High‐temperature mass spectrometric study of the vaporization processes in the system CaO‐MgO‐Al2O3‐Cr2O3‐FeO‐SiO2

Knudsen effusion mass spectrometry was used to study vaporization processes and thermodynamic properties of twenty samples of chromium‐containing slags in the CaO‐MgO‐Al₂O₃‐Cr₂O₃‐FeO‐SiO₂ system in the temperature range 1850–2750 K. Tungsten cells were used and Cr₂O₃ solid was used as a reference material. The system was calibrated using liquid gold. As FeO was the first emanating vapor species, monitoring of the chromium‐containing species could be carried out only after the complete vaporization of FeO. This, however, was found to have very little impact on the concentration of the slags investigated. During the measurements, the ion current intensities of CrO⁺ and CrO species in the mass spectra of the vapor over the CaO‐MgO‐Al₂O₃‐Cr₂O₃‐FeO‐SiO₂ samples were monitored and compared with those corresponding to solid Cr₂O₃. Data on the partial pressures of vapor species as well as the activities of Cr₂O₃ as a function of temperature were obtained. The results are expected to be valuable in the optimization of slag composition in high alloy steelmaking processes. Copyright © 2009 John Wiley & Sons, Ltd.     

High‐performance Flexible Complementary Electrochromic Device Based on Plasma Modified WO3 Nano Hybrids and V2O5 Nanofilm with Low Operation Voltages

Tungsten trioxide‐poly(3,4‐ethylenedioxythiophene) (WO₃‐PEDOT) and tungsten trioxide‐polyfuran (WO₃‐PFu) were prepared by rf rotating plasma polymerization. Electrochromic hybrid thin films were fabricated onto flexible polyethylene terephthalate (PET)/ indium tin oxide (ITO) film using electron beam evaporation method. In order to deeply characterize all films, scanning electron microscopy‐energy dispersive X‐ray spectroscopy (SEM‐EDS) and electrochemical impedance spectroscopy (EIS) techniques were used. The counter electrode effect on plasma modified WO₃ nano hybrids‐based electrochromic devices (ECDs) was evaluated. By incorporating flexible vanadium pentoxide (V₂O₅) film as counter electrode, complementary ECDs were constructed through combining the hybrid flexible films (WO₃‐PEDOT, WO₃‐PFu) as working electrodes, which exhibit highly efficient electrochromic performance with low voltage operation. Especially, WO₃‐PEDOT/V₂O₅‐based ECD owns a high optical modulation of 61.5 % at 750 nm driven by −1.0 V (coloration) and +1 V (bleaching) with fast response times (coloration time: 13.58 s, bleaching time: 8.07 s) and a high coloration efficiency of 527 cm² C⁻¹. This study can supply useful and efficient avenue for designing flexible complementary electrochromic device for energy‐saving flexible electronics.     

Effect of Nitrogen Substitution in V2O3 on the Metal–Insulator Transition

The effect of N‐doping on the paramagnetic–antiferromagnetic transition associated with the metal–insulator (M–I) transition of V₂O₃ at 150 K has been studied in bulk samples as well as in nanosheets. The magnetic transition temperature of V₂O₃ is lowered to ～120 K in the N‐doped samples. Electrical resistivity data also indicate a similar lowering of the M–I transition temperature. First‐principles DFT calculations reveal that anionic (N) substitution and the accompanying oxygen vacancies reduce the energy of the high‐temperature metallic corundum phase relative to the monoclinic one leading to the observed reduction in Nèel temperature. In the electronic structure of N‐substituted V₂O₃, a sub‐band of 2p states of trivalent anion (N) associated with its strong bond with the vanadium cation appears at the top of the band of O(2p) states, the 3d‐states of V being slightly higher in energy. Its band gap is thus due to crystal field splitting of the degenerate d‐orbitals of vanadium and superexchange interaction, which reduces notably (ΔE_g=?0.4 eV) due to their hybridization with the 2p states of nitrogen. A weak magnetic moment arises in the monoclinic phase of N‐substituted V₂O₃ with O‐vacancies, with a moment of ?1 μ_B/N localized on vanadium atoms in the vicinity of oxygen vacancies.     

