Strontium Vanadium Oxide–Hydrides: “Square‐Planar” Two‐Electron Phases

A series of strontium vanadium oxide–hydride phases prepared by utilizing a low‐temperature synthesis strategy in which oxide ions in Sr_n+1V_nO_3n+1 (n=∞, 1, 2) phases are topochemically replaced by hydride ions to form SrVO₂H, Sr₂VO₃H, and Sr₃V₂O₅H₂, respectively. These new phases contain sheets or chains of apex‐linked V³⁺O₄ squares stacked with SrH layers/chains, such that the n=∞ member, SrVO₂H, can be considered to be analogous to “infinite‐layer” phases, such as Sr_1?xCa_xCuO₂ (the parent phase of the high‐T_c cuprate superconductors), but with a d² electron count. All three oxide–hydride phases exhibit strong antiferromagnetic coupling, with SrVO₂H exhibiting an antiferromagnetic ordering temperature, T_N>300 K. The strong antiferromagnetic couplings are surprising given they appear to arise from π‐type magnetic exchange.     

Influence of the nature of the conduction band of transition metal oxides on catalytic activity for oxygen reduction

Catalytic activities for oxygen reduction of some transition metal oxides with metallic conductivity such as LaTiO₃, SrFeO₃, SrVO₃, SrRuO₃, V_0.2Ti_1.8O₃ and La_1-xSr_xMnO₃ were investigated, and they as well as the activities of other oxides reported already were compared with the nature of their conduction bands. It was found that the catalytic activity of oxides having a σ^* conduction band was high. The conclusion is drawn that in order for a transition metal oxide to have a high catalytic activity, (1) it must have a σ^* band and (2) the band must contain electrons. This conclusion will be useful to predict the catalytic activity for oxygen reduction of transition metal oxides.     

Structural, Infrared, and Magnetic Characterization of the Solid Solution Series Sr2−xPbx(VO)(VO4)2; Evidence of the Pb6sLone Pair Stereochemical Effect

The solid solution Sr_2−xPb_xV₃O₉, 0≤x≤2, was prepared by solid state reactions and characterized by X-ray diffraction, IR spectroscopy, and magnetic susceptibility measurements. Single crystals of the pure strontium phase and mixed Sr/Pb compounds were prepared by high temperature treatment of the respective powder compositions. Pb₂V₃O₉crystals could only be obtained by the electrochemical reduction of molten PbV₂O₆. These crystals were always twinned. The previously reported crystal structure of Sr₂V₃O₉was confirmed. It was refined toR=0.050,R_w=0.057, in space group C2/c,a=7.555(1) Å,b=16.275(2) Å,c=6.948(1) Å,β=119.78(1)°. The single crystal structural studies of the Sr_1.02Pb_0.98V₃O₉and Sr_0.67Pb_1.33V₃O₉members of the series show that the introduction of lead gives rise to a progressively complicated splitting of Sr²⁺/Pb²⁺and the tetrahedral vanadium ion crystallographic sites. As a consequence the vanadium framework distorts and beyond the Sr_0.5Pb_1.5V₃O₉composition the crystal symmetry becomes triclinic. This distortion is ascribed to the stereochemical effect of the 6s²lone pair of Pb²⁺. The crystallographic parameters of Pb₂V₃O₉area=7.598(1) Å,b=16.393(3) Å,c=6.972(2) Å,α=91.38(1)°,β=119.35(1)°,γ=90.47(1)°. Pb₂V₃O₉exhibits a more complex IR spectrum than the monoclinic phases. Despite the similarity between the triclinic and monoclinic phases the magnetic susceptibilities indicate differences in the coupling between V⁴⁺ions at low temperatures.     

