VO4 Tetrahedra Research Articles

Growth and Properties of Single Crystals of Noncentrosymmetric Na3VO2B6O11

A new nonlinear optical crystal, Na3VO2B6O11, has been grown by the top-seeded solution growth method using a Na2CO3−V2O5 flux. The structure of the compound was determined by single-crystal X-ray diffraction. It crystallizes in the noncentrosymmetric orthorhombic system, space group P212121, with cell parameters a = 7.7359(9) Å, b = 10.1884(12) Å, c = 12.5697(15) Å, V = 990.7(2) Å3, and Z = 4. Na3VO2B6O11 has a three-dimensional structure consisting of hexaborate groups connected by VO4 tetrahedra with the sodium atoms distributed in channels through out the three-dimensional network. The refractive indices have been measured by the minimum deviation technique and fit to the Sellmeier equations. Nonlinear optical measurements on the compound demonstrate that the material has second harmonic generation properties, with an efficiency approximately the same as that of KH2PO4.

Crystal structure, electrical, and thermal properties of Ca0.5Th0.5VO4

Ca0.5Th0.5VO4 was prepared by a solid-state reaction of component oxides and characterized by powder x-ray diffraction (XRD) at ambient and higher temperatures and impedance spectroscopy. Crystal structure was refined by Rietveld refinements from powder XRD data. At room temperature, Ca0.5Th0.5VO4 has a zircon-type tetragonal (I41/amd) lattice with unit cell parameters: a = 7.2650(1) and c = 6.4460(1) Å. Despite the large charge difference, Ca2+ and Th4+ are statistically distributed over a single site. The crystal structure of Ca0.5Th0.5VO4 is built from the (Ca/Th)O8 (bisdisphenoid) and VO4 tetrahedra. The in situ high-temperature XRD studies on Ca0.5Th0.5VO4 revealed anisotropic thermal expansion behavior with coefficients of thermal expansion αc = 10.96 × 10−6/°C and αa = 5.32 × 10−6/°C. The impedance measurements carried out in the temperature range from ambient to 800 °C indicate semiconducting behavior with appreciable ionic conductivity above 400 °C. The activation energy obtained from the temperature-dependent AC conductivity data is ∼1.37 eV. In wider range of frequencies and temperatures, the relative permittivity of approximately 50 to 60 is observed for Ca0.5Th0.5VO4.

New sign of vacuum ultraviolet driven crystal growth in ternary oxide Zn 3 V 2 O 8 films

Ternary oxide Zn3V2O8 films was successfully formed on glass substrates only by means of vacuum ultraviolet irradiation to the spin-coated metal–organic solutions. From Fourier transform infrared spectroscopy measurements, we confirmed that the crystal growth proceeded at metal–organic bond cleavage under VUV irradiation. The crystalline size of the obtained materials was estimated to be 1.5–2.5 nm. The prepared Zn3V2O8 films clearly showed yellow luminescence, corresponding to a charge transfer transition in the VO4 tetrahedra.

Hydrothermal syntheses and crystal structures of two organic–inorganic hybrid molybdovanadates based on [V2Mo6(OH)2O24]4− and [VMo12O40]3− polyoxoanions

Two new organic–inorganic hybrid cobalt-molybdovanadates [Co(phen)3]H2[H2V2Mo6O26] · 7H2O (1) and [Co(2,2′-bipy)3][Na(H2O)7][VMo12O40] (2) have been hydrothermally synthesized and structurally characterized by elemental analyses, IR, UV, XPS spectroscopy, thermogravimetric (TG) analyses, and X-ray single crystal diffraction. The molecular structure of 1 consists of a [V2Mo6(OH)2O24]4− polyoxoanion, a [Co(phen)3]2+, two H+ and seven lattice water molecules. The structure of [V2Mo6(OH)2O24]4− consists of six MoO6 octahedra and two VO4 tetrahedra; six MoO6 octahedra are linked by edge-sharing oxygens forming a {Mo6} ring, and two VO4 tetrahedra cap opposite sides of the {Mo6} ring. The molecular structural unit of 2 is constructed from a typical Keggin-type [VMo12O40]3− polyoxoanion and a [Co(2,2′-bipy)3]2+ cation and a Na+ countercation; Co2+ is coordinated by six nitrogens from three 2,2′-bipyridines forming a distorted octahedron.