Disordered structure of ZrW1.8V0.2O7.9 from a combined X‐ray and neutron powder diffraction study at 530 K

A novel compound, vanadium aliovalent substituted zirconium tungstate, ZrW_1.8V_0.2O_7.9, was prepared with vanadium substituting tungsten rather than the common zirconium substitution. The structure of the high‐temperature phase was refined from combined neutron and X‐ray powder diffraction data gathered at 530 K. This phase is the disordered centric modification (space group Pa) and the average crystal structure is similar to that of β‐ZrW₂O₈. The V atom occupies only a W2 site and charge compensation is achieved through oxygen vacancy, i.e. the oxygen vacancy occurs at only the O4 site. [Atom names follow the established scheme; Evans et al. (1996). Chem. Mater. 8 , 2809–2823.]     

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.     

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.     

A non‐oxo methanolate‐bridged divanadium(IV) complex with tris(2‐sulfanidylphenyl)phosphane ligands: synthesis,structural characterization and magnetic investigation

Vanadium chemistry is of interest due its biological relevance and medical applications. In particular, the interactions of high‐valent vanadium ions with sulfur‐containing biologically important molecules, such as cysteine and glutathione, might be related to the redox conversion of vanadium in ascidians, the function of amavadin (a vanadium‐containing anion) and the antidiabetic behaviour of vanadium compounds. A mechanistic understanding of these aspects is important. In an effort to investigate high‐valent vanadium–sulfur chemistry, we have synthesized and characterized the non‐oxo divanadium(IV) complex salt tetraphenylphosphonium tri‐μ‐<!?tlsb=‐0.11pt>methanolato‐κ⁶O:O‐bis({tris[2‐sulfanidyl‐3‐(trimethylsilyl)phenyl]phosphane‐κ⁴P,S,S′,S′′}vanadium(IV)) methanol disolvate, (C₂₄H₂₀P)[V^IV₂(μ‐OCH₃)₃(C₂₇H₃₆PS₃)₂]·2CH₃OH. Two V^IV metal centres are bridged by three methanolate ligands, giving a C2‐symmetric V₂(μ‐OMe)₃ core structure. Each V^IV centre adopts a monocapped trigonal antiprismatic geometry, with the P atom situated in the capping position and the three S atoms and three O atoms forming two triangular faces of the trigonal antiprism. The magnetic data indicate a paramagnetic nature of the salt, with an S = 1 spin state.     

catena‐Poly[[(2,2′‐bipyridyl)oxidovanadium]‐di‐μ2‐oxido‐[(2,2′‐bipyridyl)oxidovanadium]‐μ3‐selenito‐bis[(2,2′‐bipyridyl)dioxidovanadium]‐μ3‐selenito]

In the title compound, [V₄O₈(SeO₃)₂(C₁₀H₈N₂)₄], there are two distinct vanadium coordination environments. Alternating corner‐shared VO₄N₂ octahedra and SeO₃ pyramids result in eight‐membered centrosymmetric V₂Se₂O₄ rings. In addition, pairs of V centres form centrosymmetric V₂O₆N₄ clusters via edge‐sharing. These two kinds of secondary building units are linked in an ABABAB fashion to give an infinite chain whose nature is unprecedented in Se–V–O systems.     

The Use of Laser Induced Breakdown Spectroscopy (LIBS) to Study Catalyst Deactivation of V2O5/γ‐Al2O3 as Compared to Inductively Coupled Plasma Optical Emission Spectrometry

Laser Induced Breakdown Spectroscopy (LIBS) method is introduced as a novel approach in this work to study catalyst deactivation of V₂O₅/γ‐‐Al₂O₃ for gas‐phase dehydration of glycerol and producing acrolein. The LIBS results of V₂O₅/γ‐Al₂O₃ samples are compared with those data that are obtained by Inductively Coupled Plasma Optical Emission Spectrometry (ICP‐OES). Experimental data of LIBS data specify that line intensities of vanadium are decreased by deactivation of V₂O₅/γ‐Al₂O₃ catalyst. A comparison between the results of LIBS test as well as ICP‐OES analysis shows that the amount of vanadium is decreased in the catalyst. Moreover, coke formation changes the surface of the catalyst. The results of deactivation of V₂O₅/γ‐Al₂O₃ are also compared with Pd/C catalyst deactivation.     

