Zur Frage nach der Existenz eines kubischen Pyrochlors Pb2Sb2O7

On the Problem of the Existence of a Cubic Pyrochlore Pb₂Sb₂O₇ The reaction of PbO, PbO₂, PbCO₃ or Pb(CH₃CO₂)₂ · 3 H₂O with Sb₂O₃ (ratio 2:1 Mol.) gives up to 700°C a cubic pyrochlore together with PbSb₂O₆. The pyrochlore contains Pb(IV) and has the approximate composition Pb[PbSb]O_6,75 with a = 1066–1069 pm. After heating up to 900°C rhombohedral Pb₂Sb₂O₇ is formed. There is no evidence for the existence of a cubic Pb₂Sb₂O₇ with Pyrochlore structure.     

High-pressure behaviour of synthetic weberite-type Mn2+2Sb5+2O7: An in situ single-crystal X-ray study

An in situ high-pressure X-ray diffraction study has been carried out at room temperature up to 9.26 GPa on synthetic Mn₂Sb₂O₇ having a weberite-3T structure. A 2nd-order Birch–Murnaghan Equation of State (EoS) was used to refine the pressure–volume data. The refinement of the unit-cell volume and of the isothermal bulk modulus at room pressure leads to: V₀ = 782.7(2), K_T0 = 150(1) GPa. Unit-cell parameters decrease gradually as a function of pressure with a bulk modulus anisotropy scheme, with a being the softest direction. The overall mean polyhedral distances are quite constant, indicating a scarce compressibility of both the A and B polyhedra in the pressure range investigated. The compressional behaviour of Mn₂Sb₂O₇ is compared with that shown by ingersonite, Ca₃MnSb₄O₁₄, and synthetic orthorhombic Ca₂Sb₂O₇.     

Synthesis and crystal structure of a new cesium barium borate,CsBaB3O6

A new ternary borate oxide, cesium barium borate, CsBaB₃O₆, has been synthesized by solid-state reaction at 700 °C, and the single crystals were grown using CsF as a flux. The crystal structure has been determined by X-ray diffraction. It crystallizes in the trigonal space group P321 with a cell of dimensions a=12.469(3)Å, c=7.444(3)Å, α=90.00°, γ=120.00°, V=1002.3(5)ų, Z=6. The fundamental building units of CsBaB₃O₆ are the B₃O₆ plane hexagonal rings, which are parallel to each other and stack along the c-axis, and the Cs and Ba atoms alternately occupy sites between the B₃O₆ sheets. A comparison of the structures of CsBaB₃O₆, β-BaB₂O₄ and CsBO₂ is presented.     

Synthesis and solid state studies on Mb2Sb2O7 and (Mn1−xCdx)2Sb2O7 pyrochlores

Pyrochlore oxides of the type Mn₂Sb₂O₇ and (Mn_1?xCd_x)₂Sb₂O₇ have been synthesized by high-temperature solid state reactions and characterized by X-ray diffraction and chemical analysis. X-Ray diffraction studies showed that the compound Mn₂Sb₂O₇ has a rhombohedrally distorted pyrochlore structure. In the solid solutions (Mn_1?xCd_x)₂Sb₂O₇, the phases with x ≥ 0.6 are cubic. Magnetic and ¹²¹Sb Mössbauer studies indicate that all the Mn and Sb are present in the +2 and +5 state occupying A and B sites, respectively, in the pyrochlore structure. Electrical measurements indicate that the compounds are insulators or semiconductors exhibiting p-type behavior. The stoichiometry and probable cause of the rhombohedral distortion in Mn₂Sb₂O₇ and solid solutions are discussed.     