Preparation and characterization of Mesopoous VO x/SBA-16 and their application for the direct catalytic hydroxylation of benzene to phenol

Vanadium oxide supported on mesoporous SBA-16 (VO x /SBA-16) catalysts have been prepared by the impregnation method and characterized by small-angle XRD, wide-angle XRD, TEM, N 2-physisorption, DRUV–vis, Raman spectrum and H 2-TPR. The VO x /SBA-16 catalysts retained the cubic cage-like pore structure of SBA-16. The dispersion and the nature of the vanadium species depend strongly on the V amount. At V loading of less than 3.6 wt%, isolated tetrahedral VO 4 is the main existence species that is highly dispersed in the pores of the support SBA-16. With the increase in V loading, the aggregation of isolated tetrahedral VO 4 species occurred to form polymerized VO 4 units. When the V loading was above 5.5 wt%, nanostructured V 2O 5 crystallites were formed besides aggregation of polymerized VO 4 units. VO x /SBA-16 with 7.3 wt% V showed excellent activity for the hydroxylation of benzene. The effect of reaction time, temperature and the amount of catalyst was investigated over VO x /SBA-16 (7.3 wt%) catalyst. The highest phenol yield and turnover number were 13.8% and 32.4, respectively, which were attributed to the formation of highly dispersed VO 4 species and polymerized VO 4 units. The TON and yield of phenol also increase in the presence of the V 2O 5 crystallites but its selectivity decreases.

Performance and Characterization of ALD Vanadium Oxide Catalytic Nanoliths

Supported vanadium oxide species are active catalysts for the selective, oxidative conversion of hydrocarbons to useful chemicals. Both the catalytic vanadium oxide and the supporting oxide were synthesized by ALD on high surface powders and anodic aluminum oxide (AAO) nanoliths. The nanoliths were prepared by anodic oxidation of aluminum. 1 nm of ALD aluminum oxide acts as the support for vanadium oxide loaded by 1 to 18 ALD cycles of vanadyltri-isopropoxide/H2O2. Ultraviolet-visible absorption edges red shift as the vanadia loading increases. The edge energy of 1-cycle ALD VOx corresponds to isolated, tetrahedral VO4 in agreement with Raman spectroscopy. V-O-V bonds form with additional cycles producing a gradual increase in VOx domain size. Reaction rate coefficients for the oxidative dehydrogenation of cyclohexane show increased overall activity in the high loading catalysts but a higher specific activity in the low loading catalysts for cyclohexene formation.

Low temperature powder diffraction and DFT solid state computational study of hydrogen bonding in NH4VO3

AbstractThe crystal structure of NH4VO3 was refined by the geometry optimization done by total energy minimization in solid state using DFT/plane waves approach. The lattice parameters were derived by the Le Bail technique from the low temperature X‐ray (40‐293 K) and synchrotron (100‐293 K) powder diffraction data. The structure is formed by the infinite chains of irregular VO4 tetrahedra running approximately parallel to the c‐axis, which are interlinked by the ammonium ions placed between them. The ammonium ions link to the [VO4]∞ chains through one linear, one bifurcated and two trifurcated N‐H…O hydrogen bonds. Considering their stability there are six distinct N‐H…O hydrogen bonds: two strong with the N‐H…O bond angles close to the straight, two medium with the bond angles of 123° and 148° and two very bent (105° and 107°) and hence weak hydrogen bonds. There is a reasonable agreement between the energies of the stretching ν(NH) modes estimated using the optimised N…O contact distances and those obtained experimentally. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of the Vanadyl Bond Ordering and Analysis of the Spin Exchange Interactions in Pb2V3O9 and Pb2As2VO9

