Zur Darstellung und Struktur von LaNb5O14

Preparation and Structure of LaNb₅O₁₄ Single crystals of LaNb₅O₁₄ could be prepared by chemical transport reactions (T₂ → T₁; T₂ = 1050°C; T₁ = 950°C) using chlorine as transport agent. LaNb₅O₁₄ crystallizes in the orthorhombic space group Pbem with cell dimensions a = 3.8749(2) Å; b = 12.4407(6) Å and c = 20.2051(9) Å; Z = 4; R = 6.28%, R_w = 3.74%. The structure consists of two types of Nb? O-polyhedra. Especially remarkable are chains of edge-sharing pentagonal NbO₇-bipyramids, which are interconnected by corner-sharing NbO₆-octahedra. Tunnels running in a-direction are created by this framework of NbO₆- and NbO₇-polyhedra. Lanthanum atoms are located in these tunnels at levels inbetween the niobium atoms. The relationship to O? LaTa₃O₉ and M? CeTa₃O₉ type structures will be discussed.     

Zur Darstellung und Struktur von M1?LnTa3O9 (Ln = Pr,Nd) Röntgenographische und elektronenmikroskopische Untersuchungen

Preparation and Structure of M1? LnTa₃O₉ (Ln = Pr, Nd), X-Ray and Electronmicroscopical Investigations New ternary compounds M1? LnTa₃O₉ (Ln = Pr, Nd) could be prepared by chemical transport reaction in a temperature gradient T₂ → T₁ (T₂ = 1100°C; T₁ = 1000°C; CI₂ as transport agent). M1 NdTa₃O₉ crystallizes in the monoclinic space group P 2₁/m with a = 5.3840(9) Å, b = 7.550(1) Å, c = 8.1911(9) Å and β = 92.46(1)°. The structure was refined to give R = 6.29% and R_w = 6.20%. It is built of double and single chains of corner-sharing TaO₆ octahedra extended along the b-axis. Tunnels running along [010] are created by the framework of TaO₆ octahedra. Ln (Ln = Pr, Nd) is located in these tunnels to levels of y = 1/4 and 3/4. A structure refinement for isostructural M1? PrTa₃O₉ led to a = 5.4051(7) Å, b = 7.5680(2) Å, c = 8.1964(9) Å, β = 92.38(2)° and R = 7.72%, R_w = 7.57%. By grinding in an agate mortar M1? LnTa₃O₉ transforms into M2? LnTa₃O₉, a new modification with a higher density. High resolution transmission electron microscopy images of the M1? PrTa₃O₉ structure were made along the [010] direction. They could be interpreted by comparing them with images calculated on the basis of the multi-slice method.     

Tribochemische und thermische Umwandlungen von LnTa3O9 (Ln = Pr,Nd) – röntgenographische und elektronenmikroskopische Untersuchungen

Tribochemical and Thermal Transitions of LnTa₃O₉ (Ln = Pr, Nd) — X-ray and Electron Microscopic Investigations Upon grinding crystals of M1? LnTa₃O₉ (Ln = Pr, Nd) [3] undergo a tribochemical phase transition. This leads to a new modifikation M2? LnTa₃O₉ with a significant higher density. We tried to find out more about the structure with high resolution electron microscopic investigations. According to electron diffraction and powder patterns the lattice parameters are (CuKα₁, λ = 1,54051 Å): M2? PrTa₃O₉: a = 6.2545(7) Å, b = 7.6736(7) Å, c = 6.5316(8) Å, β = 93.93(9)°; M2? NdTa₃O₉: a = 6.2552(5) Å, b = 7.6598(7) Å, c = 6.5103(4) Å, β = 94.096(7)°; (Z = 2). Using the intensities of powder patterns two structure models were calculated (space group P2₁/m, P2/m; R < 20%, heavy metal positions only). A through focus series of high resolution images was in better agreement with the first model (space group P2₁/m). Both models show a remarkable similarity to the structure of M? CeTa₃O₉ [4]. A thermal phase transition leads to M? PrTa₃O₉ and M? NdTa₃O₉ which are both isostructural to M? CeTa₃O₉.     

