New organic–inorganic hybrid structure based on paradodecatungstate clusters and imidazolium cations

An organic–inorganic hybrid material based on paradodecatungstate anions and imidazolium cations, Na₂(HIm)₈(H₂W₁₂O₄₂)·10H₂O (HIm: imidazolium), has been synthesized under mildly acidic conditions. This compound was characterized by single-crystal X-ray diffraction, IR and UV–visible spectroscopies, and thermogravimetric and differential thermal analyses. The compound crystallizes in the triclinic P-1 space group with a = 11.6945(8) Å, b = 12.4782(6) Å, c = 14.0952(9) Å, α = 106.041(3)°, β = 109.338(2)°, γ = 100.249(3)°, V = 1781.0(3) Å³, and Z = 2. The crystal structure exhibits an infinite 1D inorganic structure built from [H₂W₁₂O₄₂]^10? clusters and sodium cations; adjacent chains are further joined up by hydrogen-bonding interactions between protonated imidazole cations, water molecules, and polyoxoanions, to form a 3D supramolecular architecture.     

V2O2F4(H2O)2·H2O: a new V4+ layer structure related to VOF3

V^IV oxyfluorides are of interest as frustrated magnets. The successful synthesis of two‐dimensionally connected vanadium(IV) oxyfluoride structures generally requires the use of ionic liquids as solvents. During solvothermal synthesis experiments aimed at producing two‐ and three‐dimensional vanadium(IV) selenites with triangular lattices, the title compound, diaquatetra‐μ‐fluorido‐dioxidodivanadium(IV) monohydrate, V₂O₂F₄(H₂O)₂·H₂O, was discovered and features a new infinite V⁴⁺‐containing two‐dimensional layer comprised of fluorine‐bridged corner‐ and edge‐sharing VOF₄(H₂O) octahedral building units. The synthesis was carried out under solvothermal conditions. The V⁴⁺ centre exhibits a typical off‐centring, with a short V=O bond and an elongated trans‐V—F bond. Hydrogen‐bonded water molecules occur between the layers. The structure is related to previously reported vanadium oxyfluoride structures, in particular, the same layer topology is seen in VOF₃.     

Neutron diffraction study, magnetism and magnetotransport of stoichiometric CaVO3 perovskite with positive magnetoresistance

A stoichiometric calcium vanadium (IV) oxide with formula CaVO₃ has been prepared by soft-chemistry procedures, followed by annealing under reducing conditions (H₂/N₂ flow). This material has been studied by X-ray and neutron powder diffraction (NPD), thermal analysis, magnetic and magnetotransport measurements. CaVO_3.0 perovskite crystallizes in the orthorhombic Pbnm (No. 57) space group, with the GdFeO₃-type structure. The unit-cell parameters are , and . In this distorted perovskite the VO₆ octahedra are tilted by 10.1° in order to optimize the Ca-O bond-lengths. A bond valence study from NPD data confirms the tetravalent oxidation state for V cations. The perovskite is fully oxygen stoichiometric, as demonstrated from thermal analysis and the refinement of the oxygen occupancy factors. The magnetic susceptibility is predominantly Pauli paramagnetic-like, although a non-negligible temperature-dependent component due to isolated V⁴⁺ spins is patent at low temperatures. The transport measurements show a metallic behavior between 2 and 300 K; at low temperatures a positive magnetoresistance as large as 14% for H=9 T is interpreted as the result of quantum interference effects.     

Synthesis and structure investigation of the Pb3V(PO4)3 eulytite

Lead vanadium phosphate Pb₃V(PO₄)₃ was synthesized by solid state reaction and characterized by X-ray single crystal and powder diffraction, electron microscopy, and magnetic susceptibility measurements. The crystal structure model of Pb₃V(PO₄)₃ was refined using X-ray single crystal data (a=10.127(1)Å, S.G. Z=4). The compound has an eulytite-like structure and its average structure model may be presented as a three-dimensional network formed by strongly distorted mixed (Pb/V^III) metal-oxygen octahedra connected by edge sharing and forming corrugated chains. The octahedra are additionally linked by tetrahedral phosphate groups via corner sharing. Lead and vanadium atoms randomly occupy two close positions in the octahedra. The electron microscopy study revealed the presence of a rhombohedral superstructure with and indicating ordering in the structure. The same type of superstructure was found by us for two another lead-containing eulytite Pb₃Fe(PO₄)₃ where Fe⁺³ has an ionic radius close to that of V⁺³. Magnetic susceptibility measurements revealed Curie-Weiss behavior for the Pb₃V(PO₄)₃ compound.     

