Comparison of the force field in various pyrochlore families. II. Phases presenting structural defects

A previous study of various A₂B₂O₆O′ pyrochlore families by vibrational spectroscopy allowed the analysis of the ir and Raman spectra and the force fields of pyrochlore phases presenting structural defects. The spectra of the following compounds were compared: (i) ideal pyrochlore Cd₂Ta₂O₇, (ii) lacunary Tl₂Ta₂O₆, (iii) nonstoichiometric Pb_1.5Ta₂O_6.5, and (iv) Pb_2.3Ta₂O_7.3 exhibiting regular shear planes. If the tridimensional network of TaO₆ octahedra is not modified and the perturbations concern only the A₄O′ tetrahedra network, a slight modification of the vibrational spectra and a weak decrease in the TaO stretching and OTaO bending force constants are observed. But, if the octahedra network is perturbed, large modifications appear on the spectra, revealing unambiguously the existence of new types of bonds created by the defects in the structure. The Raman intense lines observed in the low frequency range in lead compounds is also discussed.     

An XPS depth-profile study on electrochemically deposited TaO x

Through the use of XPS and controlled Ar⁺ etching, the surface composition and oxide species of tantalum oxides (TaO _x ), which were electrodeposited on glassy carbon electrodes by cyclic voltammetric and constant-potential electrolyses, are quantified along the depth profile. Electrodeposition exhibits efficacy in depositing TaO _x with a distribution of various TaO _x : TaO, TaO₂, and Ta₂O₅. The distribution gradient from the outer surface of TaO _x is such that Ta₂O₅?>?TaO₂?>?TaO. TaO is found to be the dominant species in the underlying layer of TaO _x . Such a unique structure of the electrode surface is analogous to that of nanoparticles with a core–shell structure, with the core being suboxides and the surface being that of the saturated pentoxide, Ta₂O₅. The electrochemically induced nonhydrolytic condensation route is proposed to be capable of producing TaO _x with a distribution gradient of Ta₂O₅, TaO₂, and TaO in the depth direction.     

catena‐Poly­[[bis­(hexa­fluoro­acetyl­acetonato‐κ2O,O′)­zinc(II)]‐μ‐4,4′‐bi­pyridine‐κ2N:N′]

The structure of the title compound, catena‐poly[[bis(1,1,1,5,5,5‐hexafluoropentane‐2,4‐dionato‐κ²O,O′)zinc(III)]‐μ‐4,4′‐bipyridine‐κ²N:N′], [Zn(C₅HF₆O₂)₂(C₁₀H₈N₂)]_n, con­sists of polymeric chains, running in two perpendicular directions, organized as planes normal to the tetragonal axis. The elemental unit of the chains is the zinc(II) coordination polyhedron bisected by a twofold symmetry axis, and thus only half of the unit is independent. The octahedral coordination geometry of the metal centre is composed of two oxy­gen‐chelating (symmetry‐related) hexa­fluoro­acetyl­acetonate groups and two translationally related 4,4′‐bi­pyridine groups, which act as connecting agents in the polymer structure. The stabilization of this architecture of chains and planes is associated with a number of weak C—H⋯O and C—H⋯F hydrogen bonds.     

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.     

Poly[dimethyldiphenylphosphonium [di‐μ4‐iodido‐tetra‐μ3‐iodido‐pentacopper(I)]]

The title compound, {(C₁₄H₁₆P)[Cu₅I₆]}_n, prepared from the reaction between copper powder, iodine and dimethyldiphenylphosphonium iodide in hydroxyacetone, features an anion that consists of a continuous two‐dimensional Cu–I sheet [Cu—I = 2.5960 (14)–2.6994 (13) Å and Cu—I—Cu = 63.28 (5)–114.25 (5)°]. The cation, which lies on a mirror plane, is a typical dimethyldiphenylphosphonium ion. The structure shows a strong tendency towards segregation of the inorganic and organic parts of the structure into separate subspaces. The two‐dimensional Cu–I sheet displays a pronounced subcell with pseudo‐tetragonal symmetry that is broken by ordered vacancies on the Cu position. The symmetry is further reduced by the orientation of the interleaved organic counter‐ion that is inclined with respect to the pseudo‐mirror planes defined by the Cu–I sheet normal, perpendicular to the b axis.     