Zur Darstellung und Struktur von LaTa3O9 Röntgenographische und elektronenmikroskopische Untersuchungen

Preparation and Structure of LaTa₃O₉. X-Ray and Electronmicroscopic Investigations In the system La₂O₃/Ta₂O₅ a new ternary compound LaTa₃O₉ could be prepared by chemical transport in a temperature gradient T₂ → T₁ (1100 → 1040°C; Cl₂ was added). LaTa₃O₉ is orthorhombic, space group Pnma–D with the lattice constants a = 6.59₅, b = 7.66₄, and c = 12.48₁ Å. In the structure ribbons of pentagonal TaO₇-bipyramids are recognizable parallel to the a-direction. These ribbons are connected with each other in the (010) plane by TaO₆-octahedra. The tunnels formed in this way are occupied by La atoms. High resolution transmission electron microscopy images of the structure were made along the [010] direction. They were interpreted by using images calculated on the basis of the multi-slice method.     

Zur Darstellung und Struktur von LaTa7O19 Röntgenographische und elektronenmikroskopische Untersuchungen

Preparation and Structure of LaTa₇O₁₉. X-Ray and Electronmicroscopic Investigations In the system La₂O₃/Ta₂O₅ a new ternary compound LaTa₇O₁₉ could be prepared by chemical transport in a temperature gradient T₂ → T₁ (1120 → 1020°C; Cl₂ was added). LaTa₇O₁₉ is hexagonal, space group P6 with the lattice constants a = 6.23₆ and c = 19.99₅ Å. In the structure double layers of pentagonal TaO₇-bipyramids are recognizable perpendicular to [001]-direction. They alternate with a single layer consisting of La? O and Ta? O coordination polyhedra. Images of the structure were made with high resolution transmission electron microscopy along the [001]-direction. Despite the length of the axis the computer simulation based on the multi-slice method agreed well with the experimental images.     

Structure of the copper(I) tantalum oxide,Cu5Ta11O30

The structure of hexagonal Cu₅Ta₁₁O₃₀ (space group $\text{P}\text{6}\text{2c}$) has been determined from single-crystal diffractometer data. The cell dimensions are a = 6.2297(2) Å and c = 32.550(2) Å, and the cell content is two formula units. The structure is related to those of CaTa₄O₁₁ and CeTa₇O₁₉ and contains alternately single and double layers of TaO₇ pentagonal bipyramids sharing edges in the equatorial plane in the same way as UO₇ in α-U₃O₈. The layers are connected by TaO₆ octahedra and linear CuO₂ groups, both formed by the apex oxygens of the TaO₇ bipyramids. Refinement was made with the least-squares technique using 729 reflections, of which 422 were independent. The conventional R value was 3.9%.     

Neues zu Oxidchloriden der Seltenen Erden mit Vanadium und Rhenium

New Oxychlorides of the Rare-Earth Metals with Vanadium and Rhenium i) New compounds Ln_12.33V₆O₂₃(OH)Cl₂₀ (Ln = La, Ce) were prepared by heating mixtures of LnCl₃, LnOCl and V₂O₅ (4 : 8 : 3) in evacuated, sealed silica ampoules (850 °C, 4 d). Single crystals could be obtained by chemical vapor transport (T₂ → T₁, T₂ = 900 °C, T₁ = 800 °C, 14 d, p(Cl₂, 298 K) ≈ 70 mbar). The single-crystal study of the lanthanum compound [a = 17.8818(25) Å, c = 4.0567(7) Å, Z = 1, 1035 independent I₀, 70 parameters, R1 = 3.52%] showed that vanadium has CN = 4 (tetrahedrally) and lanthanum has CN = 9 (threefold capped trigonal prismatic). A strong relationship to the structures of the Pr₃NbO₄Cl₆- and the La₂TaO₄Cl₃-type could be discussed. ii) Further we obtained dark red powder of La₃ReO₆Cl₃ by heating (740 °C, 5 d) a mixture of ReO₃ and LaOCl (1 : 3) in sealed silica ampoules under argon atmosphere (p{Ar, 298 K} = 1 atm). This new rhenium-compound crystallizes in the hexagonal space group P6₃/m (No. 176) [a = 9.4164(6) Å, c = 5.4248(4) Å] and is isostructural to La₃WO₆Cl₃.     