Syntheses and crystal structures of the first organically templated metal tellurites

The first organically templated vanadium tellurites, [H₂en][(VO₂)(TeO₃)]₂·H₂O (1, en=ethylenediamine) and [H₂pip][(VO₂)(TeO₃)]₂ (2, pip=piperazine) have been synthesized by hydrothermal reactions and structurally characterized. Both compounds feature a [(VO₂)(TeO₃)]⁻ anionic layer containing V₂Te₂ four-member rings and V₄Te₄ eight member rings. The vanadium (V) atom is five coordinated by three tellurite oxygens and two terminal oxygen atoms in a distorted trigonal bipyramidal geometry. The interconnection of the VO₅ polyhedra by bridging tellurite groups leads to a 2D corrugated anionic inorganic layer. The doubly protonated template cations and the lattice water molecules in 1 are located at the interlayer space and are involved in hydrogen bonding. The doubly protonated template cation in 2 is not involved in hydrogen bonding with the anionic inorganic layer.     

Preparation and characterization of novel alkylviologens-intercalated vanadyl-vanadate (RV)V3O8

Various n-alkylviologens-intercalated vanadyl-vanadate (RV)V₃O₈ were synthesized with the combination of redox and ions-exchange methods. The derivative compounds were characterized by X-ray diffraction (XRD), FT infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The XRD results indicate that the interlayer spacing increases with the alkyl chain length of the alkylviologen cations. The FTIR data shows that alkylviologens were inserted into the interlayers of V₃O₈²⁻. XPS data reveals that the vanadium ions in the intercalation compounds are mostly in a pentavalent V⁵⁺ state with some partially reduced to the V⁴⁺ state. The intercalation compounds have the strong absorption character in the ultraviolet and visible light region. Magnetic susceptibility indicates that the (ethylviologen) V₃O₈ (EV3) is antiferromagnetic and possesses an ordered magnetic structure below 15 K. Above 15 K, EV3 exhibits paramagnetic behavior and a disordered magnetic structure.     

The first transition metal iodato peroxido complex: the synthesis, vibrational spectra and crystal structure from powder diffraction data of K3[V2O2(O2)4(IO3)]·H2O

The first transition metal iodato peroxido complex, K₃[V₂O₂(O₂)₄(IO₃)]·H₂O (I), was prepared by crystallization from the KVO₃ — KIO₃ — H₂O₂ — H₂O — ethanol (HNO₃) solution. The dinuclear anion is immediately decomposed in aqueous solution; the ⁵¹V NMR spectrum exhibits signals corresponding to [VO(O₂)₂(H₂O)]^?, [V₂O₂(OH)(O₂)₄]^3? and H₂VO₄ ^? species only. The IR and Raman spectra contain all characteristic bands of the VO(O₂)₂ group and the coordinated IO₃ ^? ligand. Based on the positions of bands assigned to the vibrations of the VO(O₂)₂ groups a pentagonal pyramidal arrangement around the vanadium atoms can be supposed. The crystal structure was solved from X-ray synchrotron powder data by direct space method and refined by energy minimization in the solid state employing a hybrid PBE0 functional. This crystal and molecular structure, has confirmed the presence of hexacoordinated vanadium atoms and revealed asymmetric dinuclear structure of the [V₂O₂(O₂)₄(IO₃)]^3? ion. The coordination spheres of vanadium atoms are different — the IO₃ ^? anion is coordinated only to one vanadium center. A thermal analysis of the complex confirmed the presence of water molecules in the crystal structure and revealed a considerable stability of the dehydrated complex.      

Theoretical and Experimental Studies of the Nature of the Catalytic Activity of VO x /TiO2 Systems

The states of supported vanadium and the nature of activation of ammonia adsorbed on vanadium sites of V _x /Ti₂ catalysts are studied by ⁵¹V NMR spectroscopy and diffuse-reflectance IR Fourier-transform (DRIFT) spectroscopy using cluster quantum chemical calculations of N₃ adsorption. We employ the V _x /Ti₂ catalyst of two types: the monolayer catalyst in which vanadium is located on the surface of well-crystallized anatase and the catalyst in which vanadium embedded in the anatase lattice at a rather great depth. It is shown that ammonia is predominantly adsorbed on Lewis acid sites of the monolayer catalyst, whereas most of N₃ adsorbed on the catalyst containing bulk vanadium is in the form of ammonium ions. Analysis of experimental and calculated data suggests that, in the monolayer catalyst, N₃ molecules in the selective reduction of nitrogen oxides are activated on Lewis acid sites. Ammonia activation involves the dissociation of the N–H bond in a coordinated molecule, which results in the formation of the amide V–N₂ group and a water molecule coordinated by a V⁵⁺ ion. It is likely that, in the case of the catalyst containing bulk vanadium, this reaction occurs with the predominant participation of ammonium ions.     