Oxygen permeation and phase structure properties of partially A-site substituted BaCo0.7Fe0.225Ta0.075O3-δ perovskites

Ba_0.9R_0.1Co_0.7Fe_0.225Ta_0.075O_3-δ (BRCFT, R = Ca, La or Sr) membranes were synthesized by a solid-state reaction. Metal cation Ca²⁺, La³⁺ or Sr²⁺ doping on A-site partially substituted Ba²⁺ in BaCo_0.7Fe_0.225Ta_0.075O_3-δ oxides, and its subsequent effects on phase structure stability, oxygen permeability and oxygen desorption were systematically investigated by XRD, TG-DSC, H₂-TPR, O₂-TPD techniques and oxygen permeation experiments. The partial substitution with Ca²⁺, La³⁺ or Sr²⁺, whose ionic radii are smaller than that of Ba²⁺, succeeded in stabilizing the cubic perovskite structure without formation of impurity phases, as revealed by XRD analysis. Oxygen-involving experiments showed that BRCFT with A-site fully occupied by Ba²⁺ exhibited good oxygen permeation flux under He flow, reaching about 2.3 mL·min⁻¹ ·cm⁻² at 900 °C with 1 mm thickness. Of all the membranes, BLCFT membrane showed better chemical stability in CO₂, owing to the reduction in alkalinity of the mixed conductor oxide by La doping. In addition, we also found the stability of the perovskite structure under reducing atmospheres was strengthened by increasing the size of A-site cation (Ba²⁺>La³⁺>Sr²⁺>Ca²⁺).     

Synthese und Kristallstruktur von BaVo2,5

Single crystals of BaVO_2,5 were prepared by high temperature LASER-technique under a hydrogen atmosphere. The X-ray investigation leads to a trigonal symmetry (a=571.8;c=1161.3 pm, space group C _3v ¹ -P3m 1). BaVO_2,5 consists of a closest sphere packing of oxygen with a sequence of cubic and hexagonal layers of the type ... ccchh ... The consequences in respect to the coordination of Ba²⁺ and V³⁺ are discussed.

     

Zur Kristallstruktur von Ba3In2O6

About the Crystal Structure of Ba₃In₂O₆ Single crystals of Ba₃In₂O₆ could be prepared by recrystallization of a flux and by solid state reaction in closed platinium tubes, respectively. Ba₃In₂O₆ crystallizes with tetragonal symmetry (space group 14/mmm, a = 4.1868; c = 21.7041 Å, Z = 2). Single crystal X-ray work lead to a crystal structure like La_2-xSr_1+xCu₂O_6-δ therefor Ba₃In₂O₆ is a modified member of the Sr₃Ti₂O₇-Type. The coordinations of Ba²⁺ and In³⁺ are described and the relations to the Sr₃Ti₂O₇-type are discussed.     

Reduction Processes in the Course of Mechanochemical Synthesis of Li1+xV3O8

Mechanical activation (MA) of the LiOH+V₂O₅ and Li₂CO₃+V₂O₅ mixtures followed by brief heating at 673 K was used to prepare dispersed Li_1+xV₃O₈. It was shown that structural transformations during MA are accompanied by reduction processes. EPR spectra of Li_1+xV₃O₈ are attributed to vanadyl VO²⁺ ions with weak exchange interaction. The interaction of localized electrons (V⁴⁺ ions) with electron gas (delocalized electrons), which is exhibited through the dependence of EPR line width of vanadium ions versus measurement temperature (C–S–C relaxation), is revealed. It is shown that C–S–C relaxation is different for intermediate and final products. The properties of mechanochemically prepared Li_1+xV₃O₈ are compared with those of HT-Li_1+xV₃O₈, obtained by conventional solid state reaction. Mechanochemically prepared Li_1+xV₃O₈ is characterized by a similar amount of vanadium ions, producing electron gas, but a higher specific surface area.     

