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.     

In‐situ Oxidation Products of Nb4W13O47: A High‐Resolution Transmission Electron Microscopy Study

Crystallites of Nb₄W₁₃O₄₇ were heated by a focussed electron beam in an oxygen atmosphere (p_O2 = 20 mbar) inside the gas reaction cell installed within the polepiece of a 400 kilovolt transmission electron microscope. The HRTEM investigation of the resulting oxidation products revealed the presence of structures which differ significantly from those generated by conventional oxidation in air. In a first reaction step, the arrangement of filled pentagonal tunnels in the tetragonal tungsten bronze (TTB) substructure became disordered, and small segregations of ReO₃‐type structure arose. Further treatment largely destroyed the original TTB‐type structure. In the residual bronze‐type structure, only a few TTB subcells were preserved while unusual structural arrangements, including hexagonal and heptagonal tunnels, were formed. Moreover, microdomains of a new intergrowth structure between the TTB type and the ReO₃ type occur. This structure comprises double pentagons of octahedra as well as slabs of diamond‐linked pentagonal columns. The oxygen excess in the oxidation product is structurally accommodated in large ReO₃‐type domains of tungsten oxide.     

High resolution electron microscopy studies of Ba4Nb14O23

The new compound, Ba₄Nb₁₄O₂₃, has been prepared by heating mixtures of Ba₅Nb₄O₁₅, Nb₂O₅ and Nb at 1 450°C under Ar. Ba₄Nb₁₄O₂₃ has been studied by means of high resolution electron microscopy and X-ray powder diffraction techniques. It has a C-centered orthorhombic unit cell with a=20.782(4), b=12.448(3), c=4.148(1) Å and Z=2. The structure of Ba₄Nb₁₄O₂₃ can be considered as being an intergrowth between BaNbO₃ and NbO. Characteristic building units are triple chains of corner sharing Nb₆ octahedra which are connected via columns of the perovskite type structure to a three dimensional network.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XLIV. Neue elektronenmikroskopische Untersuchung zur Realstruktur der metastabilen Nb2O5-Modifikation Ox1C

Contributions to the Investigation of Inorganic Non-Stoichiometric Compounds. XLIV. New Electron Microscopic Investigation of the Metastable Nb₂O₅ Modification Ox1C Oxidation of the blue-black NbO_x phases (2.4 < x < 2.5) in air or a diluted oxygen atmosphere leads all together to 21 metastable colourless (partly yellowish) Nb₂O₅ modifications. These can be described as compounds having block structures like the NbO_x phases themselves. At 200°C the oxidation process to the metastable phases proceeds quite slowly; at higher temperatures all polymorphs are finally transformed to H? Nb₂O₅. Electron diffraction patterns of the polymorph, which can be obtained by heating crystals of Nb₂₂O₅₄ in atmospheric environment at about 200°C (Ox1C), show extra spots in the c* direction compared to Nb₂₂O₅₄. This oxidation product is quite sensitive to the focused electron beam, so the reduction of the crystals back to Nb₂₂O₅₄ can only be avoided by reducing its intensity. Finally HRTEM images of thin crystal areas showing a superstructure were obtained. Comparing those characteristic image contrasts to calculated images of different point defect models one finds, that mainly one point defect is responsible for the superstructure. By migration of one Niobium atom two interstitial oxygen sites are created. So a structure model can be achieved leading to the formula Nb₄₄O₁₁₀.     

The Mixed Valence Tungsten(IV,V) Compound Na[W2O2Br6]

The reaction of W₆Br₁₂, NaBr, and WO₂Br₂ in the presence of Br₂ in a sealed silica tube yields Na[W₂O₂Br₆] together with WOBr₄ and WO₂Br₂ in the low temperature zone (temperature gradient 1030/870 K). Na[W₂O₂Br₆] crystallizes orthorhombically in the space group Immm (no. 71) with a = 3.775 Å, b = 10.400 Å, c = 13.005 Å and Z = 2. Pairs of condensed trans-[WO₂Br₄] octahedra with a common Br₂ edge form along [100] double chains [W₂O_4/2Br₆]^1– via the oxygen atoms. The mixed valent tungsten atoms are bonded to W₂ pairs with a 2 c–3 e bond (d(W–W) = 2.946 Å, d(W–O) = 1.888 Å, d(W–Br^b) = 2.537 Å, d(W–Br^t) = 2.535 Å, ∢O–W–O = 177.4°, ∢Br^b–W–Br^b (endocyclic) = 109.0°). The Na⁺ cations connect the anionic double chains to form two-dimensional layers parallel (001), which interact by van der Waals forces. The cations are eightfold coordinated by a cube of the terminal Br^t ligands of the polymeric anions (d(Na–Br) = 3.138 Å). Na[W₂O₂Br₆] may be discussed as an intercalation compound of the oxide bromide WOBr₃.     

