Hydrolytic precipitation of calcium polyvanadates from vanadium(IV) and vanadium(V) solutions

The effect of VO²⁺ ions on the composition and kinetics of calcium polyvanadate precipitation from solutions with 1.5 ≤ pH ≤ 9 at 80–90°C has been studied. For 1,5 ≤ pH < 3 and V⁴⁺/V⁵⁺ = 0.11–9, the precipitated compounds have the general formula Ca _x V _y ⁴⁺ V _12?y ⁵⁺ O_31?δ · nH₂O (0.8 ≤ x ≤ 1.06, 2 ≤ y ≤ 3, 0.94 ≤ δ ≤ 1.5). The maximum vanadium(IV) proportion (y = 3) in the precipitates is achieved when V⁴⁺/V⁵⁺ = 0.5?1.0 in the solution and pH is 3. Polyvanadate precipitation at pH 1.7 has a long induction period (up to 30 min), which is not observed for V⁴⁺/V⁵⁺ > 0.1. Precipitation in solutions with pH 3 occurs only when VO²⁺ ions are added, with a maximum rate near V⁴⁺/V⁵⁺ = 0.2 and in presence of chloride ions. The processes are controlled by a secondorder reaction on the polyvanadate surface.     

Hydrothermal Synthesis and Characterization of (H3N(CH2)4NH3)[V6O14]

A new layered vanadium oxide [H₃N(CH₂)₄NH₃](V₆O₁₄) was synthesized hydrothermally under autogenous pressure at 180°C for 48 h from a mixture of H₂N(CH₂)₄NH₂ and V₂O₅ in aqueous solution. Its structure was determined from single-crystal X-ray diffraction at room temperature with final R=0.0774 and R_w=0.0893. It crystallizes in the monoclinic system (space group P2₁/n with a=9.74(2) Å, b=6.776(5) Å, c=12.60(2) Å, β=96.1(1)°, V=827(2) ų and Z=2). This compound contains mixed-valence V⁵⁺/V⁴⁺ vanadium oxide layers built from [V^VO₄] tetrahedra and pairs of edge-sharing [V^IVO₅] square pyramids with protonated organic amines occupying the interlayer space.     

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.     

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.     

Etude structurale d'un pyrochlore non stoechiométrique et désordonné contenant Bi(III) et Bi(V)

The formula of the compound [K_1.14Bi^III_0.37] [Bi^III_0.27Bi^V_1.73] [O_4.9OH_1.1]OH_0.8 has been established by means of analytical methods and least-squares refinement of the structure based upon X-ray powder diffraction data. This nonstoichiometric pyrochlore-type compound (a = 10.965(1) Å) is highly disordered: A fraction of the 16d positions of S.G. Fd3m is occupied by K⁺ and Bi³⁺ ions and a fraction of the 48 f positions by O^2? and OH^? ions; furthermore, octahedral sites are shown to accommodate both Bi³⁺ and Bi⁵⁺ ions. It is suggested that the use of 32e (rather than 8b) positions for anions can account for an upper limit of the 16d positions occupancy factor.     

Composition and formation kinetics of sodium polyvanadates in vanadium(IV, V) solutions

We study how VO²⁺ ions affect the composition and formation kinetics of polyvanadate precipitates in solutions with 1 ≤ pH ≤ 3 at 80–90°C. The compounds have the general formula Na_2.1?x H_xV _y ⁴⁺ V _12?y ⁵⁺ O_31?δ. nH₂O (0 ≤ x ≤ 1.1, 0.2 ≤ y ≤ 2.3, 0.1 ≤ δ ≤ 1.4). The maximal vanadium(IV) concentration in the precipitates y = 2.2 and 2.3) is achieved for the V⁴⁺/V⁵⁺ ratio in the solution equal to 0.5 and 0.3 and pH of 1.7 and 3.0, respectively. The polyvanadate precipitation at pH 1.7 has a long induction period, which is not observed when V⁴⁺/V⁵⁺ > 0.02. In the solutions with pH 3.0, the precipitation occurs only when VO²⁺ are added. The processes are controlled by second-order reactions on the polyvanadate surface.     