A Molecular Placeholder Strategy To Access a Family of Transition‐Metal‐Functionalized Vanadium Oxide Clusters

Systematic access to metal‐functionalized polyoxometalates has thus far been limited to lacunary tungsten oxide and molybdenum oxide clusters. The first controlled, stepwise bottom‐up assembly route to metal‐functionalized molecular vanadium oxides is now presented. A di‐vacant vanadate cluster with two metal binding sites, (DMA)₂[V₁₂O₃₂Cl]^3? (DMA=dimethylammonium) is formed spontaneously in solution and characterized by single‐crystal X‐ray diffraction, ESI mass spectrometry, ⁵¹V NMR spectroscopy, and elemental analyses. In the cluster, the metal binding sites are selectively blocked by hydrogen‐bonded DMA placeholder cations. Reaction of the cluster with transition metals TM (Fe³⁺, Co²⁺, Cu²⁺, Zn²⁺) gives access to mono‐functionalized vanadate clusters (DMA)[{TM(L)}V₁₂O₃₂Cl]^n? (L=ligand). Metal binding is accomplished by significant distortions of the vanadium oxide framework reminiscent of a pincer movement. Cluster stability under technologically relevant conditions in the solid‐state and solution is demonstrated.     

Electrochemical behavior of single crystals of nonstoichiometric cerium(III) fluorides

The electrochemical properties of single crystals of cerium fluoride alloyed with bivalent cations Sr²⁺, Ca²⁺, Ba²⁺, Sr²⁺ + Ca²⁺, Sr²⁺ + Ba²⁺, Ba²⁺ + Ca²⁺ and also with La³⁺ and La³⁺ + Ba²⁺ cations are studied using the dynamic voltammetry and impedance spectroscopy. The conductivity of symmetrical cells with Ag electrodes is determined using the method of impedance spectroscopy in the frequency range from 450 to 5 kHz at the temperatures from 20 to 100°C: for CeF₃: Sr²⁺ (0.5 mol %) + Ba²⁺ (0.5 mol %), σ = σ₀ exp[(?0.284 ± 0.005/kT]; for CeF₃:Ca²⁺ (0.5 mol %) + Sr²⁺ (0.5 mol %), σ = σ₀ exp[(?0.292 ± 0.017/kT]. The steady-state and dynamic voltammogams of symmetrical electrochemical cells with nonpolarizable reference electrodes and CeF₃ single crystals alloyed with Sr²⁺, Ca²⁺, and Ba²⁺ bivalent cations exhibited ohmic polarization. For cells with CeF₃ containing La³⁺ as an admixture, a hysteresis was observed, which could not be eliminated by chemical and electrochemical treatment of crystals. In the dynamic voltammetric curves of asymmetric cells with nonpolarizable and silver electrode and CeF₃ crystals alloyed with Sr²⁺, Ca²⁺, and Ba²⁺, a range of ideal polarizability (from 0 to ～?2.7 V), and also cerium redox processes and silver fluorination-boundary regeneration were observed. In the dynamic voltammetric curves of asymmetric cells with CeF₃ containing La³⁺ admixture, no range of ideal polarizability was observed; however, the reactions of silver fluorination and reduction of solid-electrolyte cerium were well pronounced at the corresponding potentials.     

Analytical aspects of organic acids

Summary Phenyl acetic acid has been found to be a selective reagent for the estimation of zirconium. The acid gives a white crystalline precipitate which is quantitative between pH values of 3.00 to 5.40. As the composition of the precipitate varies somewhat, direct weighing is not possible and the compound is ignited to the oxide. The ions Be²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Mg²⁺, Ni²⁺, and Co²⁺ do not interfere, whereas the ions Fe³⁺, UO₂ ²⁺, Cr³⁺, Ba²⁺, Au⁺, Al³⁺, V₂O₄ ²⁺, Ti⁴⁺, Sn²⁺, and Ba²⁺ cause interferences in the estimation.