Präparation und Charakterisierung von PbBr2·C4H10O3 (Diethylenglykol)

Structural Chemistry of PbBr₂·C₄H₁₀O₃ (Diethyleneglycol) Crystals of PbBr₂·C₄H₁₀O₃ have been synthesized and structurally characterized by single‐crystal X‐ray diffraction. PbBr₂·C₄H₁₀O₃ crystallizes monoclinic in space group P2₁/n (No. 14) with a = 9.370(1)Å, b = 10.045(1)Å, c = 21.090(1)Å, β = 98.98(1)° and Z = 8. The compound contains compact Pb—Br groups, which build colums parallel to [0 1 0] direction by Hydrogen Bonding.     

Zur Kenntnis der ionischen Ozonide P(CH3)4O3 und As(CH3)4O3

On the Knowledge of the New Ionic Ozonides P(CH₃)₄O₃ and As(CH₃)₄O₃ P(CH₃)₄O₃ and As(CH₃)₄O₃ were prepared via ion exchange in liquid ammonia and characterized by X-ray-powder, IR, MS and DTA techniques. P(CH₃)₄O₃ and As(CH₃)₄O₃ are isotypic and have a wurtzite-like arrangement of ions with rotationally disordered O₃^?. (Powder data: P6₃mc; P(CH₃)₄O₃: a = 687.8(2), c = 964.6(3) pm; As(CH₃)₄O₃: a = 708.6(1), c = 991.0(3) pm). As(CH₃)₄O₃ shows a displacive phase transition at ?135°C. The low temperature phase is orthorhombic (a = 715.8(7), b = 1 209(1), c = 943.3(1) pm).     

Preparation of VaM2−aO4 (M=Nb,Ta; 1>-a>-0.2) with different oxygen contents

This paper describes the thermal behaviour of various oxides of pentavalent V and Nb or Ta in different dynamic hydrogen atmospheres. Previous studies of the phases obtained by heating mixtures of V₂O₅ and M₂O₅ (M=Nb, Ta) in air lead to (i) preparation of VTaO₅ from both oxides for the first time, (ii) proof of the existence of the solid-solutions VM _m O_5/2(m+1), and (iii) proof that the materials described as NbVO₅ and β-TaVO₅ are really mixtures of VM₉O₂₅ and V₂O₅. Reduction of VMO₅ gives monophasic rutile-type VMO₄ from 650°C. Reduction VM₂O_7.5, V₃M₁₇O₅₀ and VM₉O₂₅ at 1000°C leads to monophase non-stoichiometric V_aM_2?aO_y only forM=Nb.     

Zur Kristallchemie der Kupfer-Lanthanoid-Oxowolframate: (I) triklin-α-CuTbW2O8, (II) monoklin-CuInW2O8 und (III) monoklin-CuYW2O8

The Crystal Chemistry of Copper Rare-Earth Oxotungstates: (I): triclinic-α-CuTbW₂O₈, (II): monoclinic-CuInW₂O₈ and (III): monoclinic-CuYW₂O₈ Single crystals of (I), (II) and (III) were prepared by recrystallisation in closed systems and examined by X-ray technique. (I): space group C? P1 , a = 7.3080, b = 7.8945, c = 7.1476 Å, α = 115.23, β = 116.21, γ = 56.98°, Z = 2; (II): space group C? C2/c, a = 9.6576, b = 11.6496, c = 4.9863 Å, β = 91.17°, Z = 4; (III): space group C? P2/n, a = 10.0504, b = 5.8214, c = 5.0224 Å, β = 94.23°, Z = 2. The crystal structures are discussed with respect to calculations of the coulombterms of lattice energy and possible valence states of Cu²⁺ and Mo⁵⁺.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XLIII. Darstellung und elektronenmikroskopische Untersuchung von (Cr,Nb)12O29