Zur kenntnis ‚Kationen-reicher’︁ Tantalate und Niobate Über Na5TaO5 und Na5NbO5

On Tantalates and Niobates ‘rich in Cations’. On Na₅TaO₅ and Na₅NbO₅ Colourless, transparent single crystals of Na₅TaO₅ [annealed mixtures of Na₂O, Li₂O, and Ta₂O₅, Na : Li : Ta = 6.6 : 1.1 : 1, Ni-cylinder, 1000°C, 75 d] as well as Na₅NbO₅ [annealed mixtures of Na₂O, Li₂O, and Nb₂O₅, Na : Li : Nb = 6.6 : 1.1 : 1, Ni-cylinder, 1000°C, 75 d] have been prepared. Single crystal data show that both isotypic oxides represent a deformed variant of the NaCl-type of structure [Na₅TaO₅: 1154 from 1250 I₀ (hkl), four-cycle diffractometer Philips PW 1100, ω2-θ scan, Ag? Kα , R = 4.88%, space group c2/c with a = 629.3(1) pm, b = 1025.4(2) pm, c = 1004.6(2) pm, b? 106.80(2)°, z = 4 and Na₅NbO₅: 998 from 1247 I₀(hkl), four-cycle diffractometer Philips PW 1100, ω-2θ scan, Ag? Kα , R = 8.58% and R_w = 7.67%, space group C2/2 with a = 629.1(1) pm, b = 1024.4(2) pm, c = 1004.2(2) pm, b? = 106.80(2)°, Z = 4]. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, the latter derived from Mean Effective Fictive Ionic Radii, MEFIR, as well as Charge Distribution, CHARDI, are calculated.     

Bi3TaO7/MXene纳米片异质结的制备及光催化降解磺胺嘧啶钠

分别以五水合硝酸铋（Bi （NO₃）₃·5H₂O）和五氯化钽（TaCl₅）作为Bi源和Ta源,采用静电吸附和溶剂热法在2D Ti₃C₂的表面原位生长0D Bi₃TaO₇纳米颗粒制备Bi₃TaO₇/Ti₃C₂复合光催化材料。通过各种物理化学表征研究了2D Ti₃C₂纳米片对Bi₃TaO₇/Ti₃C₂复合光催化材料微结构的影响。通过可见光下降解磺胺嘧啶钠（SD-Na）溶液来评价所制备样品的光催化性能。实验结果表明,Bi₃TaO₇/Ti₃C₂复合材料的光催化性能明显增强。在最优条件下（Ti₃C₂与Bi₃TaO₇的质量比为0.02）制备的BT2展现出最高的光催化活性,其降解SD-Na溶液的表观速率常数是纯Bi₃TaO₇的2.8倍。Bi₃TaO₇/Ti₃C₂复合光催化材料性能的显著提高归因于Ti₃C₂/Bi₃TaO₇异质结的形成有利于光生载流子的快速转移和分离。     

Synthesis and photophysical properties of 2,5,8,11‐tetrakis(5‐hexylthiophen‐2‐yl)tetrathieno[2,3‐a:3′,2′‐c:2′′,3′′‐f:3′′′,2′′′‐h]naphthalene

The title compound, C₅₈H₆₄S₈, has been prepared by Pd‐catalysed direct C—H arylation of tetrathienonaphthalene (TTN) with 5‐hexyl‐2‐iodothiophene and recrystallized by slow evaporation from dichloromethane. The crystal structure shows a completely planar geometry of the TTN core, crystallizing in the monoclinic space group P2₁/c. The structure consists of slipped π‐stacks and the interfacial distance between the mean planes of the TTN cores is 3.456 (5) Å, which is slightly larger than that of the comparable derivative of tetrathienoanthracene (TTA) with 2‐hexylthiophene groups. The packing in the two structures is greatly influenced by both the aromatic core of the structure and the alkyl side chains.     

Fluorite-related phases Ln3MO7, Ln = rare earth,Y or Sc,M = Nb,Sb, or Ta: II. Structure determination

The crystal structures of the orthorhombic fluorite-related compounds La₃NbO₇ (Cmcm), Y₃TaO₇, and Y₂GdSbO₇, (C222₁) have been determined from X-ray powder diffraction intensities and single-crystal electron diffraction data. The structures are basically similar. One third of the Ln cations are 8-coordinated, and lie in [001] rows which alternate with parallel rows of corner-linked MO₆ coordination octahedra within slabs parallel to (100). The remaining Ln cations lie in between these slabs in seven-fold coordination. This interslab cation arrangement distinguishes the structure from the closely related pyrochlore (A₂B₂O₇) and weberite (Na₂MgAlF₇) structures. The compounds YGdScSbO₇ and Nd₂ScNbO₇, also examined, have the pyrochlore structure, with Sc and Sb, or Sc and Nb distributed on the octahedral B sites.     