The structures of Pb2V3O9 and Pb2As2VO9 were determined by X-ray diffraction to settle the issue concerning whether the arrangement of the V4+═O vanadyl bonds is ordered or disordered. The new crystal structure of Pb2V3O9 refined by using a twinned crystal differs from the previous structure, determined from a combined use of powder X-ray and neutron diffraction data, and suggests an ordered Ferro arrangement of the V4+═O vanadyl bonds as does the Antiferro crystal structure of the new Pb2As2VO9. In Pb2V3O9, a triclinic → monoclinic transition is observed at 400 °C, and the corresponding high temperature form was structurally characterized. The spin exchange interactions of Pb2V3O9 and Pb2As2VO9 were evaluated by performing qualitative spin dimer analysis based on tight binding calculations, and those of Pb2V3O9 were also examined by quantitative mapping analysis based on density functional theory calculations. To a first approximation, the spin−lattice of Pb2V3O9 is described by an alternating antiferromagnetic chain model, which is made up of the super-superexchange interactions mediated by VO4 tetrahedra between adjacent chains of corner-sharing V4+O6 octahedra. The magnetic property of Pb2As2VO9 is predicted to be paramagnetic, in agreement with experiment.

Soft chemistry synthesis and crystal structure of Mg xCu 3− xV 2O 6(OH) 4·2H 2O

Mg x Cu 3− x V 2O 6(OH) 4·2H 2O ( x ∼ 1), with similar crystal structure as volborthite Cu 3V 2O 7(OH) 2·2H 2O, was successfully prepared by a soft chemistry technique. The method consists of mixing magnesium nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V 2O 5 with few mL of 30 vol.% H 2O 2 followed by addition of distilled water). When ammonium hydroxide NH 4OH 10% was added (pH 7.8), a green yellowish precipitate was obtained. Using X-ray powder diffraction data, its crystal structure has been determined by Rietveld refinement. Compared to volborthite, the vanadium coordination changes from tetrahedral VO 4 to trigonal bipyramidal VO 5, and magnesium replaces copper, preferably, in the less distorted octahedron. At 300 °C, the phase formed is similar to the high pressure (HP) monoclinic Cu 3V 2O 8 phase. However at higher temperature, 600 °C, the phase obtained is different from known Cu 3V 2O 8 phases.

Active sites in vanadia/titania catalysts for selective aerial oxidation of β-picoline to nicotinic acid

Vanadia/titania catalysts with varying vanadium content were prepared by impregnation using three different titania carrier materials of varying surface area. The structure of active vanadium species for β-picoline oxidation was investigated. Vanadium is mainly in the +5 oxidation state as revealed by electron paramagnetic resonance (EPR) and 51V magic-angle spinning nuclear magnetic resonance ( 51V MAS NMR) spectroscopy techniques. Diffuse reflectance UV–visible (DRUV–vis) spectroscopy and spectral deconvolution enabled identification of at least five different types of vanadium oxide species in these catalysts: monomeric tetrahedral VO 3− 4, polymeric distorted tetrahedral VO − 3, square pyramidal V 2O 5, octahedral V 2O 2− 6 and V 4+ oxide species. While both VO 3− 4 and VO − 3 species are active in β-picoline oxidation, the latter having a distorted tetrahedral geometry yielded the desired products—picolinaldehyde and nicotinic acid. High surface area, anatase structure for the support and dispersed, distorted tetrahedral vanadium oxide species are the key parameters determining the activity and selectivity of these oxidation catalysts.

Electronic structure of the weakly coupled edge-sharingMnO4 spin- chain compound LiMnVO4: an ab initio study

Based on fully self-consistent first-principles density functional theory(DFT) calculations as well as classical spin analysis, we study the electronicstructure and magnetic interactions of the spinel-related compoundLiMnVO4. Four possible ordered spin states have been considered by spin-polarized generalizedgradient approximation (GGA) calculations. The antiferromagnetic (AFM) configurationwith both intra-chain and inter-chain AFM coupling interactions is energetically favorableamong these magnetic ordered states. The calculated AFM solution agrees well witha series of experimental measurements. The intra-atomic exchange splitting ofthe Mn 3d spin-up and spin-down states results in the insulating behavior ofLiMnVO4. The Heisenberg Hamiltonian is used to deduce the magnetic coupling parametersby adopting Noodleman’s broken symmetry method. The intra-chain AFMinteractions are much stronger than the inter-chain AFM interactions and thusLiMnVO4 can be described as a weakly coupled edge-sharing spin chain system. We propose that the presence of the side groups of edge-sharingLiO4 and VO4 tetrahedra are contributing to the intra-chain AFM interactions in the nearly90° Mn–O–Mn bond configuration of the edge-sharingMnO4 chains.