Contributions to the Investigation of Inorganic Non-Stoichiometric Compounds. XLIII. Preparation and Electron Microscopic Investigation of (Cr, Nb)₁₂O₂₉ Transport experiments in the system Cr/Nb/O yielded the compound (Cr, Nb)₁₂O₂₉ as crystalline green needles. The lattice parameters of the monoclinic cell are a = 31.162(8) Å, b = 3.8324(6) Å, c = 20.579(6) Å, β = 113.22(3)°. (Cr, Nb)₁₂O₂₉ is isotypic with monoclinic Nb₁₂O₂₉ as shown by Guinier diagrams and high resolution transmission electron microscopy. Characteristic structural building elements are [3 × 4]-blocks which are columnar sections from the ReO₃ structure. In the real structure one finds numerous defects. Under the influence of the electron beam we observed reversible changes of contrast which indicates that the positions of the M-particles (M = Cr, Nb) have shifted.     

ChemInform Abstract: Polyoxometalate Diphosphate Complexes. Folded Macrocyclic Dodecatungstates, ((O3PXPO3)4W12O36)16- (X: O,CH2).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Weitere Oxochlorotitanate LnTiO3Cl der Seltenen Erden (LnSm?Lu) - Präparation,Kristallstruktur, elektronenmikroskopische Untersuchung

New Rare Earth Oxochlorotitanates LnTiO₃Cl (Ln?Sm? Lu) - Preparation, Structure and Electron Microscopic Investigations After the preparation of SmTiO₃Cl we made the attempt to prepare analogous compounds with the heavier rare earth elements. We present 2 methods to prepare powders of LnTiO₃Cl (Ln = Sm? Lu) together with a new method to prepare the rare earth oxychlorides LnOCl (Ln = Tm? Lu). There will be also presented 2 methods to get single crystals of these compounds via chemical vapour transport. The new rare earth oxochlorotitanates LnTiO₃Cl (Ln = Eu? Lu) are isotypic to SmTiO₃Cl. They crystallize in the monoclinic space group: C2/m (No. 12). The lattice parameters (Å) are between a = 9.716(3), b = 3.942(2), c = 10.100(4) (SmTiO₃Cl) and a = 9.748(1), b = 3.8454(5), c = 9.625(2) (LuTiO₃Cl), Z = 4. We observed a permanent decay of the cell volume with the decay of the radii of the cations. The structure of EuTiO₃Cl and DyTiO₃Cl was refined to R = 3.4% and R = 5.8% respectively. The crystal structure which has a certain similarity to brannerite can be described in a simplified way by saying that the rare earth and chlorine particles are located between walls of Ti? O-double-octahedra.     

Synthetic,Structural, and Spectroscopic Investigations of K3Nb8O21‐type Complex Oxides K3MTa7O21 (M = Ti,Zr)

Potassium‐containing zirconium(IV)/titanium(IV) tantalum(V) oxides, K₃TiTa₇O₂₁ ( 1 ) and K₃ZrTa₇O₂₁ ( 2 ), of K₃Nb₈O₂₁‐type of compounds are afforded from potassium‐molybdate flux. Both compounds crystallize in the hexagonal space group P6₃/mcm (no. 193) with a = 908.69(2), c = 1202.83(7) pm and c/a = 1.324 (Z = 2) for 1 and a = 913.30(3), c = 1219.21(6) pm and c/a = 1.335 (Z = 2) for 2 , respectively. The Structural motif of [MTa₇O₂₁]^3– (M = Ti⁴⁺ or Zr⁴⁺) consists of edge‐shared (M,Ta)₆O₂₄‐units that are similar to corner‐sharing Ta₆O₂₇ units of synthetic soro‐silicate K₃Ta₃Si₂O₁₃ and double borate K₃Ta₃B₂O₁₂. The solid state bandgap measurements revealed that calculated values (3.26 eV for K₃TiTa₇O₂₁ and 3.14 eV for K₃ZrTa₇O₂₁) are dependent on aperture of Ta–O–Ta bond angle as it was previously shown for perovskite‐type tantalate photocatalysts.     

