4.65] confirms isotypy with K₂Li₁₄[Pb₃O₁₄]. K₂Li₁₄[Zr₃O₁₄] has also been prepared as colorless single crystals from K₂O, Li₂O, and ZrO₂ (K: Li: Zr = 1:4:1.5), [900°C, 14 d, closed Ni-cylinder] and investigated by x-ray [612 I_o(hkl), four-circle diffractometer data, PW 1100, MoKα radiation, R = 5.9%, R_w = 5.3%, Immm, a = 1244.6, b = 776.4, c = 724.3 pm, Z = 2]. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, the latter derived from Mean Effective Fictive Ionic Radii, MEFIR, are calculated. A detailed comparison of the structures is carried out.     

Crystal structure of Pb3O2(OH)Br,a Br-analogue of damaraite

The crystal structure of Pb₃O₂(OH)Br (orthorhombic, Pmc2₁, a=5.8447(8), b=7.0715(10), c=15.309(2) Å, V=632.75(15) Å³) has been solved by direct methods and refined to R₁=0.046 (wR=0.077). The structure is based on [O₂Pb₃] chains of edge-sharing OPb₄ oxocentered tetrahedra that extend parallel to the a axis and occur in two orientations inclined to each other by ∼50°. The [O₂Pb₃] chains are linked through OH(3) groups to form an [Pb₃O₂](OH) sheet that is parallel to (010). Additional OH(4) groups are attached to the [O₂Pb₃] chains. The OH groups form two short (OH)Pb bonds that results in (OH)Pb₂ dimers.     

Die Kristallstruktur von Si5O[PO4]6

The crystal structure of Si₅O[PO₄]₆ has been determined and refined by least-squares, using three-dimensional X-raydata fromWeissenberg photographs: space group R 3;a=7.86₉ andc=24.13₈ Å;Z=3; 418 independent reflections;R=6.0%. The crystal structure consists of isolated [SiO₆] octahedra and [Si₂O₇] groups which are linked by [PO₄] tetrahedra forming a three-dimensional network. The average interatomic distances are: Si[6]?O=1.76₈, Si[4]?O=1.60₇ and P?O=1.52_i Å. The compound is isotypic with Ge₅O[PO₄]₆.     

Extraction of Ternary Alloys: Synthesis and Crystal Structure of [K([2.2.2]crypt)]Cs7[Sn9]2(en)3

The compound [K([2.2.2]crypt)]Cs₇[Sn₉]₂(en)₃ ( 1 ) was synthesized from an alloy of formal composition KCs₂Sn₉ by dissolving in ethylenediamine (en) followed by the addition of [2.2.2]crypt and toluene. 1 crystallizes in the orthorhombic space group Pcca with a = 45.38(2), b = 9.092(4), c = 18.459(8) Å, and Z = 4. The structure consists of Cs₇[Sn₉]₂ layers which contain [Sn₉]^4– anions and Cs⁺ cations. The layers are separated by [K([2.2.2]crypt)]⁺ units. In the intermetallic slab (Cs₇[Sn₉]₂)^– compares the arrangement of pairs of symmetry‐related [Sn₉]^4– anions with the dimer ([Ge₉]–[Ge₉])^6– in [K([2.2.2]crypt)]₂Cs₄([Ge₉]–[Ge₉]), in which the clusters are linked by a cluster‐exo bond. The shortest distance between atoms of such two clusters in 1 is 4.762 Å, e. g. there are no exo Sn‐Sn bonds. The [Sn₉]^4– anion has almost perfect C_4v‐symmetry.     

Die Kristallstruktur des Lithiumheptagermanats Li2[Ge7O15]

Zusammenfassung Die Kristallstruktur der Verbindung Li₂[Ge₇O₁₅] wird mit Hilfe dreidimensionaler Patterson- und Fourier-Synthesen bestimmt und nach der Methode der kleinsten Quadrate verfeinert. Die Gitterparameter der orthorhombischen Elementarzelle (Pbcn — D _2h ¹⁴ ) betragen:a=7,36,b=16,76 undc=9,69 Å. Die Struktur enthält stark gewellte Schichten aus [GeO₄]-Tetraedern, die über [GeO₆]-Oktaeder zu einem dreidimensionalen Gerüst verknüpft sind; sie läßt sich durch die Formel Li₂[Ge(Ge₂O₅)₃] charakterisieren. Als mittlere Ge–O-Abstände werden erhalten: 1,735 Å (K.Z. 4) und 1,893 Å (K.Z. 6).

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The crystal structure of Li₂[Ge₇O₁₅]

The crystal structure of Li₂[Ge₇O₁₅] has been determined by means of three-dimensional Patterson and electron density syntheses, and refined by least-squares method. The lattice parameters of the orthorhombic unit cell (Pbcn-D _2h ¹⁴ ) are:a=7.36,b=16.76 andc=9.69 Å. The crystal structure contains strongly puckered layers of [GeO₄]-tetrahedra linked by [GeO₆]-octahedra to form a three-dimensional framework; the structure can be characterized by the formula Li₂[Ge(Ge₂O₅)₃]. The averaged Ge–O-distances are found to be: 1.735 Å (c. n. 4) and 1.893 Å (c.n. 6).