Ein neues Oxotantalat(V): Über KLi6[TaO6] [1]

A New Oxotantalate(V): On KLi₆[TaO₆] [1] For the first time hitherto unknown KLi₆[TaO₆] was obtained by intimately pulverized mixtures of K₂O, Li₂O and Ta₂O₅ (molar ratio K:Li:Ta = 1.1:6.6:1) in a closed Ni-cylinder (800°C, 30 d) in form of colourless single crystals; trigonal-rhomboedral (space group R3 m) with a = 822.6(1) pm, c = 721.2(1) pm (Guinier-Simonpowder data), Z = 3. The determination of the crystal structure (four cycle diffractometer data, 224 out of 224 I₀ (hkl), R = 1.80%, R_w = 1.79%, absorption not considered) proves that KLi₆[TaO₆] is isotypic with KLi₆[IrO₆], a stuffed derivative of the α-Li₆[UO₆] structure type. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, the latter derived from Mean Effective Ionic Radii, MEFIR, as well as the Charge Distribution, CHARDI, are calculated and discussed.     

Preparation and Characterization of GdTaO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> Sol-Gel Luminescence Thin Films

High quality GdTaO₄:Eu³⁺ luminescence films have been successfully prepared through a modified sol-gel process. The films were prepared using inorganic materials as raw materials, and the thermal decomposition and UV assisted technique were introduced to improve the quality of the film and reduce the period for forming the thick film. Results of structural studies by atomic force microscopy (AFM) and X-ray diffraction (XRD) showed that the surface was smooth and the structure was monoclinic with the average grain size of about 55 nm. The emission and excitation spectra of the film were investigated. Related to the transition ⁵ D₀ →⁷ F₁ and ⁵ D₀→⁷ F₂ of Eu³⁺ ions, the main luminescence peaks were observed at 591 and 611 nm respectively, and the luminescence peak at 345 nm was detected simultaneously related to the TaO₄³⁻ emission. Transmission spectrum and decay curve of the luminescence are also presented in this paper.     

1‐[2‐(4‐Nitro­phenoxy)­acetyl]­pyrroli­din‐2‐one: an antiamnesic agent

The title compound, C₁₂H₁₂N₂O₅, is a potential antiamnesic agent. The pyrrolidinone ring has an envelope conformation, and the central moiety is almost coplanar with the planes of the phenyl and pyrrolidinone rings. In the crystal structure, weak intermolecular C—H...O interactions link the mol­ecules into a complex network that can be described by (X) rings (X = 16, 20 and 26) and a C(12) chain.     

Order–disorder phase transformations in quaternary pyrochlore oxide system: Investigated by X-ray diffraction, transmission electron microscopy and Raman spectroscopic techniques

Order–disorder transformations in a quaternary pyrochlore oxide system, Ca–Y–Zr–Ta–O, were studied by powder X-ray diffraction (XRD) method, transmission electron microscope (TEM) and FT-NIR Raman spectroscopic techniques. The solid solutions in different ratios, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, of CaTaO_3.5 and YZrO_3.5 were prepared by the conventional high temperature ceramic route. The XRD results and Rietveld analysis revealed that the crystal structure changed from an ordered pyrochlore structure to a disordered defect fluorite structure as the ratios of the solid solutions of CaTaO_3.5 and YZrO_3.5 were changed from 4:1 to 1:4. This structural transformation in the present system is attributed to the lowering of the average cation radius ratio, r_A/r_B as a result of progressive and simultaneous substitution of larger cation Ca²⁺ for Y³⁺ at A sites and smaller cation Ta⁵⁺ for Zr⁴⁺ at B sites. Raman spectroscopy and TEM analysis corroborated the XRD results.     

An X‐ray powder diffraction study of cis‐dichloridobis(2‐methyl‐2H‐tetrazol‐5‐amine‐κN4)platinum(II), a tetrazole‐containing analogue of cisplatin

The structure of the title compound, cis‐[PtCl₂(C₂H₅N₅)₂], was analysed using in‐house X‐ray powder diffraction data at room temperature. The structure was solved by direct methods and refined using Rietveld analysis. A slightly distorted square‐planar coordination geometry is formed around the Pt atom by two Cl atoms and two ring N atoms of the 2‐methyl‐2H‐tetrazol‐5‐amine ligands, which are in a cis configuration. The planes of the tetrazole rings are inclined at 79.7 (7) and 73.8 (6)° with respect to the coordination plane, with their substituents oriented in such a way that the complex as a whole has approximate C₂ symmetry. Intermolecular N—H...Cl hydrogen bonds mediate the formation of a three‐dimensional supramolecular network.     