Zur Kenntnis ‘Kationen-reicher’ Tantalate Über Li7[TaO6]

On Tantalates ‘rich in Cations’ On Li₇[TaO₆] For the first time, colourless single crystals of Li₇[TaO₆] were grown by annealing intimate mixtures of Li₂O and Ta₂O₅ (Li:Ta = 7,7:1) in closed Ni-cylinders (1 000°C, 156 d). [Trigonal-rhomboedral with a = 535.8(1) pm, c = 1 507.3(3) pm, c/a = 2.81/Guinier-Simon-powder data; Z = 3. Space group R3 for the part Li(1)₆TaO₆ and presumably P3 for Li₇TaO₆, including Li(2)]. The crystal structure was solved by four-cycle-diffractometer data [Mo? Kα , 331 from 331 I_o(hkl), R = 1.99%, R_w = 1.96%], parameters see text. The positions of anions correspond to the motif of a hexagonal closest packing of spheres, obviously deformed (with MEFIR of O^2? space filling corresponds to 69.8% instead of expected 73.2%. 1/3 of the octahedron holes are ordered occupied by Ta and Li(2), 1/2 of the tetrahedral holes likewise ordered by Li(1). All polyhedra of coordination of the anions are trigonal prisms. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these calculated via Mean Fictive Ionic Radii, as well as charge distribution ‘CHARDI’ are calculated and discussed.     

Zum chemischen Transport von Verbindungen des Typs LnTa7O19 (Ln = La?Nd) mit einer Bemerkung zur Strukturverfeinerung von NdTa7O19

Chemical Transport Reactions of Compounds LnTa₇O₁₉ (Ln = La? Nd) and Structure Refinement of NdTa₇O₁₉ Crystals of compounds LnTa₇O₁₉ (Ln ? Na? Nd) could be obtained by chemical transport reactions (T₂ → T₁; T₂ = 1100°C, T₁ = 1000°C) using chlorine (p(Cl₂; 298 K) = 1 atm) as transport agent. An increase of transport rate and an improvement of crystal growth was observed if small amounts of vanadium metal were added. Solid state reactions with mixtures of Ln₂O₃/Ta₂O₅ (1:7) in air (T ≈ 1400–1500°C), however, were not succesful because the resulting samples contained LnTa₇O₁₉ with other ternary phases as by-products. NdTa₇O₁₉ crystallizes in the well-known LaTa₇O₁₉-type structure with cell dimensions of a = 6.2229(3) Å, c = 19.939(2) Å and Z = 2. The crystal structure was refined in space groups P6 c2 (R = 3.35%, R_W = 2.67%) and P6₃/mcm (R = 4.75%, R_W = 3.88%). Taking aspects of structural chemistry, x-ray results and MAPLE calculations into account, however, the spacegroup P6 c2 should be preferred.     

Ein neues Praseodymniobat Pr2Nb11O30

A New Praseodymiumniobate Pr₂Nb₁₁O₃₀ By chemical vapor transport (T₂ → T₁, T₂ = 950 °C, T₁ = 900 °C, 3 d) of a mixture of PrOCl and Nb₂O₅ (1 : 1) using 5 mg NH₄Cl as transport agent we obtained the new compound Pr₂Nb₁₁O₃₀. The crystal structure determination [a = 6.2325(5) Å, c = 32.3677(36) Å, Z = 2, 1631 independent I₀, 69 parameters, R1 = 2.07%] shows CN = 8 (twofold capped octahedrally) for Pr, CN = 7 (pentagonal bipyramidally) for Nb(1,2) and CN = 6 (octahedrally) for Nb(3). The structure is closely related to that of Cu₅Ta₁₁O₃₀.     

Elektronenmikroskopische Untersuchung der Realstruktur von O?LaTa3O9, M?CeTa3O9 und M2?PrTa3O9 – Nachweis einer neuen M1?CeTa3O9-Modifikation

Electronmicroscopic Investigations on Disordered Crystals of O? LaTa₃O₉, M? CeTa₃O₉, and M2? PrTa₃O₉ – Proof of a New M1? CeTa₃O₉-Modification High resolution electron microscope investigations on O? LaTa₃O₉ and M2? PrTa₃O₉ showed twinned areas in both cases. With the help of electron microscopic pictures and models of the crystal structures, respectively, we obtained informations about the structural imperfections. Furthermore we present images of thin crystals which contain areas of two different modifications M1? PrTa₃O₉ and M2? PrTa₃O₉. By comparing these images with the corresponding computed contrasts we obtained a structure model of the phase boundary. Investigations on crystals of M? CeTa₃O₉ showed small areas of a new modification M1? CeTa₃O₉ which is isotypic to M1? LnTa₃O₉ (Ln=Pr, Nd) according to electron diffraction and high resolution images.     