Tungsten doped mesoporous SBA‐16 as novel heterogeneous catalysts for oxidation of cyclopentene to glutaric acid

Novel heterogeneous tungsten species in mesoporous silica SBA‐16 catalysts based on ship‐in‐a‐bottle methodology are originally reported for oxidizing cyclopentene (CPE) to glutaric acid (GAC) using hydrogen peroxide (H₂O₂). For all W‐SBA‐16 catalysts, isolated tungsten species and octahedrally coordinated tungsten oxide species are observed while WO₃ crystallites are detected for the W‐SBA‐16 catalysts with Si/ W = 5, 10, and 20. The specific surface areas and the corresponding total pore volumes decrease significantly as increasing amounts of tungsten incorporated into the pores of SBA‐16. Using tungsten‐substituted mesoporous SBA‐16 heterogeneous catalysts, high yield of GAC (55%) is achieved with low tungsten loading (for Si/W = 30, ~13 wt%) for oxidation of CPE. The W‐SBA‐16 catalysts with Si/W = 30 can be reused five times without dramatic deactivation. In fact, low catalytic activity provided by bulk WO₃ implies that the highly distributed tungsten species in SBA‐16 and the steric confinement effect of SBA‐16 are key elements for the outstanding catalytic performance.     

Unprecedented High‐Nuclear Transition‐Metal‐Cluster‐Substituted Heteropolyoxoniobates: Synthesis by {V8} Ring Insertion into the POM Matrix and Antitumor Activities

Reactions of hexaniobate with vanadate in the presence of Ni²⁺, Zn²⁺, or Cu²⁺ have furnished three high‐nuclear vanadium cluster‐substituted heteropolyoxoniobates (HPNs): {Ni(en)₃}₅H{V^VNb₈V^IV₈O₄₄} ? 9 H₂O ( 1 ), (H₂en)Na₂[{Zn(en)₂(Hen)}{Zn(en)₂(H₂O)}₂{PNb₈V^IV₈O₄₄}] ? 11 H₂O ( 2 ), and Na{Cu(en)₂}₃{[Cu(en)₂]₂[PNb₈V^IV₈O₄₄]} ? 11 H₂O ( 3 ) (en=1,2‐diaminoethane). Their structures have been determined and characterized by single‐crystal X‐ray diffraction analysis, thermogravimetric analysis (TGA), and elemental analysis. Structural analysis has revealed that compounds 1 – 3 contain similar {V₈}‐substituted [X^VNb₈V^IV₈O₄₄]^11? (X=P, V) clusters, obtained by inserting a {V₈} ring into tetravacant HPN [XNb₈O₃₆]^27?. To the best of our knowledge, compounds 1 – 3 represent the first high‐nuclear vanadium cluster‐substituted HPNs, and compound 1 is the largest vanadoniobate cluster yet obtained in HPN chemistry. Nickel and zinc cations have been introduced into HPNs for the first time, which might promise a more diverse set of structures in this family. Antitumor studies have indicated that compounds 1 and 2 exhibit high activity against human gastric cancer SGC‐7901 cells, SC‐1680 cells, and MG‐63 cells.     

Syntheses,Structures and Magnetic Behaviours of two Mixed‐Metal Inorganic‐Organic Hybrid Frameworks with N‐(Phosphonomethyl)iminodiacetate

Two mixed‐metal‐center inorganic‐organic hybrid frameworks incorporating N‐(Phosphonomethyl)iminodiacetate(H₄pmida), [Zn₂V₂O₂(pmida)₂(H₂O)₁₀]·H₂O ( 1 ) and [Zn₂V₂O₂(pmida)₂(H₂O)₁₂]·2H₂O ( 2 ), were synthesized by hydrothermal reactions and characterized by elemental analysis, IR spectra, UV‐Vis spectra and single crystal X‐ray analysis. In complex 1 , the centrosymmetric dimeric [V₂O₂(pmida)₂]^4– unit connected to neighboring Zn²⁺ through the phosphonate group, while 2 the [V₂O₂(pmida)₂]^4– unit uncoordinated with the Zn²⁺ in the presence of NaOH. Magnetic measurements in the range 2‐300 K have shown weak antiferromagnetic interaction between the adjacent vanadium ions in complexes.     