The six‐membered‐ring azomethine N‐((E)‐{5‐[(E)‐(pyridin‐3‐ylimino)methyl]thiophen‐2‐yl}methylidene)pyridin‐3‐amine

The title compound, C₁₆H₁₂N₄S, forms a three‐dimensional layered network structure via intermolecular hydrogen bonding and π‐stacking. The azomethine molecule adopts the thermodynamically stable E regioisomer and the pyridine substituents are antiperiplanar. The mean planes of the pyridine rings and the azomethine group to which they are connected are twisted by 27.27 (5) and 33.60 (5)°. The electrochemical energy gap of 2.3 eV based on the HOMO–LUMO energy difference is in agreement with the spectroscopically derived value.     

Pyrochlore‐type tin niobate

A single crystal of Sn_1.59Nb_1.84O_6.35 was grown at 1273 K from a mixture of sodium niobate and tin(II) chloride. The structure is of pyrochlore type A₂B₂O₇. The tin is partially oxidized to tin(IV) and competes with niobium for the occupation of site B. The stereoactivity of the Sn²⁺ lone pair induces displacement of tin towards the O atoms of the tunnel.     

Highly Active GaN‐Stabilized Ta3N5 Thin‐Film Photoanode for Solar Water Oxidation

Ta₃N₅ is a very promising photocatalyst for solar water splitting because of its wide spectrum solar energy utilization up to 600 nm and suitable energy band position straddling the water splitting redox reactions. However, its development has long been impeded by poor compatibility with electrolytes. Herein, we demonstrate a simple sputtering‐nitridation process to fabricate high‐performance Ta₃N₅ film photoanodes owing to successful synthesis of the vital TaO_δ precursors. An effective GaN coating strategy is developed to remarkably stabilize Ta₃N₅ by forming a crystalline nitride‐on‐nitride structure with an improved nitride/electrolyte interface. A stable, high photocurrent density of 8 mA cm⁻² was obtained with a CoPi/GaN/Ta₃N₅ photoanode at 1.2 V_RHE under simulated sunlight, with O₂ and H₂ generated at a Faraday efficiency of unity over 12 h. Our vapor‐phase deposition method can be used to fabricate high‐performance (oxy)nitrides for practical photoelectrochemical applications.     

Long- and short-range order in stuffed titanate pyrochlores

We report a structural study of the stuffed pyrochlore series Ln₂(Ti_2−xLn_x)O_7−x/2 (Ln=Ho, Yb; 0?x?0.67). Electron microscopy and Rietveld refinements of neutron powder diffraction data for the x=0.67 end members, Ho₂TiO₅ and Yb₂TiO₅, reveal that small domains (∼50 Å or less) exist where the Ln and Ti/Ln sublattices are pyrochlore like, while the average structure is fluorite like. Both the Ho and Yb stuffed pyrochlore series for 0.1?x?0.5 are shown to be a composite of long- and short-range-ordered pyrochlore phases. The relative fraction of long-range vs. short-range pyrochlore order decreases with increasing Ln doping. An additional complex structural modulation of the pyrochlore structure is observed in electron diffraction and high-resolution electron microscopy images.     

Penta­aqua­oxovanadium(IV) bis(trifluoro­methane­sulfonate)

The structure of the penta­aqua­oxo­vanadium(IV) ion in a salt with singly charged counter‐ions is presented. In [VO(H₂O)₅](CF₃SO₃)₂, the six‐coordinate V atom is coordinated to the oxo group with a short bond [1.577 (2) Å]. The equatorial V—O bond lengths are 2.0262 (18) and 2.0277 (17) Å. The aqua ligand trans to the oxo group is subject to its trans influence, which leads to a somewhat longer V—O bond [2.175 (2) Å]. In the structure, the cation and both anions are situated on crystallographic mirror planes. The cation and anions engage in a number of relatively long hydrogen bonds [2.725 (2)–2.834 (2) Å].     

(E)‐4‐(4‐Bromo­phenyl­diazen­yl)‐2,6‐dimethyl­phenyl acrylate and (E)‐2,6‐dimethyl‐4‐(4‐methyl­phenyl­diazen­yl)­phenyl acrylate

The crystal structures of the title compounds, C₁₇H₁₅BrN₂O₂, (I), and C₁₈H₁₈N₂O₂, (II), determined at room temperature, have a trans configuration with respect to the diazene linkage, as found for other azo (diazene) derivatives. The aromatic mean planes are nearly coplanar, with a dihedral angle between these planes of 8.31 (2)° for (I) and 3.74 (2)° for (II). In both complexes, the mean plane of the ester group is nearly perpendicular to the aromatic ring planes. In both compounds, the crystal packing involves only π–π and π–ring inter­actions, which combine to stabilize the extended structure.