Nd4Ti9O24: Präparation und Struktur

Preparation and Crystal Structure of Nd₄Ti₉O₂₄ The compound Nd₄Ti₉O₂₄ was prepared by heating mixtures of Nd₂O₃/TiO₂ (1 : 4.5) at temperatures of T = 1 330°C in air (2× 1d). Single crystals of Nd₄Ti₉O₂₄ were obtained by chemical transport reaction (T₂→T₁; T₁ = 1000°C, T₁ = 900°C, 14 d) using chlorine (p(Cl₂, 298 K) = 1 atm) as transport agent with Nd₄Ti₉O₂₄ as starting material. Nd₄Ti₉O₂₄ crystallizes in the orthorhombic space group Fddd (No. 70) with a = 13.9926(11) Å, b = 35.2844(21) Å, c = 14.4676(17) Å (Z = 16). The structure was refined to give R = 4.0% and R, = 3.7%. Main building units are TiO₆ octahedra, NdO₆ distorted square antiprisms and NdO₆ octahedra.     

Zur Kenntnis von RbTaO3 – ein neuer Typ einer Schichtstruktur

On the Knowledge of RbTaO₃ – a New Type of a Layer Structure RbTaO₃ crystallizes monoclinic with a = 9.58₉, b = 8.50₅, c = 8.13₅ Å, β = 94.8₇°, Z = 8, space group C2/m. The crystal structure (Fourcircle-diffractometer data, 4° ≤ Θ ≤ 33°, 1014 hkl, MoKα, R = 9,9%) shows sheets [TaO₃] connected by Rb; one half of Ta is surrounded by O octahedrally, the other part tetragonal-pyramidal. Effective Coordination Numbers, ECoN, and the Madelung Part of Lattice Energy, MAPLE, have been calculated and are discussed.     

Structure and thermal decomposition of Cs<Subscript>2</Subscript>HPO<Subscript>4</Subscript> · 2H<Subscript>2</Subscript>O

The thermal transformations of disubstituted cesium orthophosphate crystal hydrate under heating in air up to 400°C have been studied. The dehydration process occurs in two stages with the loss of 0.6 water molecules at 60?100°C and 1.4 water molecules at 100?160°C. Anhydrous Cs₂HPO₄ is stable up to 300°C and is completely converted into cesium pyrophosphate Cs₄P₂O₇ at 330°C. The structure of Cs₂HPO₄ · 2H₂O has been determined. The compound crystallizes in monoclinic space group P2₁/c and has the unit cell parameters a = 7.4761(5) Å, b = 14.2125(8) Å, c = 7.9603(6) Å, β = 116.914(5)°, V = 754.20(9) ų, and Z = 4 at?123°C. An earlier unknown polymorph of Cs₄P₂O₇ has been found. According to X-ray powder diffraction data, hexagonal space group Р6₃ has been proposed for the formed pyrophosphate.     

Synthese,Kristallstruktur und thermische Entwässerung von CsMnF4 · 2H2O

Synthesis, crystal structure and thermal dehydration of CsMnF₄ · 2H₂O The preparation of a new fluoromanganate (III)-complex CsMnF₄ · 2H₂O is reported. It crystallizes in the monoclinic space group C2 with a = 11.891(2) Å, b = 6.589(1) Å, c = 10.558(1) Å, β = 131.46(1)° and Z = 4. The crystal structure has been solved from diffractometer data by heavy-atom methods and refined to a conventional R-value of 1.8% (including the contributions of three hydrogen atoms in measured and one in calculated positions). The structure is characterized by isolated, tetragonally distorted [MnF₄(OH₂)₂]-octahedra with Mn-F-distances from 1.801(8) Å to 1.870(7) Å and Mn-O-distances of 2.146(6) Å and 2.268(6) Å. Cesium exhibits an irregular 10-coordination by 8 F-atoms and 2 O-atoms (mean values for the two independent cesium ions: Cs-F = 3.17 Å and 3.21 Å, Cs-O = 3.32 Å and 3.29 Å). The [MnF₄(OH₂)₂]-octahedra are connected to six neighbouring octahedra by hydrogen bonding. The dehydration of the complex has been studied by thermoanalytical methods and power x-ray-diffractometry. The unit cell of the dehydrated compound, CsMnF₄, is tetragonal with a = 7.936(1) Å and c = 6.341(1) Å. A close relationship to the structure of CsFeF₄, which is a superstructure variant of the T1A1F₄-type[6], is indicated by the similarity of the corresponding unit cells and preliminary structure factor calculations. A proposition for the crystal structure of CsMnF₄ is developed on the basis of (2 + 2 + 2)-orthorhombic distorted MnF₆-octahedra.     