ChemInform Abstract: Low‐Lying Electronic States of M3O9‐ and M3O92‐ (M: Mo,W)

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Präparation,Kristallstruktur und thermisches Verhalten der Quecksilber(I)phosphate α-(Hg2)3(PO4)2, β-(Hg2)3(PO4)2 und (Hg2)2P2O7

Contributions on Crystal Structures and Thermal Behaviour of Anhydrous Phosphates. XXIII. Preparation, Crystal Structure, and Thermal Behaviour of the Mercury(I) Phosphates α-(Hg₂)₃(PO₄)₂, β-(Hg₂)₃(PO₄)₂, and (Hg₂)₂P₂O₇ Light-yellow single crystals of (Hg₂)₂P₂O₇ have been obtained via chemical vapour transport in a temperature gradient (500 °C → 450 °C, 23 d) using Hg₂Cl₂ as transport agent. Characteristic feature of the crystal structure (P2/n, Z = 2, a = 9,186(1), b = 4,902(1), c = 9,484(1) Å, β = 98,82(2)°, 1228 independent of 5004 reflections, R(F) = 0,066 for 61 variables, 7 atoms in the asymmetric unit) are Hg₂²⁺-units with d(Hg1–Hg1) = 2,508 Å and d(Hg2–Hg2) = 2,519 Å. The dumbbells Hg₂²⁺ are coordinated by oxygen, thus forming polyhedra [(Hg1₂)O₄] and [(Hg2₂)O₆]. These polyhedra share some oxygen atoms. In addition they are linked by the diphosphate anion P₂O₇^4– (ecliptic conformation; ∠(P,O,P) = 129°) to built up the 3-dimensional structure. Under hydrothermal conditions (T = 400 °C) orange single crystals of the mercury(I) orthophosphates α-(Hg₂)₃(PO₄)₂ and β-(Hg₂)₃(PO₄)₂ have been obtained from (Hg₂)₂P₂O₇ and H₃PO₄ (c = 1%). The crystal structures of both modifications have been refined from X-ray single crystal data [α-form (β-form): P2₁/c (P2₁/n), Z = 2 (2), a = 8,576(3) (7,869(3)), b = 4,956(1) (8,059(3)), c = 15,436(3) (9,217(4)) Å, β = 128,16(3) (108,76(4))°, 1218 (1602) independent reflections of 4339 (6358) reflections, R(F) = 0,039 (0,048) for 74 (74) variables, 8 (8) atoms in the asymmetric unit]. In the structure of α-(Hg₂)₃(PO₄)₂ three crystallographically independent mercury atoms, located in two independent dumbbells, are coordinated by three oxygen atoms each. Thus, [(Hg₂)O₆] dimers with a strongly distorted tetrahedral coordination of all mercury atoms are formed. Such dimers are present besides [(Hg₂)O₅]-polyhedra in the less dense crystal structure of β-(Hg₂)₃(PO₄)₂ (d(Hg–Hg) = 2,518 Å). The mercury(I) phosphates are thermally labile and disproportionate between 200 °C (β-(Hg₂)₃(PO₄)₂) and 480 °C (α-(Hg₂)₃(PO₄)₂) to elemental mercury and the corresponding mercury(II) phosphate.     

Zur Struktur von Thiophosphinsäuren Die Kristall- und Molekülstruktur der Dimethylthiophosphinsäure, (CH3)2PSOH,und der Dicyclohexylthiophosphinsäure, (C6H11)2PSOH,bei 140 K

Structure of Thiophosphinic Acids. Crystal and Molecular Structure of Dimethylthiophosphinic Acid and of Dicyclohexylthiophosphinic Acid The structures of dimethylthiophosphinic acid (HMTP) and of dicyclohexylthiophosphinic acid (HCTP) have been determined at 140 K by single crystal X-ray diffraction with 1245 and 2697 independent reflections, and refined to R = 0.023 and 0.025, respectively. HMTP crystallizes triclinic, space group P1 , with a = 6.168(2), b = 6.494(2), c = 6.893(2) Å, α = 79.52(1)°, β = 84.70(1)° and γ = 87.40(1)°; HCTP crystallizes triclinic, space group P1 with a = 8.570(2), b = 8.837(2), c = 9.760(2) Å, α = 70.95(2)°, β = 70.38(2)°, γ = 82.14(2)°. The unit cells of both compounds contain 2 molecules, which form centrosymmetric dimers by nearly linear O? H…?S hydrogen bonds. The O…?S bond distances are 3.121(1) and 3,143(1) Å, respectively. The vibrational spectra of HMTP have been reassigned.