A Coordination Polymer based on Interconnection of Thioantimonate(III) and [Mn(terpy)]2+ Complexes: Synthesis,Crystal Structure,and Properties of {[(Mn(terpy))2Sb4S8]·0.5H2O}n

Applying Schlippe's salt, Na₃SbS₄ · 9H₂O, in the presence of the in-situ formed [Mn(terpy)]²⁺ complex (terpy = 2,2':6',2''-terpyridine) the new compound {[(Mn(terpy))₂Sb₄S₈] · 0.5H₂O}_n ( I ) could be obtained under solvothermal conditions. Interestingly, in the crystal structure the two unique Mn²⁺ cations adopt different environments to form a MnN₃S₃ octahedron and a MnN₃S₂ trigonal pyramid. The trigonal pyramidal SbS₃^3– anions share common edges yielding a Sb₈S₈ ring. Covalent bonds between Mn²⁺ and S^2– generate MnSb₂S₃ and Mn₂Sb₄S₆ heterocycles. The Sb₈S₈ and Mn₂Sb₄S₆ rings are condensed to form a chain. The MnN₃S₃ octahedron and the MnN₃S₂ polyhedron share a common S^2– anion and antiferromagnetic properties are observed mediated by superexchange interactions. {[(Mn(terpy))₂Sb₄S₈] · 0.5H₂O}_n shows luminescence in the blue-green spectral range, assigned to combined contributions from Mn²⁺ ions and from the organic ligand.     

Crystal structure of a new lithium indium borate Li3InB2O6

Single crystals of synthetic Li₃InB₂O₆ were obtained by heating a mixture of Li₂CO₃, In₂O₃ and B₂O₃; its formula was determined by the resolution of the structure from X-ray diffraction data. The compound is monoclinic, space group P2₁/n; the unit cell parameters are a=5.168(5) Å, b=8.899(9) Å, c=10.099(10) Å, β=91.112(17)°; Z=4. The crystal structure was solved from 669 reflections until R=0.0249; it exhibits a three-dimensional framework of vertex-sharing InO₅ trigonal bipyramids and BO₃ triangles, which isolates Li ions in channels. This structure is characterized by unusual oxygenated environments of In cations and of one of the three Li cations, which are forming more or less regular trigonal bipyramids. This compound melts incongruently at 827 °C; the powder may be obtained by annealing at 750 °C a mixture of Li₂CO₃, In₂O₃ and B₂O₃.     

Preparation and Crystal Structure of PbRe2O6. An Example of the Re2O10 Unit with No Metal-Metal Bonding

Single crystals of PbRe₂O₆ were obtained from a stoichiometric mixture of PbO and ReO₃ at 500°C. The structure was determined by Patterson methods from X-ray four-circle diffractometer data using 2 270 (392 unique) reflections; R_W(F) = 0.036. PbRe₂O₆ crystallizes in the trigonal space group R3m with a = 10.359(6) Å, c = 11.092(6) Å and Z = 9. The compound is isotypic with the trigonal modification of PbNb₂O₆ and contains an Re₂O₁₀ unit. Unlike other compounds containing this species, there is no metal-metal bonding.     

Synthesis and crystal structure of new sodium oxothiocyanofluoroantimonate(III) Na2Sb5F9O3(NCS)2

Na₂Sb₅F₉O₃(NCS)₂, a new complex, has been synthesized from NaSCN and SbF₃ aqueous solutions and studied by chemical, X-ray diffraction, and thermal analyses and IR, ^121,123Sb NQR, and ¹⁹F NMR spectroscopy. Its layered structure (triclinic symmetry system, a = 6.9998(1) Å, b = 9.4180(1) Å, c = 13.1094(2) Å, α = 74.815(1)°, β = 78.188(1)°, γ = 82.779(1)°, Z = 2, space group P $\bar 1$ ) is built of Na⁺ cations and [Sb₁₀F₁₈O₆(NCS)₄]^4? decanuclear complex anions that consist of two [Sb₅F₉O₃(NCS)₂]^2? pentanuclear complex anions linked by two weak Sb-F ionic bonds (2.529(2) Å). Decanuclear complex anions are linked into layers by secondary Sb…F bonds and Na-F bonds. Van der Waals interactions link these layers into a framework. The complex is stable up to 200°C.     

MnSb2O6-chitosan nanocomposite: An efficient catalyst for the synthesis of coumarins via Pechmann reaction

In this work, MnSb₂O₆-chitosan nanocomposites were synthesized and have been employed in Pechmann condensation for the synthesis of coumarin derivatives. MnSb₂O₆-chitosan nanocomposites were characterized by Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) techniques. The particles of MnSb₂O₆-chitosan have uniform spheres with sizes that are less than 100 nm. Simplicity, easy work-up, and short reaction times are advantages of this reaction. Also, we evaluated the antibacterial activity for some of the products, and the result showed significant pharmaceutical activities as antibacterial reagents against Staphylococcus aureus and Escherichia coli.     

