VO4 Tetrahedra Research Articles

Synthesis and magnetic properties of a new series of triangular-lattice magnets, Na2BaMV2O8 (M = Ni, Co, and Mn)

A new series of triangular-lattice magnets, Na2BaMV2O8 (M = Ni, Co, and Mn), are reported. These three compounds crystallize with the Ag2BaMnV2O8 type structure, where the magnetic M2+ ions form a two-dimensional triangular lattice. The magnitude of the exchange interactions in these compounds is moderate because the nonmagnetic VO4 tetrahedra interrupt direct connections between MO6 octahedra. The magnetic susceptibilities of Na2BaNiV2O8 and Na2BaCoV2O8 reveal ferromagnetic transitions at 8.4 and 3.9 K, respectively. In contrast, the magnetic susceptibility of Na2BaMnV2O8 exhibits a broad maximum at around 2.3 K, which suggests antiferromagnetic nearest-neighbour interactions and a significant effect of geometric frustration. The specific heat and magnetization curve of Na2BaMnV2O8 indicate that magnetic long-range ordering appears below 1.5 K.

Early‐Lanthanide Complexes with All‐Inorganic Macrocyclic Polyoxovanadate Ligands

AbstractThree discrete early‐lanthanide complexes with cyclic polyoxovanadate ligands, [LaV10O30]7– (1), [CeV9O27]6– (2), and [PrV9O27]6– (3), were synthesized by reaction of [VO3]– with early‐lanthanide(III) salts. Complexes 1–3 were composed of a LnIII center in square‐antiprism coordination mode with coordinated all‐inorganic ligands [VnO3n]n– (n = 9 or 10), which were constructed from a cyclic linkage of nine or ten VO4 tetrahedra through vertex sharing. Structural investigation of lanthanum complex 1 revealed a ten‐membered ring of VO4 units in which eight VO4 units were coordinated to the lanthanum atom through their oxido groups and two VO4 units at opposite sides of the ring were not coordinated. Cerium complex 2 and praseodymium complex 3 both contained a nine‐membered cyclic ligand with eight VO4 coordinated units and one uncoordinated unit among nine tetrahedral VO4 units. 51V NMR spectra of 1–3 in acetonitrile showed reversible temperature dependences at –40–70 °C, thus indicating fluxional behavior of the macrocyclic polyoxovanadate ligands in solution. Exchange of the coordinated and uncoordinated VO4 sites in the ring was responsible for these reversible processes.

Factors affecting the magnetic coupling in Sr2V3O9 type oxides: As for V substitution in the VO4 tetrahedra and nature of the cation

A density functional theory study of the magnetic couplings in Sr2V3O9 type magnetic oxides suggests that whereas the intrachain coupling is always weakly ferromagnetic, the interchain coupling may be antiferromagnetic or even weakly ferromagnetic depending on the nature of the central tetrahedral atom (As/V) cations, and, to a lesser extent, structural details.

Low temperature-synthesis of BiVO4 nanorods using polyethylene glycol as a soft template and the visible-light-activity for copper acetylacetonate decomposition

Monoclinic sheelite BiVO4 nanorods (ms-BiVO4 NRs) have been synthesized from an aqueous solution of Bi(NO3)3 and NH4VO3 at 370K containing polyethylene glycol (PEG), while micron-sized BiVO4 crystals (ms-BiVO4 MCs) are formed without PEG. The UV–vis absorption spectra of the PEG solutions of NH4VO3 suggested the formation of a complex consisting of VO3− ion and PEG. In this synthetic route, PEG can suppress the reactivity of VO3− ions by the stabilization to further act as a soft template for the formation of ms-BiVO4 NRs. The as-grown ms-BiVO4 NRs exhibit a high level of photocatalytic activity for the degradation of Cu(acac)2 without sacrificial agents under illumination of visible-light (λ>430nm). The local symmetry of VO4 tetrahedron affecting the light absorption intensity in addition to the large surface area and high crystallinity have been suggested to be a crucial factor to achieve the high visible-light-activity of ms-BiVO4.

