VO4 Tetrahedra Research Articles

Synthesis and structural characterization of the hexagonal anti-perovskite Na2CaVO4F

The structural details of the ordered hexagonal oxyfluoride Na2CaVO4F prepared by solid-state synthesis using stoichiometric amounts of V2O5, CaCO3, Na2CO3 and NaF were characterized using high-resolution neutron powder diffraction. The structural changes between 25°C and 750°C revealed that the two structural subunits in this material behave different when heated: there is an expansion of the face-shared FNa4Ca2 octahedra while the VO4 tetrahedra due to increased thermal disorder reveal marginal bond contractions. Bond valences and the global instability index point to significant structural disorder at 750°C.

The effect of the synthesis method on the morphological and luminescence characteristics of α-Zn2V2O7

A promising yellow phosphor, α-Zn2V2O7, was synthesized at temperatures below the phase transition temperature (610 ± 5°C) by three different methods: solid-phase and microwave processes and thermolysis of a water–salt composition. According to powder X-ray diffraction, the structures of all samples belonged to space group C/2c. Depending on the method of synthesis, the particle size varied from 500 nm (thermolysis of a water–salt composition) to 5–8 μm (ceramic and microwave methods). The excitation spectra of all samples are in the UV region (220–400 nm) and the emission spectra are in the 400–750 nm wavelength range. The photoluminescence spectra of the samples are non-elementary, which is caused by specific features of the electronic charge transfer in the structural VO4 tetrahedra.

Syntheses and structural characterization of vanado-tellurites and vanadyl-selenites: SrVTeO5(OH), Cd2V2Te2O11, Ca3VSe4O13·H2O and Ba2VSe3O10

Four new quaternary vanado-tellurites and vanadyl-selenites, namely, SrVTeO5(OH)(1), Cd2V2Te2O11(2), Ca3VSe4O13·H2O(3) and Ba2VSe3O10(4) have been synthesized and structurally characterized by single crystal X-ray diffraction. The oxidation state of vanadium is +5 in tellurites 1 and 2 and +4 in selenites 3 and 4. The structures of SrVTeO5(OH)(1) and Cd2V2Te2O11(2) compounds consist of (VTeO5(OH))2- and (V2Te2O11)4-anionic chains respectively, which are built from tetrahedral VO4 and disphenoidal TeO4 moieties. Similarly the structures of Ca3VSe4O13·H2O(3) and Ba2VSe3O10(4) respectively contain (VSe2O7)2- and (VSe3O10)4- anionic chains, which are made up of octahedral VO6 and pyramidal SeO3 units. Compounds 1 and 3 have been characterized by thermogravimetric and infrared spectroscopic methods. Compounds 1 and 2 are wide band gap semiconductors.

M3V2B10O23 (M = Ca, Sr): two new vanadoborates with [V2B10O23]∞ double layers

Ca3V2B10O23 and Sr3V2B10O23 are isostructural and their main frameworks are novel “infinite” 2D [V2B10O23]∞ double layers which composed of an [B5O9]∞ infinite layer and VO4 tetrahedra.

Manganese Vanadate Chemistry in Hydrothermal BaF2 Brines: Ba3Mn2(V2O7)2F2 and Ba7Mn8O2(VO4)2F23.

Manganese vanadate fluorides were synthesized using high-temperature hydrothermal techniques with BaF2 as a mineralizer. Ba3Mn2(V2O7)2F2 crystallizes in space group C2/c and consists of dimers built from edge-sharing MnO4F2 trigonal prisms with linking V2O7 groups. Ba7Mn8O2(VO4)2F23 crystallizes in space group Cmmm, with a manganese oxyfluoride network built from edge- and corner-sharing Mn2+/3+(O,F)6 octahedra. These octahedra form alternating Mn2+ and Mn2+/3+ layers separated by VO4 tetrahedra. This latter compound exhibits a canted antiferromagnetic order below TN = 25 K.

A new one-dimensional strontium vanadium tellurite, Sr7V4Te12O41.