The Significance of Lewis Acid Sites for the Selective Catalytic Reduction of Nitric Oxide on Vanadium‐Based Catalysts

The long debated reaction mechanisms of the selective catalytic reduction (SCR) of nitric oxide with ammonia (NH₃) on vanadium‐based catalysts rely on the involvement of Brønsted or Lewis acid sites. This issue has been clearly elucidated using a combination of transient perturbations of the catalyst environment with operando time‐resolved spectroscopy to obtain unique molecular level insights. Nitric oxide reacts predominantly with NH₃ coordinated to Lewis sites on vanadia on tungsta–titania (V₂O₅‐WO₃‐TiO₂), while Brønsted sites are not involved in the catalytic cycle. The Lewis site is a mono‐oxo vanadyl group that reduces only in the presence of both nitric oxide and NH₃. We were also able to verify the formation of the nitrosamide (NH₂NO) intermediate, which forms in tandem with vanadium reduction, and thus the entire mechanism of SCR. Our experimental approach, demonstrated in the specific case of SCR, promises to progress the understanding of chemical reactions of technological relevance.     

A New Class of Homogeneous Visible‐Light Photocatalysts: Molecular Cerium Vanadium Oxide Clusters

The first systematic access to molecular cerium vanadium oxides is presented. A family of structurally related, di‐cerium‐functionalized vanadium oxide clusters and their use as visible‐light‐driven photooxidation catalysts is reported. Comparative analyses show that photocatalytic activity is controlled by the cluster architecture. Increased photoreactivity of the cerium vanadium oxides in the visible range compared with nonfunctionalized vanadates is observed. Based on the recent discovery of the first molecular cerium vanadate cluster, (nBu₄N)₂[(Ce(dmso)₃)₂V₁₂O₃₃Cl] ? 2 DMSO ( 1 ), two new di‐cerium‐containing vanadium oxide clusters [(Ce(dmso)₄)₂V₁₁O₃₀Cl] ? DMSO ( 2 ) and [(Ce(nmp)₄)₂V₁₂O₃₂Cl] ? NMP ? Me₂CO ( 3 ; NMP=N‐methyl‐2‐pyrrolidone) were obtained by using a novel fragmentation and reassembly route. Pentagonal building units {(V)M₅} (M=V, Ce) reminiscent of “Müller‐type” pentagons are observed in 2 and 3 . Compounds 1 – 3 feature high visible‐light photooxidative activity, and quantum efficiencies >10 % for indigo photooxidation are observed. Photocatalytic performance increases in the order 1 < 3 < 2 . Mechanistic studies show that the irradiation wavelength and the presence of oxygen strongly affect photoreactivity. Initial findings suggest that the photooxidation mechanism proceeds by intermediate formation of hydroxyl radicals. The findings open new avenues for the bottom‐up design of sunlight‐driven photocatalysts.     

Real‐time Observation of Deep Lithiation of Tungsten Oxide Nanowires by In Situ Electron Microscopy

An in‐depth mechanistic understanding of the electrochemical lithiation process of tungsten oxide (WO₃) is both of fundamental interest and relevant for potential applications. One of the most important features of WO₃ lithiation is the formation of the chemically flexible, nonstoichiometric Li_xWO₃, known as tungsten bronze. Herein, we achieved the real‐time observation of the deep electrochemical lithiation process of single‐crystal WO₃ nanowires by constructing in situ transmission electron microscopy (TEM) electrochemical cells. As revealed by nanoscale imaging, diffraction, and spectroscopy, it is shown that the rapid and deep lithiation of WO₃ nanowires leads to the formation of highly disordered and near‐amorphous Li_xWO₃ phases, but with no detectable traces of elemental W and segregated Li₂O phase formation. These results highlight the remarkable chemical and structural flexibility of the Li_xWO₃ phases in accommodating the rapid and deep lithiation reaction.     

Synthetic beta‐K0.33V2O5 Nanorods: A Metal–Insulator Transition in Vanadium Oxide Bronze

We found a linear relationship between the metal–insulator transition (MIT) temperature and the A⁺ ionic radius of the beta‐A_0.33V₂O₅ bronze family, leading our attention to beta‐K_0.33V₂O₅ which has been neglected for a long time. We have introduced a facile hydrothermal method to obtain the single‐crystalline beta‐K_0.33V₂O₅ nanorods. As expected, both the temperature‐dependence of the resistivity and magnetization demonstrated MITs at about 72 K for beta‐K_0.33V₂O₅, thus matching well with the linear relationship described above. The beta‐K_0.33V₂O₅ was assigned as a new member of the beta‐A_0.33V₂O₅ bronze family for their similar crystal and electronic structures and their MIT property; this addition enriches the beta‐A_0.33V₂O₅ bronze family.     