Synthesis, structural and thermal studies of Pu(VO3)4: A new vanadate in PuO2–V2O5 system

A new phase Pu(VO3)4 in PuO2–V2O5 system was prepared by heating an appropriate amount of pre-dried PuO2 and V2O5 at 640°C. The structural and thermal properties of Pu(VO3)4 were investigated by powder X-ray diffraction and thermogravimetry (TG). Structural analyses revealed that Pu(VO3)4 crystallizes in tetragonal (space group: I41/a) lattice with unit cell parameters, a=8.4528(2)Å and c=28.6644(9)Å and is isostructural to metavanadates of thorium and neptunium. Structure shows crystallographically two distinct vanadium atoms V(1) and V(2), one plutonium atom (Pu1) and seven oxygen atoms in the unit cell of Pu(VO3)4. Vanadium atoms form VO4 tetrahedra while plutonium forms PuO8 polyhedra with oxygen atoms. The VO4 units are linked together by sharing apex oxygen atoms and form infinite spiral chains of (VO3)n. Along c-axis, the plutonium atoms are sandwiched between the two layers of (VO3)n chains. TG of Pu(VO3)4 showed thermal stability of the compound up to 700°C.

Flexible and Dynamic Thermal Behavior of Self-Catenated [{Ni3(H2O)3(Bpa)4}(V6O18)]·8H2O Constructed from 10-c Heterometallic Inorganic–Organic Clusters

The hydrothermal treatment of Ni(NO(3))(2)·6H(2)O, NaVO(3), and Bpa (1,2-Di(pyridyl)ethane) (C(12)H(12)N(2)) at 120 °C during 3 days leads to green single crystals of the title compound. The single crystal X-ray diffraction reveals that [{Ni(3)(H(2)O)(3)(Bpa)(4)}(V(6)O(18))]·8H(2)O crystallizes in the monoclinic system, P2(1)/c space group, with a = 13.5536 (2), b = 19.0463 (2), c = 27.7435 (3) Å, β = 112.3880 (10)°, V = 6622(3) Å(3), with R1(obs) = 0.0558, wR2(obs) = 0.1359, for 10278 observed reflections. The complexity of the crystal structure is based on different points, as the existence of: both "gauche" and "trans" conformations of the organic ligand, the [V(12)O(36)](-12) cycles, formed by 12 corner-sharing VO(4) tetrahedra, and, finally, the combination of both three-dimensional metal-organic and inorganic substructures, giving rise to a self-catenated highly connected net. The crystallization water molecules are semi-encapsulated in the channels along the [100] direction, and their loss gives rise to a dynamical and reversible structural contraction. Moreover, after the removal of the crystallization water molecules, the compound exhibits a negative thermal behavior in the 85-155 °C temperature range, and irreversible structural transformation due to the loss of coordinated water molecules up to 200 °C. The IR and UV-vis spectra were determined for the as-synthesized sample, after the removal of crystallization water molecules and after the irreversible transformation due to the loss of coordinated water molecules. The thermal evolution of χ(m) was adjusted to a magnetic model considering an isotropic dimer plus two Ni(II) d(8) isolated octahedra.

Superposition of ferromagnetic and antiferromagnetic spin chains in the quantum magnet BaAg2Cu[VO4]2

Based on density functional theory band structure calculations, quantum Monte-Carlo simulations, and high-field magnetization measurements, we address the microscopic magnetic model of BaAg2Cu[VO4]2 that was recently proposed as a spin-1/2 anisotropic triangular lattice system. We show that the actual physics of this compound is determined by a peculiar superposition of ferromagnetic and antiferromagnetic uniform spin chains with nearest-neighbor exchange couplings of Ja(1) ~ -19 K and Ja(2) ~ 9.5 K, respectively. The two chains featuring different types of the magnetic exchange perfectly mimic the specific heat of a triangular spin lattice, while leaving a clear imprint on the magnetization curve that is incompatible with the triangular-lattice model. Both ferromagnetic and antiferromagnetic spin chains run along the crystallographic 'a' direction, and slightly differ in the mutual arrangement of the magnetic CuO4 plaquettes and non-magnetic VO4 tetrahedra. These subtle structural details are, therefore, crucial for the ferromagnetic or antiferromagnetic nature of the exchange couplings, and put forward the importance of comprehensive microscopic modeling for a proper understanding of quantum spin systems in transition-metal compounds.

Enhancement of the visible light absorption intensity of microporous vanadosilicate AM-6

AM-6 with high intensity visible light absorption at 400-800 nm was synthesized via a hydrothermal route in the presence of F(-) ions. Structure characterization and DFT calculations indicate that the unusual optical properties originate from the connection of octahedral VO(6) wires with distorted tetrahedral VO(4) units, which are stabilized in the framework of AM-6.