Vanadium tellurites display a rich structural chemistry with interesting physical properties, such as second harmonic generation (SHG). Tellurites, i.e. Te(4+)Ox, are often observed in unusual structures and form various structural motifs, including isolated clusters, chains, layers, and three-dimensional networks. Similarly, vanadates, i.e. V(5+)Ox, show rich structural features, such as VO4 tetrahedra, VO5 square pyramids or trigonal bipyramids, and VO6 octahedra. Strontium vanadium tellurite, Sr7V4Te12O41, was obtained from the melt of the solid-state reaction of SrTeO4 and VO2 in a sealed quartz tube as it cooled from 973 K. The crystal structure exhibits a one-dimensional latticework along the a axis comprised of paired Sr3Te3Ox units, namely Sr6Te6O2x+1, with corner-shared TeO4 polyhedra - and specifically the Te lone-pair electrons - facing outward in the bc plane. The Sr6Te6O2x+1 latticework is helical and is layered in the b-axis direction against sheets of corner-shared VO4 tetrahedra, and is linked in the c-axis direction via individual corner-shared SrO8 square prisms.

Elucidation of Anchoring and Restructuring Steps during Synthesis of Silica-Supported Vanadium Oxide Catalysts

We investigate the chemical reactions involved during the synthesis of supported vanadium oxide catalysts using chemical grafting of vanadium oxytriisopropoxide (VO(OiPr)3) to thermally pretreated silica under solvent-free conditions. VO(OiPr)3 is found to react with both site-isolated silanol (Si−OH) groups and strained siloxane (≡Si−O−Si≡) bridges at the silica surface. Solid-state 51V and 13C MAS NMR confirms the formation of two slightly different vanadium species associated with the two anchoring mechanisms. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ Raman spectroscopy, and thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS) were used to study the subsequent calcination, revealing the formation of a transient V—OH intermediate upon the release of propene, followed by the formation of isolated VO4 surface species upon elimination of water. X-ray absorption spectroscopy (XAS) and 51V MAS NMR of the calcined material confirm the conversion of the two original vanadium sites to a species with a single isotropic shift, confirming the formation of isolated, tetrahedral VO4 sites.

Structural and magnetic characterization of the one-dimensionalS=5/2antiferromagnetic chain systemSrMn(VO4)(OH)

The descloizite-type compound, SrMn(VO4)(OH), was synthesized as large single crystals using a high-temperature high-pressure hydrothermal technique. X-ray single crystal structure analysis reveals that the material crystallizes in the acentric orthorhombic space group of P212121. The structure exhibits a one-dimensional feature, with MnO4 chains propagating along the a-axis which are interconnected by VO4 tetrahedra. Raman and infrared spectra were obtained to identify the fundamental vanadate and hydroxide vibrational modes. Magnetization data reveal a broad maximum at approximately 80 K, arising from one-dimensional magnetic correlations with intrachain exchange constant of J/kB = 9.97(3) K between nearest Mn neighbors and a canted antiferromagnetic behavior below TN = 30 K. Single crystal neutron diffraction at 4 K yielded a magnetic structure solution in the lower symmetry of the magnetic space group P21 with two unique chains displaying antiferromagnetically ordered Mn moments oriented nearly perpendicular to the chain axis. The presence of the Dzyaloshinskii Moriya antisymmetric exchange interaction leads to a slight canting of the spins and gives rise to a weak ferromagnetic component along the chain direction.

Synthesis and characterization of new fluoride-containing manganese vanadates A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F

Large single crystals of A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F were grown using a high-temperature (~600°C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO4F2 building blocks. The A2Mn2V2O7F2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb2Mn2V2O7F2: a=7.4389(17)Å, b=11.574(3)Å, c=10.914(2)Å; Cs2Mn2V2O7F2: a=7.5615(15)Å, b=11.745(2)Å, c=11.127(2)Å). The structure is composed of zigzag chains of edge-sharing MnO4F2 units running along the a-axis, and interconnected through V2O7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn2+ indicated that Cs2Mn2V2O7F2 is antiferromagnetic with a Neél temperature, TN=~3K and a Weiss constant, θ, of −11.7(1)K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs2Mn2V2O7F2. Mn2(VO4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2)Å, b=6.8036(7)Å, c=10.1408(13)Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn2+. These interpenetrating chains are additionally connected through isolated VO4 tetrahedra to form the condensed structure.