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Zusammenfassung Zur gravimetrischen Bestimmung von Zirkonium wird Phenylessigsäure empfohlen. Die weiße, kristalline Fällung ist im pH-Bereich 3,00–5,40 quantitativ. Infolge schwankender Zusammensetzung des Niederschlages ist eine direkte Wägung nicht möglich; er wird daher zum Oxid verglüht. Folgende Ionen stören nicht: Be²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Mg²⁺, Ni²⁺ und Co²⁺; dagegen verursachen Fe³⁺, UO₂ ²⁺, Cr³⁺, Ba²⁺, Au⁺, Al³⁺, V₂O₄ ²⁺, Ti⁴⁺, Sn²⁺ und Ba²⁺ Störungen bei der Bestim mung.

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Part VI: See Z. analyt. Chem. 175, 29 (1960).     

Effect of direct ultrasound synthesis via a sesquihydrate route on bismuth-promoted vanadyl pyrophosphate catalysts

A series of 1, 3, and 5% Bi-doped vanadium phosphate catalyst catalysts were prepared via sesquihydrate route using direct ultrasound method and were denoted as VPSB1, VPSB3, and VPSB5, respectively. These catalysts were synthesized solely using a direct ultrasound technique and calcined in a n-butane/air mixture. This study showed that catalyst synthesis time can be drastically reduced to only 2 hr compared to conventional 32–48 hr. All Bi-doped catalysts exhibited a well-crystallized (VO)₂P₂O₇ phase. In addition, two V⁵⁺ phases, that is, β-VOPO₄ and α_II-VOPO₄, were observed leading to an increase in the average oxidation state of vanadium. All catalysts showed V2p_3/2 at approx. 517 eV, giving the vanadium oxidation state at approx. 4.3–4.6. Field-emission scanning electron microscopy micrographs showed the secondary structure consisting of thin and small plate-like crystal clusters due to the cavitation effect of ultrasound waves. VPSB5 showed the highest amount of oxygen species removed associated with the V⁵⁺ and V⁴⁺ species in temperature-programmed reduction in H₂ analyses. TheX-ray absorption near edge structure (XANES) measurement showed the occurrence of vanadium oxide reductions in hydrogen gas flow, indicating the presence of V⁴⁺ and V⁵⁺ species. Higher average valence states of V⁵⁺, indicating more V⁵⁺ phases, were present. The addition of bismuth has increased the activity and selectivity to maleic anhydride.     

Züchtung von Einkristallen ternärer Lanthanoid-Vanadium(III)-oxide LnVO3 durch Schmelzflußelektrolyse

Growth of Single Crystals of Ternary Rare Earth Vanadium(III) Oxides LnVO₃ by Flux Electrolysis A simple method for growing single crystals of rare earth vanadium(III) oxides LnVO₃ (Ln = La, Sm, Gd, Dy, Er, Yb) by cathodic reduction, starting from vanadium(V) oxide, in a flux of sodium tetraborate and sodium fluoride at T = 1000 K is described. The products were obtained as black, prismatic crystals, suitable for X-ray investigations etc. They were characterized by electron microprobe analyses and by X-ray powder investigations.     

Reduction of nitrogen oxides with ammonia over complex vanadium and chromium oxides

Catalytic properties of -Al₂O₃ -supported complex vanadium and chromium oxides V_2–x Cr _x O_5– (0 < × s 1.3), amorphous to X-rays, in the reduction of nitrogen oxides with ammonia were studied. Vanadium exists in these catalysts mostly in a pentavalent state and chromium exists as Cr³⁺ and Cr⁶⁺. As the content of chromium in the catalysts increases, the optimal temperature of the process decreases, and the degree of conversion of nitrogen oxides increases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 339–342, February, 1996.     