Roles of Bi, M and VO4 tetrahedron in photocatalytic properties of novel Bi0.5M0.5VO4 (M=La, Eu, Sm and Y) solid solutions for overall water splitting

Novel Bi0.5M0.5VO4 (BMV; M=La, Eu, Sm and Y) solid solutions were prepared and studied in this paper. All the samples were proved to produce H2 and O2 simultaneously from pure water under the irradiation of UV light. M–O bond lengths were proved to increase with M cations by refining cell parameters and atomic positions. Besides, band gaps, energy gaps and photocatalytic activities of BMV also changed with M cations. Both of M–O and V–O bond lengths were suggested to account for this phenomenon. Inactive A0.5Y0.5VO4 (A=La, Ce) for water splitting proved incorporation of Bi rather than distortion of VO4 tetrahedron was a critical factor for improving efficiency of overall water splitting by facilitating the generation of electron and hole with lighter effective masses. Replacement of Bi by M cations not only gave indirect effect on band structure but also raised position of conduction band minimum to meet requirement of H2 production.

Electrical conductivity and local structure of barium manganese iron vanadate glass

Local structure and electrical conductivity of semiconducting 20BaO·10Fe2O3·x MnO2·(70 − x)V2O5 glass (x = 0 − 30), abbreviated as xBFMV, were investigated by means of 57Fe-Mossbauer spectroscopy, differential thermal analysis (DTA) and DC four-probe method. Mossbauer spectrum of these vanadate glasses consists of a doublet with an identical isomer shift (δ) of 0.38±0.01 mm s − 1, indicating that distorted FeO4 tetrahedra constitute the structural units with distorted VO4 tetrahedra and VO5 pyramids. Quadrupole splitting (Δ) gradually increases from 0.70±0.02 to 0.87±0.02 mm s − 1 with an increase in the MnO2 content, indicating an increased local distortion of FeIIIO4 tetrahedra. DTA study of these glasses showed a gradual increase of glass transition temperature (T g) from 329±5 to 411±5°C, showing an improved thermal durability. ‘T g vs. Δ plot’ yielded a straight line with a large slope of 707°C(K)/mm s − 1, proving that FeIII played a role of network former (NWF). An isothermal annealing of 10BFMV glass at 500°C for 1000 min resulted in a marked increase in the electrical conductivity (σ) from (4.5±3.9) × 10 − 7 to (1.4±0.3) × 10 − 2 S cm − 1 and a decrease in the activation energy for the electrical conduction (E a) from 0.33 ± 0.07 to 0.11±0.01 eV, while Δ of FeIII decreased from 0.76±0.02 to 0.49±0.02 mm s − 1. These results suggest that decrease in the distortion of FeIIIO4 tetrahedra involved with the structural relaxation causes an increase in the probability of electron hopping from VIV or VIII to VV.

Structural and electrical studies of LiMnVO4 cathode material for rechargeable lithium batteries

The lithium manganese vanadate (LiMnVO4) cathode material was synthesized by using sol–gel method. The thermal behavior of the material has been examined by thermogravimetric and differential thermal analysis. The structure of LiMnVO4 compound was studied by the Rietveld refined X-ray diffraction technique. Raman spectra showed that the local environment including VO4 tetrahedra and LiO6 octahedra as vibrational local units. X-ray photoelectron spectroscopy studies of synthesized LiMnVO4 powder indicate that the oxidation states of manganese and vanadate are +2 and +5, respectively. The ionic conductivity of the sample is found to be 2.7 × 10−5 Scm−1 at 300 °C. The temperature dependent conductivity was conformed from the Arrhenius relation and the activation energy is found to be 0.3 eV. Dielectric spectra showed the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the compound.

バナジナイトPb5(VO4)3Clの構造の再検討、特にVO4四面体の秤動とClの異方性温度因子について

バナジナイトPb5(VO4)3Clの構造の再検討、特にVO4四面体の秤動とClの異方性温度因子について

Synthesis and study of compounds of the general formula MITh2(VO4)3 (MI = Li, Na, Ag, K, Rb, Cs, Tl)

Double vanadates of thorium and univalent metals with r(MI) < 1.6 A were prepared by high-temperature solid-phase reactions. Representatives of this series with larger MI atoms were prepared by the solgel method. The compounds crystallize in three structural types: zircon for Li and Na derivatives, scheelite for AgTh2(VO4)3, and potassium thorium vanadate for the compounds containing K, Rb, Cs, and Tl. Thus, two morphotropic transitions are observed in the series of the compounds studied. The bands in the IR spectra were assigned, and the effect of the site symmetry of the VO4 tetrahedra on the number of absorption bands was revealed. The incongruent melting points of the compounds were determined by differential scanning calorimetry.