Single crystal structures of the new vanadates CuMgVO4 and AgMgVO4

The new compounds CuMgVO4 and AgMgVO4 have been synthesized by a solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data. CuMgVO4 crystallizes with Na2CrO4-type structure with space group Cmcm, a = 5.6932 (10), b = 8.7055 (15), c = 6.2789 (10) Å, V = 311.20 (9) Å3, and Z = 4, whereas AgMgVO4 crystallizes in the maricite-type structure with space group Pnma, a = 9.4286 (14), b = 6.7465 (10), c = 5.3360 (8) Å, V = 339.42 (9) Å3, and Z = 4. Both structures of CuMgVO4, and AgMgVO4 contain MgO4 chains made up of edge-sharing MgO6 octahedra. In CuMgVO4 the MgO4 chains are interconnected through CuVO4 double chains made up of VO4 and CuO4 tetrahedra sharing corners and edges, however in AgMgVO4 the chains are interlinked by the VO4 and AgO4 tetrahedra sharing only corners.

Structure, Raman and infrared spectroscopic properties of new nonlinear optical material Na3VO2B6O11

In this paper we report on the structure of Na3VO2B6O11 (NVBO) single crystals which were investigated by XRD, polarized Raman spectra in the range from 10 to 1600 cm−1 and infrared spectrum (IR) in the range from 100 to 1600 cm−1. Factor group analysis has been used to study the full vibrational representation of the crystal. More than 120 phonon modes have been obtained, which are related to BO and VO vibration in the trigonal planar BO3 triangle groups and tetrahedral BO4/VO4 groups. The high frequency bands located at 1300–1415 cm−1 are assigned to stretching modes of the trigonal planar BO3 groups. Moreover, intense Raman modes located at 631 cm−1 is related to BO3 bending vibration as well. The weak band at 1158 cm−1 (A1 mode) and strong band at 431 cm−1 (A1 mode) are attributed to asymmetric stretching and bending vibration mode of tetrahedral BO4 groups respectively. The vibrational band at 765–738 cm−1 in the Raman spectra of NVBO crystal maybe related to the breathing vibration of the boroxol ring consisting of two BO4 tetrahedra. In addition, we assigned the intense band 900 (A1 mode) and 831 cm−1 (B2 mode) are relative to the v1 symmetric stretching vibration of VO4 tetrahedra. And the middle intense band at 382 (A1 mode) and 385 (A2 mode) are due to OVO vibration in VO4 tetrahedra.

On the Use of Dynamical Diffraction Theory To Refine Crystal Structure from Electron Diffraction Data: Application to KLa5O5(VO4)2, a Material with Promising Luminescent Properties.

A new lanthanum oxide, KLa5O5(VO4)2, was synthesized using a flux growth technique that involved solid-state reaction under an air atmosphere at 900 °C. The crystal structure was solved and refined using an innovative approach recently established and based on three-dimensional (3D) electron diffraction data, using precession of the electron beam and then validated against Rietveld refinement and denisty functional theory (DFT) calculations. It crystallizes in a monoclinic unit cell with space group C2/m and has unit cell parameters of a = 20.2282(14) Å, b = 5.8639(4) Å, c = 12.6060(9) Å, and β = 117.64(1)°. Its structure is built on Cresnel-like two-dimensional (2D) units (La5O5) of 4*3 (OLa4) tetrahedra, which run parallel to (001) plane, being surrounded by isolated VO4 tetrahedra. Four isolated vanadate groups create channels that host K(+) ions. Substitution of K(+) cations by another alkali metal is possible, going from lithium to rubidium. Li substitution led to a similar phase with a primitive monoclinic unit cell. A complementary selected area electron diffraction (SAED) study highlighted diffuse streaks associated with stacking faults observed on high-resolution electron microscopy (HREM) images of the lithium compound. Finally, preliminary catalytic tests for ethanol oxidation are reported, as well as luminescence evidence. This paper also describes how solid-state chemists can take advantages of recent progresses in electron crystallography, assisted by DFT calculations and powder X-ray diffraction (PXRD) refinements, to propose new structural types with potential applications to the physicist community.

Synthesis and Characterization of Three New Layered Vanadium Tellurites, MVTe2O8 (M = Al, Ga, and Mn): Three-Dimensional (3-D) Antiferromagnetic Behavior of MnVTe2O8 with a Zigzag S = 2 Spin Chain.