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Mit 1 Abbildung     

Sm4S3[Si2O7] und NaSm9S2[SiO4]6: Zwei Sulfidsilicate mit dreiwertigem Samarium

Sm₄S₃[Si₂O₇] and NaSm₉S₂[SiO₄]₆: Two Sulfide Silicates with Trivalent Samarium The sulfide silicates Sm₄S₃[Si₂O₇] and NaSm₉S₂[SiO₄]₆ are obtained as light yellow transparent crystals by the reaction of Sm, Sm₂O₃, S, and SiO₂ with fluxing SmCl₃ or NaCl, respectively, in suitable molar ratios in fused evacuated silica tubes (850 °C, 7 d). Tetragonal crystals of Sm₄S₃[Si₂O₇] (I4₁/amd; Z = 8; a = 1186.4(1); c = 1387.0(2) pm) with ecliptically conformed [Si₂O₇]^6–‐groups of corner sharing [SiO₄]‐tetrahedra are formed. These double tetrahedra as well the sulfide anions (S^2–) coordinate two crystallographically independent metal cations. They provide coordination numbers of 8 + 1 (5 S^2– and 3 + 1 O^2–) for Sm1 and 9 (3 S^2– and 6 O^2–) for Sm2. NaSm₉S₂[SiO₄]₆ crystallizes hexagonally (P6₃/m; Z = 1; a = 975.32(9); c = 676.46(7) pm) in a modified bromapatite‐type structure. The coordination spheres about the two crystallographically different Sm³⁺ cations are built up by oxygen atoms of the orthosilicate units ([SiO₄]^4–) and sulfide anions (S^2–). As a result, Sm1 and Sm2 have coordination numbers of 9 and 8, respectively. Na⁺ and (Sm1)³⁺ occupy the position 4 f in a molar ratio of 1 : 3 whereas the lower coordinated (Sm2)³⁺ occupies the 6 h position.     

Potassium oxoaluminate ­antimonate(III), K2[Al2Sb2O7]

Dipotassium dialuminium diantimonate, K₂[Al₂Sb₂O₇], crystallizes in the trigonal space group . The structure is isotypic with K₂Pb₂Ge₂O₇ and consists of [Al₂Sb₂O₇]^2? layers containing Al³⁺ in a nearly regular tetrahedral and Sb³⁺ in a Ψ‐tetrahedral environment of O ligands.     

[Ge2S5(S2)]4−, A NLO-Active Unit Leading to an Asymmetric Structure Discovered in Li2Cs4Ge2S5(S2)Cl2: An Experimental and Theoretical study

Metal-centered MS₄ tetrahedra are fundamentally important building blocks for the structural construction of infrared (IR) nonlinear optical (NLO) mateirals, because they have a large effect on properties like second-harmonic generation, birefringence, band gap, etc. Therefore, rational design and selection of these tetrahedra could effectively help synthesize new materials and give satisfactory properties. In this work, we reported a new NLO-active [Ge₂S₅(S₂)]⁴⁻ unit composed of two corner-shared GeS₄ tetrahedra with a nonpolar covalent S−S bond, discovered in a new compound of Li₂Cs₄Ge₂S₅(S₂)Cl₂. To the best of our knowledge, this [Ge₂S₅(S₂)]⁴⁻ unit has never been discovered. [Ge₂S₅(S₂)]⁴⁻ units have intrinsic asymmetric features and lead to the whole structure being noncentrosymmetric (NCS). Further, real-space atom-cutting methods reveal that they make almost all the contribution to the second-harmonic generation response (SHG) for Li₂Cs₄Ge₂S₅(S₂)Cl₂. All of the above indicate that the [Ge₂S₅(S₂)]⁴⁻ unit is a new functional unit and a good choice for designing new IR NLO materials.     

Two caesium vanadium hydrogenphosphates with tunnelled structures: Cs2V2O3(PO4)(HPO4) and Cs2[(VO)3(HPO4)4(H2O)]·H2O

Dicaesium divanadium trioxide phosphate hydrogenphosphate, Cs₂V₂O₃(PO₄)(HPO₄), (I), and dicaesium tris[oxidovanadate(IV)] hydrogenphosphate dihydrate, Cs₂[(VO)₃(HPO₄)₄(H₂O)]·H₂O, (II), crystallize in the monoclinic system with all atoms in general positions. The structures of the two compounds are built up from VO₆ octahedra and PO₄ tetrahedra. In (I), infinite chains of corner‐sharing VO₆ octahedra are connected to V₂O₁₀ dimers by phosphate and hydrogenphosphate groups, while in (II) three vanadium octahedra share vertices leading to V₃O₁₅(H₂O) trimers separated by hydrogenphosphate groups. Both structures show three‐dimensional frameworks with tunnels in which Cs⁺ cations are located.