Magnetic Properties of Monomer and Dimer Tetrahedral VO(x) Entities Dispersed on Amorphous Silica-based Materials: Prediction of EPR Parameters from Relativistic DFT Calculations and Broken Symmetry Approach to Exchange Couplings.

Molecular structures of the isolated tetrahedral oxovanadium(IV) and bridged μ-oxo-divanadium(IV) complexes hosted by the clusters mimicking surfaces of amorphous silica-based materials were investigated using density functional theory (DFT) calculations. Principal values of the g and A tensors for the monomer vanadyl species were obtained using the coupled-perturbed DFT level of theory and the spin–orbit mean-field approximation (SOMF). Magnetic exchange interaction for the μ-oxo bridged vanadium(IV) dimer was investigated within the broken symmetry approach. An antiferromagnetic coupling of the individual magnetic moments of the vanadium(IV) centers in the [VO–O–VO]2+ bridges was revealed and discussed in detail. The coupling explains pronounced decrease of the electron paramagnetic resonance signal (EPR) intensity, observed for the reduced VOx/SiO2 samples with the increasing coverage of vanadia, in terms of transformation of the paramagnetic monomer species into the dimers with S = 0 ground state.

Synthesis and structure of A4V6[Te24+Te6+]O24 (A = K, Rb)—two new quaternary mixed-valent tellurium oxides

Two new mixed-valent tellurium oxides with vanadium(V), A(4)V(6)[Te(2)(4+)Te(6+)]O(24) (A = K and Rb), have been synthesized by hydrothermal and conventional solid state techniques. Their structures were determined by single-crystal X-ray diffraction analysis. These two iso-structural compounds exhibit layered structural topologies consisting of [V(6)Te(3)O(24)](4-) anionic units. In these anionic structural units, a Te(6+)O(6) octahedron is connected to six VO(4) tetrahedra by corner-sharing to generate a [V(6)TeO(24)] unit, and each of these [V(6)TeO(24)] units are interconnected by sharing two Te(4+)O(3) polyhedra to complete the infinite [V(6)Te(3)O(24)](4-) sheets. Infrared spectroscopy, UV-Visible diffuse reflectance spectroscopy, and thermogravimetric analysis were also performed on these two compounds. Crystal data: K(4)V(6)Te(3)O(24), trigonal, space group R ̅3c (No. 167) with a = b = 9.7075(6) Å, c = 42.701(3) Å, V = 3484.9(4) Å(3), and Z = 6; Rb(4)V(6)Te(3)O(24), trigonal, space group R ̅3c (No. 167) with a = b = 9.8399(9) Å, c = 43.012(4) Å, V = 3606.6(6) Å(3), and Z = 6.

Covalently interconnected and separated vanadosilicate shells

ABSTRACTFour new compounds containing vanadosilicate clusters have been synthesized by hydrothermal reactions. The clusters are derived from the [V18O42] Keggin cluster by substitution of V=O caps by Si2O(O,OH)2 species. In Cs9[(V15Si6O46(OH)2Cl)(V2O4)](H2O)6.2, 1, the [V15Si6O46(OH)2] cluster shells are covalently interconnected by VO4 tetrahedra to form an infinite layer. In ((CH3)4N)4[V15Si6O42(OH)6(H2O)](H2O)20, 2, and ((CH3)4N)4(V(H2O)6)2/3 [V15Si6O42(OH)6 (H2O)](H2O), 3, separated [V15Si6O42(OH)6] cluster shells are interlinked by hydrogen bonds to form frameworks with wide channel systems. The separated cluster shell in ((CH3)4N)4((CH3)2NH2)((CH3)2NH) [V14Si8O42(OH)8(HCO2)] (H2O)4.7, 4, has four Si2O(OH)2 species in a tetrahedral configuration. The 2D structure of 1 and 0D structures of 2-4 complement the known 1D and 3D structures formed from such vanadosilicate shells.