Chiral Helices in a 3D Network of Zn<sub>2</sub>(en)V<sub>2</sub>O<sub>7</sub> (en = Ethylenediamine)

An inorganic-organic hybrid vanadate complex, Zn2(en)V2O7 (en = ethylenediamine) has been hydrothermally synthesized and characterized by single-crystal X-ray crystallography, TG analysis, IR spectroscopy, and elemental analysis. The title compound crystallizes in the monoclinic space group P21 with a = 7.0885(7), b = 8.6040(9), c = 8.1869(8) Å, b = 112.224(2)° and V = 462.22(8) Å3, T = 298±2 K and R1[I>2s(I)] = 0.0291 for 2170 observed reflections. The structure consists of undulating sheets constructed from helical chains that share Zn coordination centers with repeating units propagated into a helix by the two-fold screw axes at 0, y, ½ and pillared with alternating VO4 tetrahedra to generate a 3D chiral network. Neighboring helices are interconnected by µ2-O bridges to form the three-dimensional network. The strength of the network is reinforced by hydrogen bonding. TG analysis shows thermal stability of the network up to 283 °C.

57Fe-Mössbauer study of electrically conducting barium iron vanadate glass after heat treatment

Local structure and thermal durability of semiconducting xBaO·(90 − x)V2O5 · 10Fe2O3 glasses (x = 20, 30 and 40), NTA glass TM, before and after isothermal annealing were investigated by 57Fe-Mossbauer spectroscopy and differential thermal analysis (DTA). An identical isomer shift (\(\mathit{\delta}\)) of 0.39 ± 0.01 mm s − 1 and a systematic increase in the quadrupole splitting (Δ) were observed from 0.70 ± 0.02 to 0.80 ± 0.02 mm s − 1 with an increasing BaO content, showing an increase in the local distortion of FeIIIO4 tetrahedra. From the slope of the straight line in the T g–Δ plot of NTA glass TM, it proved that FeIII plays a role of network former. Large Debye temperature (Θ D) values of 1000 and 486 K were respectively obtained for 20BaO · 70V2O5 · 10Fe2O3 glass before and after isothermal annealing at 400°C for 60 min, respectively. This result also suggests that FeIII atoms constitute the glass network composed of tetrahedral FeO4, tetrahedral VO4 and pyramidal VO5 units. The electric conductivity of 20BaO · 70V2O5 · 10Fe2O3 glass increased from 1.6 × 10 − 5 to 5.8 × 10 − 2 S cm − 1 after isothermal annealing at 450°C for 2,000 min. These results suggest that the drastic increase in the electric conductivity caused by heat treatment is closely related to the structural relaxation of the glass network structure.

Hydrate von Li3VO4: Synthese und Strukturchemie / Hydrates of Li3VO4: Synthesis and Structural Chemistry