The effect of carbonyl complexation on highly exothermic vanadium oxidation reactions

The effects of CO complexation on highly exothermic vanadium oxidation reactions is evaluated. We study the chemiluminescent (CL) reaction products formed when vanadium vapor entrained in Ar or CO is oxidized by O₃ or NO₂. The multiple collision V+Ar+O₃→VO^*(C ⁴Σ⁻, ⁴Φ, ²X)+Ar+O₂ reactive encounter yields two previously unreported VO excited states, whereas the V+Ar+NO₂→VO^*+Ar+NO reactive encounter populates states up to and including VO^* C ⁴Σ⁻. The multiple collision V+nCO+O₃ reactive encounter would appear to form a VOCO excited state complex, emitting in the region 420–560 nm, via the formation and oxidation of V(CO)₂ viz. V(CO)₂+O₃→VOCO^*+CO+O₂ and a relaxed VO excited state emitter via V+nCO+O₃→VO^*+nCO+O₂ where the VO excited state excitation is mediated by V–CO complexation. In complement, the much less exothermic V–NO₂ encounter displays an emission which, in concert with previous studies of CO complexation, suggests the formation of a VO(CO)₂ excited state complex viz. V(CO)₂+NO₂→VO(CO)₂^*+NO. The experiments characterizing CL are complemented by comparative laser-induced fluorescence studies of the VO X ⁴Σ⁻–CO and Ar interactions and their influence on the VO C ⁴Σ⁻–X ⁴Σ⁻ laser-induced excitation spectrum. These studies, in conjunction with further attempts to excite LIF in the 420–560 nm region, suggest that the observed complex emissions result primarily from VO excited state interactions. Complementary time-of-flight mass spectroscopy of vanadium and vanadium-oxide–carbonyl complex formation demonstrates the formation of V(CO), V(CO)₂, V₂(CO), and VOCO, the latter three of which demonstrate clear metastable-ion dissociation peaks for the processes VOCO⁺→V⁺+CO₂, V(CO)₂⁺→V⁺+2CO, and V₂(CO)⁺→V₂⁺+CO, suggesting that these vanadium complexes when formed in a reaction-based environment may be photodissociated with light in the visible and ultraviolet regions.     

Structural and magnetic study of the cation-ordered perovskites Ba2−xSrxErMoO6

A series of perovskite phases have been prepared from the appropriate carbonates and oxides by heating under reducing conditions at temperatures up to 1300 °C. Complete ordering between ErO₆ and MoO₆ octahedra and a disordered distribution of Sr²⁺ and Ba²⁺ occur in all compounds. Neutron powder diffraction experiments show that the substitution of Sr²⁺ into Ba₂ErMoO₆ introduces a progressive reduction in symmetry from Fm3¯m (x=0) to I4/m (x=0.5, 0.8) to P2₁/n (x=1.25, 1.75, 2.0). Magnetic susceptibility measurements indicate that all of these compounds show Curie-Weiss paramagnetism and that for x<1.25 this behaviour persists down to 2 K. The monoclinically distorted compounds show magnetic transitions at low temperature and neutron diffraction has confirmed the presence of long-range antiferromagnetic order below 2.5 and 4 K in Ba_0.25Sr_1.75ErMoO₆ and Sr₂ErMoO₆, respectively. Ba_0.75Sr_1.25ErMoO₆, Ba_0.25Sr_1.75ErMoO₆ and Sr₂ErMoO₆ do not undergo structural distortion on cooling from room temperature.     

Gamma irradiation induced photochemical reactions in V-doped borate glasses

Glasses of the composition XNa₂O · 4Al₂O₃ (96-X) B₂O₃ (mole%) where X = 10, 20, 30 to which 0.03 g V₂O₅ per 100 g glass was added, were prepared by normal melting. Their absorption characteristics together with the corresponding V-free base glasses were determined before and after gamma irradiation. The characteristic spectra of the unirradiated glasses show absorption bands at 315, 470, 560–580, 610–650, 700–870, and 860–1000 nm, indicating the presence of vanadium ions in more than one oxidation state, viz, V⁵⁺, V⁴⁺, and V³⁺. Gamma irradation of V-containing glasses causes the formation of color centers in the glass matrices, with absorption bands at 330, 500, and 610 nm, and photoreduced [V³⁺] and [V²⁺] ions with absorption bands at 350–355 and 530–570 and 520 nm, respectively. Photoreduced [V⁴⁺] may also be formed, giving rise to absorptions at 690–700 and 750–800 nm. The induced vanadium ions are found to absorb at shorter wavelengths than the intrinsic ones. An explanation based on the difference in the field energy of the two states is given.     