Investigation of mixed divalent cation phosphates: synthesis and X-ray powder structure determination of CdBa2(P2O7)(HPO4)

Hydrothermal synthesis, characterization by X-ray diffraction, IR absorption, TGA and ab-initio crystal structure determination are reported for a new phosphate CdBa₂(P₂O₇)(HPO₄). It crystallizes in a monoclinic cell (space group Im, No. 8, Z=2) with a=11.9022(1) Å, b=5.5530(1) Å, c=7.3401(1) Å, β=90.091(1)°. The X-ray powder diffraction pattern was fitted by the Rietveld method technique with reliability R_Bragg=0.037. Hydrogen atoms could not be located. The crystal structure of CdBa₂(P₂O₇)(HPO₄) is built up from P₂O₇ diphosphate groups sharing four oxygen atoms with two CdO₆ trigonal prisms. Each CdO₆ trigonal prism shares one edge with the HPO₄ unit. Such an arrangement builds up isolated infinite chains CdP₃O₁₁ running along the b axis. Ba²⁺ ions are inserted between these chains in the (b,c) plane.     

Prototype structure of Pb5Ge3O11

The prototypic structure of the optically active ferroelectric Pb₅Ge₃O₁₁ has been deduced from packing considerations and refined from single-crystal diffractometer data. Interleaving segments of the apatite and nasonite structures in layers perpendicular to c gives the lead germanate structure. The space group of the prototype is $\text{P}\text{6}$, with a = 10.190, c = 10.624 Å, and Z = 3. Atomic coordinates were refined to give an R-factor of 0.093 using 463 X-ray reflections. The structure contains tetrahedral GeO₄ groups and double tetrahedral Ge₂O₇ groups in equal numbers. Lead is found in both trigonal pyramid and trigonal prism configurations.     

Synthesis and crystal structure of the novel Pb5Sb2MnO11 compound

The new Pb₅Sb₂MnO₁₁ compound was synthesized using a solid-state reaction in an evacuated sealed silica tube at 650°C. The crystal structure was determined ab initio using a combination of X-ray powder diffraction, electron diffraction and high-resolution electron microscopy (a=9.0660(8)Å, b=11.489(1)Å, c=10.9426(9)Å, S.G. Cmcm, R_I=0.045, R_P=0.059). The Pb₅Sb₂MnO₁₁ crystal structure represents a new structure type and it can be considered as quasi-one-dimensional, built up of chains running along the c-axis and consisting of alternating Mn⁺²O₇ capped trigonal prisms and Sb₂O₁₀ pairs of edge sharing Sb⁺⁵O₆ octahedra. The chains are joined together by Pb atoms located between the chains. The Pb⁺² cations have virtually identical coordination environments with a clear influence of the lone electron pair occupying one vertex of the PbO₅E octahedra. Electronic structure calculations and electron localization function distribution analysis were performed to define the nature of the structural peculiarities. Pb₅Sb₂MnO₁₁ exhibits paramagnetic behavior down to T=5 K with Weiss constant being nearly equal to zero that implies lack of cooperative magnetic interactions.     

Oxygen exchange properties in the new pyrochlore solid solution Ce2Sn2O7-Ce2Sn2O8

The phase-pure cerium stannate pyrochlore (Ce₂Sn₂O₇) has been prepared for the first time. The structure and oxidation states of both cations were carefully reviewed, and the compound was unambiguously replaced within the rare-earth stannate series. As a consequence of the low stability of trivalent cerium in oxide phases, one oxygen per formula unit could be intercalated by calcination under O₂ at 400 °C, leading to the new Ce₂Sn₂O₈ pyrochlore. This latter phase is subject to oxygen under-stoichiometry from 400 to 700 °C. However, oxygen deintercalation seems to be in competition with cerium oxide segregation at high temperature, leading to the formation of cerium deficient pyrochlore phases.     

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.     