Organically Templated Vanadium Oxide Phases: Synthesis and Structures of [H3NCH2CH2NH3][V2O6] and [HN(CH2CH2)3NH][VV2VIV4O14]·H2O

The synthesis and crystal structures of [H₃NCH₂CH₂NH₃][V₂O₆] (1) and [HN(CH₂CH₂)₃NH][V^V ₂V^IV ₄O₁₄]·H₂O (2) are described. The structure of the oxidized compound 1 consists of parallel stacks of vanadium oxide chains of corner sharing {VO₄} tetrahedra. The chains are stabilized by extensive hydrogen bonding involving oxide ligands of the chains and ethylenediammonium ions which fill the space between the stacks of chains. The structure of compound 2 consists of vanadium oxide layers separated by doubly protonated 1,4-diazabicyclo[2.2.2]octane and lattice water. The vanadium oxide layers, containing mixed-valence vanadium (V^V and V^IV) centers, are composed of zigzag ribbons of edge-sharing {VO₅} square pyramids interconnected by {VO₄} tetrahedra. Crystal data. C₂H₁₀N₂O₆V₂ , 1: monoclinic, space group P2₁/c (No. 14), a=5.5359(5), b=12.9430(12), c=5.6856(5) Å, =90, =97.460(2), =90°, V=403.93(6) ų, Z=2. A total of 2506 reflections ( _max=27.89°) was collected, of which 954 were used to resolve the structure. The structure was solved by direct methods and least-squares refinement converged at R=0.0592. C₆H₁₆N₂O₁₅V₆, 2: monoclinic, space group C2 (No. 5), a=19.303(4), b=6.667(2), c=7.579(2) Å, =90, =111.31(2), =90°, V=908.4(4) ų, Z=2. A total of 1779 reflections was collected, of which 1591 unique reflections were used for structural elucidation. The structure was solved by direct methods and least-squares refinement converged at R=0.0314.     

The first tin(II) vanadium(III) phosphate SnVPO5: Crystal structure and magnetic properties

The first tin vanadium phosphate SnVPO₅ was synthesized by a solid-state reaction and characterized by X-ray single crystal diffraction and magnetic susceptibility measurements. The crystal structure of SnVPO₅ (, , , α=113.283(11)°, β=108.037(9)°, γ=94.603(9)°, S.G. P-1, Z=2) is a three-dimensional framework constructed by V₂O₁₀ units fasten together by tetrahedral phosphate groups. Tin atoms are situated in structure interstices. They have five-fold coordination arrangement due to a presence of sterically active lone pair which position was visualized by ELF calculations. The magnetic susceptibility shows a broad maximum at 22 K which is probably due to low-dimensional spin correlations. We propose that the magnetism of the compound can be understood by interacting spin-dimers on a distorted square lattice. Strong quantum fluctuations were suggested by unusual field dependence of the transition temperature and unexpectedly low Curie constant.     

Ultrasound‐Assisted Synthesis of Hybrid Vanadium Oxide/Polyaniline Nanowires

A single‐step sonochemical procedure to synthesize hybrid vanadium oxide/polyaniline nanowires starting from crystalline V₂O₅ and aniline in aqueous medium is presented. The synthesis explores the effect of high power ultrasounds on heterogeneous solid–aqueous phases, which leads to 30 nm width wires of 5 to 10 µm in length. Monomer intercalation and oxidative polymerization within the inorganic matrix proceed simultaneously with morphological changes. The electronic conductivity of hybrid nanowires reaches 0.8 S · cm⁻¹ at room temperature.