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.     

Structure Cristalline du Trimétaphosphate d'Indium(III)

Crystal Structure of In (PO₃)₃ Indium(III) trimetaphosphate In(PO₃)₃ crystallizes in the monoclinic space group Ic with a = 10.876(2) Å, b = 19.581(2) Å, c = 9.658(2) Å, β = 97.77(1)° and Z = 12. The structure was refined to R = 0.027 utilizing 1171 independent reflections. The structure consists of infinite chains of [PO₄] tetrahedra sharing corners with each other. InO₆ octahedra connect parallel chains. Each oxygen atom is shared between two [PO₄] tetrahedra (in the infinite chains (PO₃)_n) or one [PO₄] tetrahedron and one [InO₆] octahedron. For the first type of oxygen atoms (O_M) the P? O distances are about 0.1 Å greater than the P? O distances of the second type of oxygen atoms (O_m). The [InO₆] groups are moderately distorted and the average In? O bond length for the three In³⁺ ions is 2.117 Å.     

Darstellung und Struktur von Ln3TiO4Cl5(Ln = La − Nd) - die ersten Oxochlorotitanate der Seltenen Erden

Preparation and Crystal Structure of Ln₃TiO₄Cl₅ (Ln = La?Nd) – the First Oxochlortitanates of Rare Earth The compounds Ln₃TiO₄Cl₅ have been prepared by reaction of LnCl₃/LnOCl/TiO₂ (1:2:1) (Ln = La?Nd) in evacuated silica ampoules. Single crystals of La₃TiO₄Cl₅ were obtained by chemical transport reaction (T₂ → T₁; T₂ = 1050°C, T₁ = 950°C) using chlorine (p(Cl₂; 298 K) = 1 atm) and sulfur as transport agents with La₂TiO₅ as starting material. La₃TiO₄Cl₅ crystallizes in the orthorhombic space group Pnma (No. 62) with cell-dimensions a = 16.760(2) Å, b = 4.0991(6) Å, c = 14.634(2) Å, Z = 4. The structure was refined to give R = 4.76%, R_w = 2.47%. Main building units are TiO₅ trigonal bipyramides and threefold capped trigonal prisms around La. The relationship to La₂TaO₄Cl₃ will be discussed.     

Zum System Zn/Mo/O. I. Phasenbestand und Eigenschaften der ternären Zinkmolybdate; Struktur von Zn3Mo2O9

On the System Zn/Mo/O. I. Phases and Properties of Ternary Zinc Molybdates; Crystal Structure of Zn₃Mo₂O₉ Several ternary compounds are known in the Zn/Mo/O-system. The phases ZnMoO₄, Zn₂Mo₃O₈ and Zn₃Mo₂O₉ are stable at 900°C. The coexistence ranges are shown in the ternary phase diagram. The structure of Zn₃Mo₂O₉ has been determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/m (a = 7,757(1) Å, b = 7,132(1) Å, c = 8,370(2) Å, β = 117,40(1)º, Z = 2).     

N‐Propionylhydroxylamine forms a three‐dimensional hydrogen‐bonded framework structure

The title compound, N‐hydroxy­propan­amide, C₃H₇NO₂, crystallizes with Z′ = 3 in P2₁/c. The mol­ecules are linked by three N—H?O hydrogen bonds [N?O 2.8012 (16) to 2.8958 (15) Å; N—H?O 163 to 168°] and by three O—H?O hydrogen bonds [O?O 2.6589 (15) to 2.6775 (17) Å; O—H?O 165 to 177°] into a single three‐dimensional framework.