Characterization of thin metastable vanadium oxide films by Raman spectroscopy

Thin films are potentiodynamically generated on vanadium in Ba²⁺/acetate electrolyte systems at high voltages. The influence of the anodic potential up to 400 V on the composition and structure of the about 500 nm thin anodic conversion films are investigated. Raman spectroscopy indicates that different film types depend on the electrochemical process parameters. The relationship between the Raman laser excitation power and the amorphous or microcrystalline film structure is also discussed. Beside metastable disordered structures the films contain crystalline phases of V₂O₅, V₄O₉ and barium vanadate, respectively.     

Vanadium oxide anion cluster reactions with methyl isobutyrate and methyl methacrylate monomer and dimer: a study by FT/ICR mass spectrometry

Laser ablation of vanadium pentoxide (V₂O₅) powder produces VO₃⁻, V₂O₅⁻, V₃O₇⁻, V₃O₈⁻, and V₄O₁₀⁻ cluster ions which have subsequently been reacted with methyl isobutyrate, methyl methacrylate monomer and its dimer in the ion cell region of a Fourier transform ion cyclotron resonance mass spectrometer. Gas phase ion/molecule chemistry has revealed that reactivity decreases with increased mass of the vanadium oxide cluster anions. VO₃⁻, V₂O₅⁻, and V₃O₇⁻ ions react with the three reagents, methyl isobutyrate, methyl methacrylate and its dimer, respectively, either by addition of a whole reagent molecule or an associated fragment. All products formed are a result of parallel processes. V₄O₁₀⁻ undergoes no reaction for reaction times of up to 500 s, while V₃O₈⁻ adds a water molecule. Although the ions possess a net negative charge, the reactive site toward electron rich reagents such as methyl isobutyrate, methyl methacrylate and its dimer is the under-coordinated vanadium atom. This observation is supported by the lack of reactivity toward the studied reagents by those anions (V₃O₈⁻ and V₄O₁₀⁻) whose most likely stable structures contain fully coordinated vanadium atoms.     

Über gemischtvalente Ruthenium-Perowskite Ba3B3+Ru24,5+O9 – zur katalytischen Aktivität von Sauerstoffperowskiten mit vier- und fünfwertigen Edelmetallen

On Mixed Valent Perovskites Ba₃B³⁺Ru₂^4,5+O₉ – Catalytic Activity of Perovskite Oxides with Noble Metals The black compounds Ba₃B³⁺Ru₂O₉ crystallize with B³⁺ = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y in a hexagonal BaTiO₃ structure (6 L, sequence (hcc)₂) with an ordered distribution (1:2 order) of B³⁺ and ruthenium (BO₆ single octahedra; Ru₂O₉ double groups). The mean oxidation state of ruthenium is about +4.5. The properties are compared with that of other isotypic stacking polytypes Ba₃B³⁺M₂^4,5O₉ (M₂ = IrRu, Ir₂, PtRu) and Ba₃B²⁺M₂⁵⁺O₉ (M = Ru, Ir). The results of activity tests concerning the efficiency of perovskite oxides with noble metals in respect of the oxidation of CO or CH_x and the reduction of NO_x are reported.     

Donnees cristallographiques sur une nouvelle serie de manganites mixtes de terre rare et d'alcalino-terreux

The synthesis of two new series of oxides: BaLn₂Mn₂O₇ and SrLn₂Fe₂O₇, where Ln is a rare earth, was performed. The experimental conditions are given along with some crystal data. The diffraction patterns show a close resemblance with those of the double-perovskite-block compounds BaLn₂Fe₂O₇ and SrLn₂Fe₂O₇. However, the $\text{c}\text{a}$ ratio of the tetragonal cell is somewhat larger for the manganese compounds than for the iron compounds, due to a Jahn-Teller distortion of the Mn³⁺O₆ octahedral sites.