Stoichiometric hydrates of Li3VO4, the hexahydrate and two polymorphs of the octahydrate, were prepared by evaporation of alkaline aqueous solutions 1 molar in LiOH and 0.5 molar in the metavanadate LiVO3 at r. t. with or without the addition of Lithium sulfide, i. e. at different pH values. Their crystal structures have been determined and refined using single crystal X-ray data; all lithium and hydrogen atom positions were localised and refined without contraints. All three title compounds crystallise in non-centrosymmetric space groups. The water molecules belong to the tetrahedral coordination spheres of the Li cations, i. e. they are embedded as water of coordination exclusively. The tetrahedral orthovanadate(V) anions VO3− 4 and the LiO4 tetrahedra are connected via common O corners to form building units which are further held together by strong, nearly linear hydrogen bonds. The hexahydrate Li3VO4 ・ 6H2O (space group R3, a = 962.9(2), c = 869.2(2) pm, Z = 3, R1 = 0.0260) contains isolated orthovanadate(V) anions VO3− 4 surrounded by a 3D network of cornersharing Li(H2O)4 tetrahedra forming rings of three, seven and eight units. The water molecules are ‘isolated’ in the sense that no hydrogen bonds are formed between water molecules. The octahydrate is dimorphous: The triclinic polymorph of Li3VO4 ・ 8H2O (space group P1, a = 592.6(2), b = 651.3(2), c = 730.2(4) pm, α = 89.09(2), β = 89.43(2), γ = 88.968(12)°, Z = 1, R1 = 0.0325) contains two types of chains of tetrahedra: One consists of corner-sharing Li(H2O)4 tetrahedra only, the second one is formed by alternating LiO4 and VO4 tetrahedra, also sharing oxygen corners. Only one water molecule is ‘isolated’, the other seven form a branched fragment of a chain with hydrogen bonds between them. In the monoclinic form of Li3VO4・8H2O (space group Pc, a = 732.6(1), b = 653.7(1), c = 1292.9(3) pm, β = 112.21(1)°, Z = 2, R1 = 0.0289) a fragment of a chain of three LiO4 tetrahedra, two of which share a common edge, and one VO4 tetrahedron represent the formular unit. These building blocks are connected via hydrogen bonds formed by three ‘isolated’ water molecules and a chain fragment of five connected water molecules.

Hydrothermal Synthesis and Crystal Structure of AgVMO5 (M: Se, Te).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Mechanism of cation migration at high temperature in chabazite

Page s293 Acta Cryst. (2007). A63, s293 compounds and K3Nd(PO4)2 are isostructural and crystallize in the monoclinic system with space group P21/m and Pearson symbol mP28. Least square refinements gave rise to the above indicated formulas which are consistent with the chemical analysis results. The structure of those vanadates is built up of two independent VO4 tetrahedra sharing edge or corner with LaO7 polyhedron. However, a small difference between the two structures has been observed. Indeed, the Rb1,435Cs1,565La(VO4)2 structure includes tree larger sites in nineand ten-coordinate environments, two disordered nine-coordinate Cs/Rb positions with occupancies 0.33/0.17 and 0.45/0.05, respectively, and one tencoordinate Rb position, whereas, in that of K1,125Rb1,875La(VO4)2 the potassium and rubidium ions are disordered over two large cation positions with nine and ten-neighbouring oxygen (occupancies rates Rb/K are 0.33/0.17 and 0.11/0.39, respectively) and one rubidium with eleven-coordinate environments. The V-O and La-O bond lengths vary from 1.674 to 1.733 A and from 2.397 to 2.616 A, respectively, in both structures. These values are compatible with those published in the literature for similar vanadates without disorder like K2CsLa(VO4)2. The infrared and Raman spectra of these two compounds have been established and interpreted. The attribution of vibrationnal spectra was proposed by a study of Raman and infrared spectra. This attribution was confirmed by an analysis in normal coordinates. The simulation of the vibration spectra can be regarded as satisfying since the average deviation between the calculated frequencies and the observed ones is approximately 1,5%.

Hydrothermal Synthesis and Crystal Structure of AgVMO5 (M = Se, Te)