Synthesis and crystal structure of mixed metal(III) tungstenyl(VI) ortho-pyrophosphates

The series of isotypic anhydrous ortho-pyrophosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, V, Cr, Fe, Mo, Ru, Rh, In, Ir) was obtained via vapor phase moderated solid state reactions in sealed ampoules. The crystal structure of the phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: V, Ru, Rh) was solved from single crystal X-ray data (C2/c, Z = 16). Fairly regular MO₆ and distorted WO₆ octahedra share vertices with PO₄ and P₂O₇ units to form a 3D network. For the ortho-pyrophosphates with M: V³⁺, Cr³⁺, and Fe³⁺ the oxidation state of M is confirmed by magnetic measurements. ³¹P-MAS-NMR spectra of the diamagnetic phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, In, Ir) show surprisingly different isotropic chemical shifts for the seven phosphorus sites. V^III(W^VIO₂)₂(P₂O₇)(PO₄) occurs as equilibrium phase in the quasi-binary system (V_1–xW_x)OPO₄ at x = 0.67 and exhibits a small homogeneity range 0.60 ≤ x ≤ 0.67. The scandium compound shows a fully inverted occupancy of the M sites according to the formulation W(Sc_1/2W_1/2O₂)₂(P₂O₇)(PO₄).     

The crystal structure of eulytite Na3Bi5(PO4)6

The crystal structure of Na₃Bi₅(PO₄)₆ was solved using the single-crystal X-ray diffraction technique. The structural refinement has led to a reliability factor of R₁=0.0257 (wR₂=0.0533) for 428 independent reflections. This compound was found to crystallize in the cubic system (space group I4̄3d) with eulytite structure and the lattice parameters: a=10.097 (4) Å, V=1029.38 ų, Z=2, D_calc.=5.43 g cm⁻³ (D_exp.=5.32(5) g cm⁻³). The structure is characterized by the existence of one single general position (48a) for oxygen anions and two distinguished positions (16c) occupied by Na⁺ and Bi³⁺ cations, respectively. The site occupation factors are equal to 3/8 and 5/8 for sodium and bismuth, respectively. Although all PO distances are identical (1.529(4) Å), the OPO angles ranging from 108.06 (15) to 112.32 (31)°, show that [PO₄]³⁻ are rather distorted. Both sodium and bismuth cations are located in octahedral sites with corresponding mean distances of NaO and BiO equal to 2.428 and 2.386 Å, respectively. As expected from the close values of the ionic radii of Na⁺ and Bi³⁺, these distances lie in the same range.     

Exploration of Metal-Metal Charge Transfer (MMCT) and its Effect in Generating New Colored Compounds in Mixed Metal Oxides

Compounds belonging to the palmierite structure, (Zn_3−xM_x)A₂O₈ (M=Co, Ni, Cu and A=V, P) have been prepared employing solid state methods. The transition metal substituted compounds of Zn₃V₂O₈ exhibits colors that are unique varying from mint green to forest green for Co²⁺ ions. The observed colors were understood based on the allowed d-d transitions and metal to metal charge transfer (MMCT) transitions. The MMCT transitions involve partially filled d-orbitals of Co²⁺ (3d⁷), Ni²⁺ (3d⁸), and Cu²⁺ (3d⁹) ions and the V⁵⁺ ions (3d⁰). The spinel compounds, Zn_2−xCo_xMO₄ (M=Ti, Sn) were also prepared to understand the MMCT transitions in the compounds. Band structure calculations were carried out to understand the participating orbitals near the Fermi level and the band gap. The calculations support the idea that the substitution of transition elements in the palmierite structure reduces the overall band gap from 3.18 eV for Zn₃V₂O₈ to 2.61 eV Zn_2.5Co_0.5V₂O₈ compound. This indicates the substitution of transition elements provide a tool towards band gap engineering.     

Crystal structure, thermal and magnetic properties of Cr2V4O13

Cr₂V₄O₁₃, a tetravanadate of Cr³⁺ has been prepared by repeated heating of stoichiometric amounts of Cr₂O₃ and V₂O₅ and its crystal structure is refined by Rietveld refinement of the powder XRD data. This compound crystallizes in a monoclinic lattice with unit cell parameters: a=8.2651(3), b=9.2997(3), c=14.5215(5) Å, β=102.618(3)°, V=1089.21(6) Å³ and Z=4 (Space group: P2₁/c). The U shaped (V₄O₁₃)⁶⁻ formed by corner connected VO₄ tetrahedra links the Cr₂O₁₀ (dimers of two edge shared CrO₆ octahedra) forming a three dimensional network structure of Cr₂V₄O₁₃. This compound is stable up to 635 °C and peritectically decomposes to orthorhombic CrVO₄ and V₂O₅ above this temperature. A possible long range antiferromagnetic ordering below 10 K is suggested from the squid magnetometry and electron paramagnetic resonance (epr) spectroscopic studies of Cr₂V₄O₁₃.     