Three new metal vanadium tellurites, MVTe2O8 (M = Al, Ga, and Mn) have been synthesized through standard solid-state and hydrothermal reactions. Crystal structure analyses using X-ray diffraction reveal that the isostructural materials exhibit layered structures consisting of MO6, TeO4, and VO4 polyhedra. The corner-sharing of MO6 octahedra results in one-dimensional (1-D) zigzag chains that are further interconnected by tetrameric Te4O12 units and the VO4 tetrahedra to complete a layered structure. Detailed structural analysis suggests that the unit-cell volumes and the very long Te(2)-O(2) bond distances in MVTe2O8 are closely related to the ionic radii of M(3+) cations. Additional characterizations such as ultraviolet-visible light (UV-vis) and infrared spectroscopies, thermogravimetric analyses, and electron paramagnetic resonance measurements were performed. The temperature-dependent magnetic susceptibility measurements on MnVTe2O8 suggest that the material behaves like a three-dimensional (3-D) antiferromagnet with T(N) = 30 K, although the structure consists of a zigzag S = 2 spin chain.

Insertion of Trivalent Lanthanides into Uranyl Vanadate Layers and Frameworks.

Two new uranyl vanadates have been prepared from hydrothermal reactions and structurally characterized by single-crystal X-ray diffraction. The structure of (H3O)UO2VO4 (UVO-1) consists of anionic layers containing UO2(2+) pentagonal bipyramids coordinated by edge-sharing VO5 square pyramids, with the charge balanced by interlaminar H3O(+) cations. Vanadium in (UO2)3(VO4)2(H2O)3 (UVO-2) exists as monomeric VO4 tetrahedra coordinating to UO2(2+) pentagonal bipyramids, forming a 3D uranyl(VI) vanadate framework. Similar reactions with the addition of Ln(NO3)3 (Ln = Nd, Eu) afford the three heterobimetallic lanthanide uranyl vanadate frameworks Nd(UO2)3(VO4)3(H2O)11 (NdUVO-1), Eu(UO2)3(VO4)3(H2O)10 (EuUVO-1), and Eu2(UO2)12(VO4)10(H2O)24 (EuUVO-2). In NdUVO-1 and EuUVO-1, Ln(3+) cations are inserted into the interlayer space of UVO-1 substituting for H3O(+) and further bridging adjacent layers into 3D frameworks. Similarly, EuUVO-2 adopts the same sheet topology as UVO-2, with Eu(3+) ions replacing some of the interlayer uranyl ions in UVO-2. Our work has demonstrated that uranyl vanadate extended structures are excellent hosts for further incorporation of trivalent lanthanide/actinide cations and has provided a new way to create new heterobimetallic 4f-5f and 5f-5f compounds.

Synthesis and crystal structure of Bi6(Bi0.5Cu0.5)V2O15+y

The structure of the oxide with composition Bi6(Bi0.5Cu0.5)V2O15+y has been solved based on single crystal X-ray diffraction and is found to be monoclinic (S. G. I2), a=11.276(1)Å, b=5.4513(2)Å, c=11.055(3)Å, β=96.70°(1). The crystal was twinned by 180° rotoinversion about [1¯ 0 1] in the direct lattice as found in the the phosphates, Bi6TiP2O16 and Bi6+xM1−xP2O15+y (M=Mn, Fe and Ni), wherein chains of edge sharing (OBi4) tetrahedral units are connected by layers of VO4 tetrahedra and (Bi/Cu)O6−x (x=oxygen vacancies) octahedra.

Pressure-induced amorphization of metavanadate crystals SrV2O6 and BaV2O6

Lattice vibrations and electrical transport properties of SrV2O6 (SVO) and BaV2O6 (BVO) under high pressure have been investigated by Raman spectra and alternating current (AC) impedance spectra measurements. A pressure-induced structural phase transition in SVO is observed at 3.9 GPa, and the phase transition in BVO happens at 4.3 GPa from their high-pressure Raman spectra. With further increasing pressures, amorphization is found in both SVO and BVO at 10.1 and 9.3 GPa, respectively. Pressure-induced amorphization of SVO and BVO is suggested to be associated with the breaking up of infinite chains of corner-linked tetrahedral VO4 into VO3−. The recovery of original crystalline phases along with the re-linking of VO3− chains is observed after heating the reclaimed samples. Furthermore, the in situ high pressure measurements of AC impedance spectra of BVO reveal two distinct changes in its resistance, which can correspond to the transitions as observed in the Raman spectra.