Pb2.63Cd2V3O12, a cation‐deficient garnet‐type vanadate

In the crystal structure of the cation‐deficient garnet Pb_2.63Cd₂V₃O₁₂ (lead cadmium vanadium oxide), the Cd and V atoms fully occupy octahedral and tetrahedral sites, respectively, whereas the Pb atoms partially occupy a dodecahedral site. The total Pb and Cd content indicates that vanadium is slightly reduced from the +5 oxidation state.     

Dinuclear Face‐Sharing Bi‐octahedral Tungsten(VI) Core and Unusual Thermal Behavior in Complex Th Tungstates

Two new thorium tungstates A₆Th₆(WO₄)₁₄O (A=K and Rb) were synthesized by high‐temperature solid‐state reactions. The structures of both phases are based on a rare dinuclear confacial bi‐octahedral [W₂O₉]^6? core, encapsulated in a [Th₆W₇O₄₆(W₂O₉)]^32? cage showing a cross‐section geometry similar to a six‐leafed lily. The adjacent cages are connected in two dimensional layers by WO₄ tetrahedral linkers. Due to the dissimilarities in mutual orientations of adjacent layers in these two structures, K₆Th₆(WO₄)₁₄O crystallizes in space group of R32 while Rb₆Th₆(WO₄)₁₄O stabilizes in P$\bar 6$ 2c. The high‐temperature phase transition was observed in Rb₆Th₆(WO₄)₁₄O and investigated using high‐temperature PXRD technique. The results demonstrate a very unusual thermal behavior of this compound. The Raman and IR spectra of both phases were analyzed with respect to their complex structures.     

Ba3V2S4O3: A Mott Insulating Frustrated Quasi‐One‐Dimensional S=1 Magnet

Through a solid‐state reaction, a practically phase pure powder of Ba₃V₂S₄O₃ was obtained. The crystal structure was confirmed by X‐ray single‐crystal and synchrotron X‐ray powder diffraction (P6₃, a=10.1620(2), c=5.93212(1) Å). X‐ray absorption spectroscopy, in conjunction with multiplet calculations, clearly describes the vanadium in charge‐disproportionated V^IIIS₆ and V^VSO₃ coordinations. The compound is shown to be a strongly correlated Mott insulator, which contradicts previous predictions. Magnetic and specific heat measurements suggest dominant antiferromagnetic spin interactions concomitant with a weak residual ferromagnetic component, and that intrinsic geometric frustration prevents long‐range order from evolving.     

Thin films of vanadium oxide grown on vanadium metal: oxidation conditions to produce V2O5 films for Li‐intercalation applications and characterisation by XPS,AFM, RBS/NRA

Thin films of vanadium oxide were grown on vanadium metal surfaces (i) in air at ambient conditions, (ii) in 5 mM H₂SO₄ (aq), pH 3, (iii) by thermal oxidation at low oxygen pressure (10^?5 mbar) at temperatures between 350 and 550 °C and (iv) at near‐atmospheric oxygen pressure (750 mbar) at 500 °C. The oxide films were investigated by atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), X‐Ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). The lithium intercalation properties were studied by cyclic voltammetry (CV). The results show that the oxide films formed in air at room temperature (RT), in acidic aqueous solution, and at low oxygen pressure at elevated temperatures are composed of V₂O₃. In air and in aqueous solution at RT, the oxide films are ultra‐thin and hydroxylated. At 500 °C, nearly atmospheric oxygen pressure is required to form crystalline V₂O₅ films. The oxide films grown at pO₂ = 750 mbar for 5 min are about 260‐nm thick, and consist of a 115‐nm outer layer of crystalline V₂O₅. The inner oxide is mainly composed of VO₂. For all high temperature oxidations, the oxygen diffusion from the oxide film into the metal matrix was considerable. The oxygen saturation of the metal at 450 °C was found, by XPS, to be 27 at.% at the oxide/metal interface. The well‐crystallized V₂O₅ film, formed by oxidation for 5 min at 500 °C and 750 mbar O₂, was shown to have good lithium intercalation properties and is a promising candidate as electrode material in lithium batteries. Copyright © 2005 John Wiley & Sons, Ltd.