Structure cristalline du phosphatoantimonate K3Sb3P2O14

K₃Sb₃P₂O₁₄ crystallizes in the rhombohedral system, space group $\text{R}\text{3}\text{m}$ with a = 7.147(1) Å, c = 30.936(6) Å, Z = 3. The structure was determined from 701 reflections collected on a Nonius CAD4 automatic diffractometer with $\text{Mo}\text{K}\text{α}$ radiation. The final R index and the weighted R_w index are 0.033 and 0.042, respectively. The structure is built up from layers of SbO₆ octahedra and PO₄ tetrahedra sharing corners. The potassium ions are situated between the (Sb₃P₂O₁₄)^3? covalent layers.     

Solid-state reactions in the system Cu—Sb—O; Formation of a new copper(I) antimony oxide

The solid-state reactions in the system Cu—Sb—O were investigated by thermogravimetry and X-ray diffraction. Equimolar mixtures of CuO and Sb₂O₃ form Cu(II)Sb₂O₆ when slowly heated in air up to 1000°C. The firt step in this reaction is the oxidation of Sb₂O₃ to Sb₂O₄ at 380–500°C, followed by further oxidation of Sb₂O₄ and the formation of CuSb₂O₆ at 500–1000°C. Thermal decomposition of CuSb₂O₆ in a flowing nitrogen atmosphere occurs in three stages; the first, with an activation energy of 356 kJ mole^?1, results in the formation of a new copper(I) antimony oxide, with a composition of Cu₄SbO_4.5, as determined by atomic absorption analysis and X-ray fluoresecence. Confirmation of predominantly monovalent copper and pentavalent antimony in the new compound was by ESR and ESCA, respectively. Two forms of Cu₄SbO_4.5 have been distinguished; one of these (form II) has a structure of lower symmetry, and decomposes when heated in air at 600°C to a mixture of CuO and another new copper antimony oxide, as yet uncharacterized. On further heating to 1100°C in air, Cu₄SbO_4.5 (form I) gradually reforms. Details of these reactions are summarized and X-ray powder data presented for Cu₄SbO_4.5.     

Synchrotron X‐ray study of ortho­rhombic Rb3Ta5O14 with a modified pyrochlore structure

The structure of a new orthorhombic trirubidium pentatantalum oxide (Rb₃Ta₅O₁₄) phase with Pnma symmetry was identified from a half sphere of synchrotron X‐ray data measured at a wavelength of 0.85 Å. This notionally linked TaO₆ octahedral structure broadly consists of three different modifications of the pyrochlore ring motif with layer stacking normal to (205) planes. Successive pyrochlore layers do not simply stack normal to these planes but are offset along the [100] axis. An unusual aspect of this structure is the occurrence of TaO₅ trigonal bipyramids in structurally complex regions where the modified pyrochlore rings connect.     

Untersuchung der Phasengleichgewichte in den Systemen Sb2O3?SO3?H2O und Bi2O3?SO3?H2O

Investigation of Phase Equilibria in the Systems Sb₂O₃? SO₃? H₂O and Bi₂O₃? SO₃? H₂O Phase equilibria in the systems Sb₂O₃? SO₃? H₂O and Bi₂O₃? SO₃? H₂O within the concentration range of 1 up to 98.5% H₂SO₄ at 100°C are studied. In the system Sb₂O₃? SO₃? H₂O crystallization fields of five compounds depending on the H₂SO₄ concentration were determined: 5Sb₂O₃ · Sb₂(SO₄)₃ · 3H₂O; 7Sb₂O₃ · 2Sb₂(SO₄)₃; 2Sb₂O₃ · Sb₂(SO₄)₃; Sb₂O₃ · Sb₂(SO₄)₃ and Sb₂(SO₄)₃. The obtained compounds are identified by chemical and derivatographic analysis.     

Kristallstruktur von Na5P3O10 · 6 H2O

Crystal Structure of Na₅P₃O₁₀ · 6 H₂O Na₅P₃O₁₀ · 6 H₂O crystallizes triclinic in P1 with a = 1 037.0(2), b = 984.8(4), c = 761.5(3) pm; α = 92.24(7)°, β = 94.55(9), γ = 90.87(6)°; Z = 2. The structure has been determined from fourcycle diffractometer data (2 089 independent reflections, R = 0.053). All hydrogen positions have been taken from a weighted difference-fourier-syntheses. Na₅P₃O₁₀ · 6 H₂O forms colorless, plate-like crystals, which are twinned systematically parallel (001) and can be divided mechanically into single-crystalline portions.