β-Cu2V2O7: A spin-12honeycomb lattice system

We report on band structure calculations and a microscopic model of the low-dimensional magnet beta-Cu2V2O7. Magnetic properties of this compound can be described by a spin-1/2 anisotropic honeycomb lattice model with the averaged coupling \bar J1=60-66 K. The low symmetry of the crystal structure leads to two inequivalent couplings J1 and J1', but this weak spatial anisotropy does not affect the essential physics of the honeycomb spin lattice. The structural realization of the honeycomb lattice is highly non-trivial: the leading interactions J1 and J1' run via double bridges of VO4 tetrahedra between spatially separated Cu atoms, while the interactions between structural nearest neighbors are negligible. The non-negligible inter-plane coupling Jperp~15 K gives rise to the long-range magnetic ordering at TN~26 K. Our model simulations improve the fit of the magnetic susceptibility data, compared to the previously assumed spin-chain models. Additionally, the simulated ordering temperature of 27 K is in remarkable agreement with the experiment. Our study evaluates beta-Cu2V2O7 as the best available experimental realization of the spin-1/2 Heisenberg model on the honeycomb lattice. We also provide an instructive comparison of different band structure codes and computational approaches to the evaluation of exchange couplings in magnetic insulators.

Cd1−xBix(Cd1+xIn1−x)VO6 (0 ≤ x ≤ 0.14): A New Polar Oxide with Second-Harmonic Generation

The structure of the new polar oxide, Cd2InVO6, was determined by powder X-ray diffraction. Cd2InVO6 crystallizes in space group P31 with the unit cell parameters: a = 12.218 96(4), c = 9.256 75(4) A. The Cd2+ and In3+ ions are statistically disordered in nine independent positions (M1−M9) with a certain level of site preference. M1−M3 form highly asymmetric oxygen-coordination polyhedra, which are similar to those formed by alkali or alkali-earth cations. M4−M9 are in distorted octahedral cavities. It is shown that M1−M3 are likely occupied mostly by Cd2+ while M4−M9 are extensively mixed by Cd2+ and In3+. The structure is best described as a framework of interconnected M4−M9 distorted octahedra with the M1−M3 polyhedra off-framework and the three independent VO4 tetrahedra filling the channels of the framework structure by corner-sharing with the MO6 octahedra. The polar framework is composed of M4O6∼M9O6 octahedra in a five-connected net with the topology nomination (33, 63, 94). The Bi3+-substituted c...

Correlation between Luminescence Quantum Efficiency and Structural Properties of Vanadate Phosphors with Chained, Dimerized, and Isolated VO4 Tetrahedra

The internal luminescence quantum efficiency and color properties of AVO3 (A: Li, Na, K, Rb, and Cs), M2V2O7 (M: Mg, Ca, Sr, Ba, and Zn), and M3V2O8 (M: Mg, Ca, Sr, Ba, and Zn) have been investigated. These vanadate phosphors exhibited broadband emission from 400 nm to over 800 nm due to the one-electron charge transfer transition in the VO4 tetrahedra, and the color of the luminescent materials ranged from green to yellow-orange via white, corresponding to 0.277 < x < 0.494 and 0.389 < y < 0.488 on the CIE chromaticity diagram. We found that the luminescence quantum efficiency of the vanadate phosphors with VO4 tetrahedra was strongly enhanced by the strong interaction between V ions and the weak interaction between V and A(M) ions in the crystal structures. We hypothesize that the long exciton diffusion lifetime induced by these structural features enhanced luminescence, leading to high quantum efficiency.

Effect of thermal transformations of constituent polyhedra of the crystal structure on the properties of Cd2V2O7

Analysis of variations in the linear and angular parameters of constituent polyhedra of the cadmium pyrovanadate Cd2V2O7 structure, namely, VO4 tetrahedra and CdO6 octahedra, as calculated from the results of in situ high-temperature X-ray diffraction experiments in the range from 25 to 900°C, showed that, in the range from 600 to 720°C, the thermal expansion coefficient (tec) of CdO6 polyhedra is near zero, whereas VO4 tetrahedra increase in volume, although less strongly than in other temperature ranges. A structural interpretation is given to anomalous temperature dependences of cadmium ion emission and electrical conductivity on the basis of different thermal behavior patterns of the constituent polyhedra of the Cd2V2O7 structure.