     

The synthesis and crystal structure of vanadium complexes: [VO2(phen)2]·6H2O and [2,2′-(bipy)2VO2](H2BO3)·3H2O

The organic-inorganic hybrid materials vanadium oxide [V^IVO₂(phen)₂]·6H₂O (1) and [(2,2′-bipy)₂V^VO₂](H₂BO₃)·3H₂O (2) have been conventional and hydrothermal synthesized and characterized by single crystal X-ray diffraction, elemental analyses, respectively. Although the method and the ligand had been used in the syntheses of the compounds (1) and (2) are different, they almost possess similar structure. They all exhibit the distorted octahedral [VO₂N₄] unit with organonitrogen donors of the phen and 2,2′-bipy ligands, respectively, which coordinated directly to the vanadium oxide framework. And they are both non-mixed-valence complexes. But the compound (1) is isolated, and the compound (2) consists of a cation of [(2,2′-bipy)₂V^VO₂]⁺ and an anion of (H₂BO₃)⁻. So the valence of vanadium of (1) and (2) are tetravalence and pentavalence, respectively. Meanwhile it is noteworthy that π-π stacking interaction between adjacent phen and 2,2′-bipy groups in compounds 1 and 2 also play a significant role in stabilization of the structure. Thus, the structure of [V^IVO₂(phen)₂]·6H₂O and [(2,2′-bipy)₂V^VO₂](H₂BO₃)·3H₂O are both further extended into interesting three-dimensional supramolecular. Crystal data: (1) Triclinic, a=8.481(4), b=12.097(5), and α=66.32(2), β=82.97(3), and γ=82.59(4)°, Z=2, R₁=0.0685, wR₂=0.1522. (2) Triclinic, a=6.643(13), b=11.794(2), and α=101.39(3), β=101.59(3), and γ=97.15(3)°, Z=2, R₁=0.0736, wR₂=0.1998.     

Crystal growth and anisotropic magnetic properties of V3O7

Needle-like crystals of V₃O₇ up to 2 mm in length were grown by a chemical vapor transport method using NH₄Cl as a transport agent. The anisotropic magnetic susceptibility was measured for the first time. At 2 K, a spin-flop transition occurs under a magnetic field of 0.1 T. V₃O₇ is proved to be a uniaxial antiferromagnet with its easy axis parallel to the b-axis of monoclinic structure. A spin structure with antiferromagnetic interaction between layers and ferromagnetic interaction in the layers below the Néel temperature (5.2 K) is suggested.     

The actual structure of K6(VO)2(V2O3)2(PO4)4(P2O7): Ordered distribution of P2O7 groups and charge ordering of vanadium

The actual structure of the vanadium phosphate K₆(VO)₂(V₂O₃)₂(PO₄)₄(P₂O₇) has been determined, using a much larger single crystal than previously used for the isostructural Rb-phase. The actual supercell is four times larger than the corresponding orthorhombic subcell with , , , α=β=γ=90°. The structure resolution, performed in the triclinic space group C-1, shows that the P₂O₇ groups alone are responsible for the superstructure, all the other atoms keeping the atomic positions of the orthorhombic subcell. This structural study shows a perfect ordering of the P₂O₇ groups in the actual structure, in contrast to the results obtained from the subcell. Concomitantly, the V⁴⁺ and V⁵⁺ are found to be ordered in the form of [110] stripes.     

Crystal structure and magnetic properties of hybrid materials self-assembled from the tetrakis(isothiocyanate)cobaltate(II) anion and trisubstituted benzyltriphenylphosphinium

A new hybrid material [BiF4BrBzTPP]₂[Co(NCS)₄] (1) (BiF4BrBzTPP⁺ = 2,6-bisfluoro-4-bromobenzyl-triphenylphosphinium, NCS^? = isothiocyanate) is synthesized and characterized by elemental analyses, IR, UV spectra, ESI-MS, molar conductivity, single crystal X-ray diffraction and magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group C2/c with a = 15.272(2) Å, b = 24.779(3) Å, c = 14.482(2) Å, β = 101.037(2)°, V = 5378.9(12) ų, Z = 4. The compound comprises two cations and one anion which exhibits a distorted tetrahedral coordination geometry. The short F...F, C...Br, and N...Br interactions and C-H...S hydrogen bonds consolidate the stacking of the molecules. Magnetic susceptibility measurements in the temperature range 2–300 K show that 1 exhibits weak antiferromagnetic coupling behavior.     

Phase formation in the system Zn(VO<Subscript>3</Subscript>)<Subscript>2</Subscript>–HCl–VOCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

The phase and chemical compositions of precipitates formed in the system Zn(VO₃)₂–HCl–VOCl₂–H₂O at pH 1?3, molar ratio V⁴⁺: V⁵⁺ = 0.1?9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V⁴⁺: V⁵⁺ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula Zn_xV⁴⁺ _yV⁵⁺ _2-yO₅ ? nH₂O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5?1.2). Vanadate Zn_xV₂O₅ ? nH₂O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V⁴⁺: V⁵⁺ = 1.5?9.0. Investigation of the kinetics of the formation of Zn_xV₂O₅ ? nH₂O at pH 3 determined that tetravalent vanadium ions VO2+ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl₂ can be used as a precursor for producing V₃O₇ ? H₂O nanorods 50–100 nm in diameter.     