AbstractSingle crystals of AgVSeO5 and AgVTeO5 were obtained under hydrothermal conditions at 190 °C by reacting stoichiometric amounts of AgNO3, NaVO3, TeO2 and SeO2, respectively. AgVSeO5 crystallizes in Pbcm with a = 418.14(3) pm, b = 2007.70(6) pm, c = 521.17(2) pm, V = 437.52(2) × 106 pm3 and Z = 4, as red needles. The structure consists of VO5 square pyramids, trigonal SeO3 pyramids and AgO8 polyhedra, as primary building units. The VO5 square pyramids are linked to chains running along the c‐axis, by sharing oxygen atoms in the basal plane in cis‐position. The remaining basal O atoms of the VO5 moieties are shared with two oxygen atoms of the SeO3 units. The resulting polyanionic strands of composition [VSeO5]− are interconnected by silver atoms to form a three dimensional network. AgVTeO5 crystallizes as yellow needles in P21/c with a = 586.59(1) pm, b = 1137.98(2) pm, c = 680.78(1) pm, β = 102.733(1)°, V = 443.26(1) × 106 pm3 and Z = 4. The structure consists of VO4 tetrahedra, Ψ‐trigonal‐bipyramidal TeO4 units and AgO8 polyhedra as primary building units. The TeO4 groups form dimers by edge sharing, which are linked through vertices to the VO4 tetrahedra. The resulting one dimensional polyanion is extending along [101]. The structural motifs and charge distribution according to Se4+/V5+, and Te4+/V5+ respectively, seem to allow for a reshuffling of the charge distribution, thus inducing interesting physical phenomena, at elevated temperatures or pressures.

Triclinic apatites

Apatites commonly adopt P6(3)/m hexagonal symmetry. More rarely, monoclinic chemical analogues have been recognized, including the biologically significant hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), but the driving force towards lower symmetry has not been systematically examined. A combination of diffraction observations and ab initio calculations for Ca(10)(AsO(4))(6)F(2) and Ca(10)(VO(4))(6)F(2) show these materials are triclinic P\bar 1 apatites in which the AsO(4) and VO(4) tetrahedra tilt to relieve stress at the metal and metalloid sites to yield reasonable bond-valence sums. An analysis of the triclinic non-stoichiometric apatites La(10 - x)(GeO(4))(6)O(3 - 1.5x) and Ca(10)(PO(4))(6)(OH)(2 - x)O(x/2) confirms this scheme of tetrahedral rotations, while Cd(10)(PO(4))(6)F(2) and Ca(10)(CrO(4))(6)F(2) are predicted to be isostructural. These distortions are in contrast to the better known P112(1)/b monoclinic dimorphs of chloroapatite and hydroxyapatite, where the impetus for symmetry reduction is ordered anion (OH(-) and Cl(-)) displacements which are necessary to obtain acceptable bond lengths. These results are important for designing apatites with specific structural and crystal-chemical characteristics.

Raman investigations of rare earth orthovanadates

Polarized Raman spectroscopy has been used to obtain the room-temperature phonon spectra of the series of rare earth orthovanadate single crystals: SmVO4, HoVO4, YbVO4, and LuVO4. The observed Raman frequencies follow the overall mode distribution expected for REVO4 compounds with the tetragonal zircon structure. The variation of the mode frequency with atomic number across the lanthanide orthovanadate series was investigated, and the trend exhibited by the internal modes was explained by considering the force constants of VO4 tetrahedron.

(Ph3Sn)3VO4]·CH3CN und [(Ph3Sn)3VO4]·2 DMF, Triphenylzinnvanadate mit neuartigen Kettenstrukturen

Abstract[(Ph3Sn)3VO4]·CH3CN and [(Ph3Sn)3VO4]·2 DMF, Triphenyltin Vanadates with Novel Chain StructuresThe reaction of Na3VO4 with Ph3SnCl in a water/CH2Cl2 mixture leads to the formation of [(Ph3Sn)3VO4] (1). Recrystallization of 1 from toluene/CH3CN gives pale yellow crystals of [(Ph3Sn)3VO4]·CH3CN (2). 2 crystallizes as coordination polymer which consists of infinite chains composed of corner‐sharing VO4 tetrahedra and Ph3SnO2 trigonal bipyramides. Additionally the VO4 groups are connected to two terminal SnPh3‐Groups containing tin atoms in a tetrahedral environment. [(Ph3Sn)3VO4]·2 DMF (3) which is obtained from Na3VO4 and Ph3SnCl in a water/DMF mixture contains a polymeric chain structure similar to 2 and additionally one of the terminal SnPh3 groups is coordinated to a DMF solvent molecule.