Synthesis, Crystal Structure and Thermal Analysis of (TAGH)2(TNR)

A new energetic compound (TAGH)₂(TNR) (TAG: triaminoguanidine, TNR: 2,4,6-trinitroresorcinol) was prepared by reacting triaminoguanidine with 2,4,6-trinitroresorcinol (styphnic acid) in aqueous solution under nitrogen atmosphere, and characterized by elemental analysis and Fourier transform infrared (FTIR) spectra. Its crystal structure was determined by single crystal X-ray diffraction analysis. The crystal belonged to a monoclinic, C 2/c space group. The unit cell parameters were as follows: a=2.2892(6) nm, b=1.2802(3) nm, c=1.3661(4) nm, β=111.174(5)°, V=3.7333(16) nm³, and Z=8. The compound consisted of two cations C(N₂H₃)₃⁺ and an anion (C₆HN₃O₈)²⁻. The C(N₂H₃)₃⁺ and (C₆HN₃O₈)²⁻ were bonded together by electrostatic attraction and hydrogen bonds, and this effect made the compound more stable. The thermal analysis of the compound was studied by using differential scanning calorimetry (DSC), thermogravimetry-derivative thermogravimetry (TG-DTG). Under nitrogen atmosphere with a heating rate of 10 K·min⁻¹, the thermal decomposition of the compound contained only one intense exothermic decomposition process in the range of 450.1-477.7 K in the DSC curve, and the decomposition products were nearly gaseous products.     

Electronic State of Vanadium Ions in Li1+xV3O8 According to EPR Spectroscopy

EPR spectroscopy is used to study the electronic state of vanadium ions in HT- and LT-Li_1+xV₃O₈. It is shown that in both cases the EPR spectra observed are attributed to vanadyl VO²⁺ ions (localized electron centers) with weak exchange interaction. The other type of registered electrons is characterized by larger mobility through a few V⁵⁺ ions, i.e., by a higher degree of delocalization (electron gas). Based on the analysis of the temperature dependence of the EPR line width, it is stated that the exchange interaction between localized electron centers proceeds through electron gas (C-S-C relaxation). It is found that HT-Li_1+xV₃O₈ differs from LT-Li_1+xV₃O₈ by the sloping form of its spectrum at g_∥ range connected with two types of VO²⁺ ions different in the direction of the crystal field axis corresponding to a short V=O²⁺ bond.     

2D-layered structure of coordination polymer,zinc trifluoroacetate-1,3-bis(4-pyridyl)propane

Compound [Zn(CF₃CO₂)₂(Bpp)₂], where Bpp is 1,3-bis(4-pyridyl)propane, was synthesized and its structure and luminescent properties were determined. Crystals are monoclinic, space group C2/c, a = 21.261(1) Å, b = 17.642(1) Å, c = 18.632(1) Å, β = 115.85(1)°, V = 6289.3(6) ų, ρ_calcd = 1.453 g/cm³, Z = 8. The structure comprises 2D neutral layers of conjugated multiunit rings composed of four Zn²⁺ ions united by four bridging Bpp ligands. Each of two crystallographically nonequivalent Zn atoms is coordinated at the octahedra apices to four nitrogen atoms of two Bpp ligands and two O(CF₃CO₂) atoms. Trifluoroacetate anions are coordinated to Zn²⁺ ions in monodentate manner. The compound exhibits photoluminescence in solid state.     

A novel three-dimensional cobalt(II)-radical complex Co(NITmPy)2[N(CN)2]2: Structure and magnetic properties

A novel three-dimensional cobalt(II)-radical complex {Co(NITmPy)₂[N(CN)₂]₂}_n (NITmPy = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) is prepared and characterized by X-ray crystallography. The complex crystallizes in the monoclinic system, space group P2₁/c, with unit cell parameters a = 12.5775(5) Å, b = 10.9340(5) Å, c = 11.6134(5) Å, β = 108.1320(10)°; V = 1517.79(11) ų, ρ_calcd = 1.443 g/cm³, and Z = 2 for R ₁ = 0.0463. In the complex, each cobalt ion is six-coordinate with four nitrogen atoms from four N(CN) ₂ ^t- ligands and two nitrogen atoms of pyridyl groups, and the [Co(NITmPy)₂]²⁺ units are linked by N(CN) ₂ ^t- μ-bridging ligands to form a three-dimensional structure. The variable-temperature magnetic susceptibility data show that the complex exhibits weak antiferromagnetic interactions.     

Topotactic insertion of lithium in the layered structure Li4VO(PO4)2: The tunnel structure Li5VO(PO4)2

A new V(III) lithium phosphate Li₅VO(PO₄)₂ has been synthesized by electrochemical insertion of lithium into Li₄VO(PO₄)₂. This phase, which crystallizes in the space group I4/mcm, exhibits a tunnel structure closely related to the layered structure of Li₄VO(PO₄)₂ and to the tunnel structure of VO(H₂PO₄)₂. The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H₂PO₄)₂ and going to the final phase Li₅VO(PO₄)₂ are explained on the basis of the flexible coordinations of V⁴⁺ and V³⁺ species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality.     