Hydrothermal Synthesis and Structural Characterization of a Tubular Arsenic-Vanadate: [CoII(2,2′-bpy)2]2[AsIII8VIV14O42(H2O)]·H2O

The hydrothermal reaction of VOSO₄, As₂O₃, CoC₂O₄·2H₂O and 2,2-bipy yields a novel arsenic-vanadate [Co^II(2,2-bpy)₂]₂[As^III₈V^IV ₁₄O₄₂(H₂O)]·H₂O (1), which is characterized by IR, elemental analysis, TGA, magnetic susceptibility and single crystal X-ray diffraction analysis. X-ray diffraction shows that compound 1 is the first example of tubular arsenic–vanadium cluster containing infinite {[Co(2,2-bpy)₂]₂[As₈V₁₄O₄₂(H₂O)]} chain constructed from [As₈V₁₄O₄₂(H₂O)] clusters interconnected through [Co(2,2-bpy)]²⁺ units. Crystal data: 1, orthorhombic, P 2₁2₁2₁, a=12.1401(2) Å, b=15.8722(1) Å, c=39.9533(5) Å, Z=4.Graphical Abstract: A novel polyoxoarsenicvanadate, [Co^II(2,2-bipy)₂]₂ [As^III₈V^IV ₁₄O₄₂(H₂O)]·H₂O, is depicted along with a tubular hybrid solid with a rhombic tube formed within the chain.     

Synthesis,structure and the e.s.r. spectrum of the mixed-valence molybdovandate Na2(NH4)4[(VIVVV8Mo)O28] · 10H2O

The mixed-valence molybdovanadate compound Na₂(NH₄)₄[V^IVV^V ₈Mo)O₂₈] · 10H₂O [Vanadata(6-)tetradeca--oxotetra-₃-oxodi-₆-oxoheptaoxo(oxomolybdate) nonatetrammonium disodium, decahydrate] has been synthesized from sodium molybdate(VI) dihydrate and sodium metavanadate dihydrate in aqueous solution by adding NH₂OH · HCl. The molecular structure has been determined by X-ray diffraction and is based on the isopolydecavanadate structure. The molybdate atom is crystallographically disordered over 6MO₆ octahedral sites. The e.s.r. spectrum clearly indicates that one vanadium atom has the oxidation number +4.     

Investigations of vanadium oxide bronzes θ-(Fe1−yAly)xV2O5

The vanadium oxide bronzes θ-(Fe_1?yAl_y)_xV₂O₅ are Curie-Weiss paramagnets and hopping semiconductors. The samples studied were synthesized by direct solid-state reaction and investigated by the X-ray diffraction, differential thermal analysis, electrical resistivity, magnetic susceptibility, and Mössbauer techniques. The crystal lattice parameters, effective magnetic moments of Fe³⁺ cations, Curie-Weiss temperatures, and the values of ⁵⁷Fe hyperfine interaction parameters were determined. Endothermic effects were observed for some of the samples.     

Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

The crystal structure of V_0.985Al_0.015O₂ has been refined from single-crystal X-ray data at four temperatures. At 373°K it has the tetragonal rutile structure. At 323°K, which is below the first metal-insulator transition, it has the monoclinic M₂ structure, where half of the vanadium atoms are paired with alternating short (2.540 Å) and long (3.261 Å) V-V separations. The other half of the vanadium atoms form equally spaced (2.935 Å) zigzag V chains. At 298°K, which is below the second electric and magnetic transition, V_0.985Al_0.015O₂ has the triclinic T structure where both vanadium chains contain V-V bonds, V(1)-V(1) = 2.547 Å and V(2)-V(2) = 2.819 Å. At 173°K the pairing of the V(1) chain remains constant: V(1)-V(1) = 2.545 Å, whereas that of the V(2) chain decreases: V(2)-V(2) = 2.747 Å. From the variation of the lattice parameters as a function of temperature it seems that these two short V-V distances will not become equal at lower temperatures. The effective charges as calculated from the bond strengths at 298 and 173°K show that a cation disproportionation has taken place between these two temperatures. About 20% of the V⁴⁺ cations of the V(1) chains have become V³⁺ and correspondingly 20% of the V⁴⁺ cations of the V(2) chains have become V⁵⁺. This disproportionation process would explain the difference between the two short V-V distances. Also it would explain why the T → M₁ transition does not take at lower temperatures.