Photocatalytic ability of vanadate garnet Ca5Ni4(VO4)6 under visible-light irradiation

A new visible-light-driven photocatalyst was developed in a vanadate garnet Ca5Ni4(VO4)6. The particles were prepared by a modified Pechini method. The sample was characterized with measurements such as x-ray powder diffraction, scanning electron microscope, and UV–vis absorption spectrum. The photocatalytic activities of Ca5Ni4(VO4)6 particles were evaluated by photodegradation of methylene blue under visible-light irradiation in air. Ca5Ni4(VO4)6 shows photocatalytic activity due to an efficient absorption in the UV–visible light wavelength region with a narrowed band gap energy of 2.13 eV and an indirectly allowed electronic transition. These results indicate that this vanadate garnet could be a potential photocatalyst driven by visible-light. The effective photocatalytic activity was discussed on the base of the crystal structure, the photoluminescence and the decay lifetime. The photocatalytic ability of Ca5Ni4(VO4)6 is related to structure characteristics such as the regular and isolated VO4 tetrahedron, the optical centers of Ni–O octahedron, the low opportunity for the recombination of electron–hole pairs in the lattices.

Tunable optical properties of multiphase ZnO–V2O5 polycrystalline powders

Bright yellow and white-yellow light emitting ZnO–V2O5 polycrystalline powders are synthesized by engineering zinc oxide and different zinc vanadate phases. Emission characteristics strongly depend on different zinc vanadate phases. The bright yellow emission is originated from the 3T2→1A1 and 3T1→1A1 transitions in the VO4 tetrahedra of zinc vanadate phase. White-yellow emission is the combination of blue and green emissions due to native point defects of ZnO and the yellow and red emission from zinc vanadate.

Enhancing the Efficiency of Water Oxidation by Boron-Doped BiVO4 under Visible Light: Hole Trapping by BO4 Tetrahedra.

Boron-doped monoclinic and tetragonal phases of BiVO4 were prepared by using the urea precipitation method, and the visible-light photocatalytic activities of pristine and boron-doped BiVO4 for oxygen generation from water were compared. Boron doping enhances the photocatalytic activities of BiVO4 . The reasons for this enhancement were probed by performing X-ray photoelectron, Raman, and electrochemical impedance spectroscopy measurements, and also by performing density functional calculations for model boron-doped BiVO4 structures. The photocatalytic activities of BiVO4 is enhanced by boron doping because the resulting BO4 tetrahedra, which are smaller than the VO4 tetrahedra, create an occupied defect level per boron lying approximately 0.17 eV above the valence-band maximum of pristine BiVO4 , and this defect level is localized because it is made up of the O 2 p levels of the BO4 tetrahedron. Thus, the BO4 tetrahedra that result from boron doping act as hole traps, thereby slowing down the recombination of photogenerated electrons and holes.

Synthesis, structure, and density functional theory study on a dinuclear alkaline earth vanadate oxide compound

A dinuclear polyoxovanadate cluster Sr2V2O7·H2O was synthesized by hydrothermal reaction, and characterized by single-crystal X-ray crystallography, inductively coupled plasma (ICP-AES), and FTIR analysis. Sr2V2O7·H2O crystallizes in the monoclinic space group C 2/c with a = 14.8631(14) A, b = 7.0433(7) A, c = 14.9872(12) A, β = 151.389(4)°, V = 751.30(12) A3, Z = 4, M r = 407.14, D c = 3.599 g cm−3, F(000) = 752, λ(Cu/Kα) = 1.54178 A, μ = 16.537 mm−1, GOOF = 1.092, R 1 = 0.0330 for 850 observed reflections with I > 2σ(I) and wR 2 = 0.0890 for all data. Sr2V2O7·H2O consists of one [V2O7]4− anion, two Sr2+ counter cations and one lattice water. The V2O7 4− anion has two VO4 tetrahedra linked by one µ 2-oxo, other terminal V–O (µ 1-oxo) bonds are all double-bonded. The results of DFT calculation are in agreement with the observation.