A new cyanobridged one-dimensional coordination polymer based on the octahedral rhenium cluster [Re6Se8(CN)6]4−: Synthesis and crystal structure of [{Cu(H2O)0.5(en)2} {Cu(en)2}Re6Se8(CN)6]·3H2O

The rhenium cluster complex [{Cu(H₂O)_0.5(en)₂} {Cu(en)₂} Re₆Se₈(CN)₆]·3H₂O has been obtained by the reaction of an aqueous solution of K₄[Re₆Se₈(CN)₆]·3.5H₂O with an aqueous solution of Cu(en)₂Cl₂ using cross diffusion through a gel. The structure of the compound has been characterized by a single-crystal X-ray diffraction method (a = 10.690(3) Å, b = 15.035(5) Å, c = 25.847(8) Å, V = 4154(2) ų, Z = 4, space group P2₁2₁2₁, R = 0.0651). Cluster anions [Re₆Se₈(CN)₆]^4? in the complex are connected with Cu²⁺ cations by cyano bridges resulting in zigzag chains. Coordination environment of cations is completed by ethylenediamine molecules. Additionally each cluster anion is coordinated by one terminal fragment {Cu(H₂O)_0.5(en)₂}.     

Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Crystal Structure of a New Ammonium Potassium Selenomolybdate Compound K3.31(NH4)0.69[Se2Mo5O21]·2H2O

An inorganic compound formulated as K_3.31(NH₄)_0.69[Se₂Mo₅O₂₁]·2H₂O has been synthesized by conventional solution method and characterized by scanning electron microscopy, IR, UV-Vis spectroscopies behaviors. The structure of the title compound has been determined from a single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P2₁/n, with a?=?9.9371(2) ?, b?=?23.3545(2) ?, c?=?10.5179(2) ?, β?=?114.12(3)°, V?=?2227.7(5) ?³ and Z?=?4. It was revealed that the Strandberg-type polyoxoselenomolybdate cluster can be considered as a ring formed by five distorted edge- and corner-sharing MoO₆ octahedra, capped on both poles by a selenate pyramids sharing three vertices with the ring molybdenum centers. The Strandberg clusters are connected with ammonium ions and water molecules through hydrogen-bonding interactions which ensure the cohesion of the structure into a three-dimensional network.     

Hydrothermal synthesis and crystal structure of a layered vanadium oxide with an interlayer metal coordination complex: [Co(phen)3][V10O26]·H2O

A novel compound, [Co(phen)₃][V₁₀O₂₆]·H₂O, was hydrothermally synthesized and characterized by single-crystal X-ray diffraction. This compound crystallizes in the orthorhombic space group Ccca with a=13.447(3), b=29.936(6), c=23.252(5) Å, V=9360(3) Å³, Z=8 and R=0.0285. Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 1.36<θ<24.99°. The structure of the compound consists of vanadium oxide layers, which are built up from the infinite VO₄ chains by corners and edges sharing. The [Co(phen)₃]²⁺ complexes occupy the interlayer space and contact each other via π−π stacking interactions of the phen groups to form infinite one-dimensional chains.     

Intense turquoise colors of apatite-type compounds with Mn5+ in tetrahedral coordination

The solid solutions of chlorapatite compounds Ba₅Mn_3−xV_xO₁₂Cl (x = 0–3.0) and Ba₅Mn_3−xP_xO₁₂Cl (x = 0–3.0) have been synthesized through solid state reactions and Pechini or sol–gel method using citric acid. The colors of the samples change from white (x = 3.0) through turquoise (x = 1.5) to dark green (x = 0) with increasing amount of manganese. Optical measurements reveal that the origin of the color is presumably a combination of d–d transitions of Mn⁵⁺ and cation-anion charge transfer from transition metals to oxygens. Near IR reflectance measurements indicate that synthesized compounds are promising materials for “cool pigments” applications. Magnetic measurements verify that manganese has two unpaired electrons and exhibits 5 + oxidation state. The IR spectra change systematically with sample compositions and the fingerprint region (700 cm⁻¹ to 1100 cm⁻¹) indicates characteristic bands belonging to (MnO₄)³⁻, (VO₄)³⁻ and (PO₄)³⁻ functional groups. Structure refinements using neutron data confirm that Mn⁵⁺, V⁵⁺ and P⁵⁺ cations occupy the tetrahedral sites in the apatite structure.