Voltammetric study of the reduction process of ethylenediaminetetraacetatovanadium(IV): oxidation-state-dependent speciation

Cyclic voltammetry, differential-pulse polarography (d.p.p.), and direct-current tast polarography (d.c.t.p.) were used to study the electrochemical reduction of ethylenediaminetetraacetatovanadium(IV) [V(IV)OEDTA^2?]. The two-electron reduction wave of V(IV)OEDTA^2? is gradually split into two one-electron waves when the concentration of the supporting electrolyte is increased. A detailed study of the electrochemistry of V(III)EDTA^? allowed the conclusion that the two one-electron waves of V(IV)OEDTA^2? reflect the reduction sequence V(IV)OEDTA^2?$\text{+e}{}^{\mathrm{?}}$ V(III)EDTA^?$\text{+e}{}^{\mathrm{?}}$|$\text{?e}{}^{\mathrm{?}}$ V(II)EDTA^2?. The process responsible for the observed “chemical” peak separation was found to be ion pairing, by which the reduction of V(IV)OEDTA^2? is facilitated. A method is presented by which the parallel determination of V(IV) and V(III) (when present as the appropriate EDTA complexes) is possible with d.p.p, or d.c.t.p.     

Monitoring of V(IV) and V(V) in Etnean drinking-water distribution systems by solid phase extraction and electrothermal atomic absorption spectrometry

Monitoring activities carried out since 1994 showed the presence of significant levels of vanadium in drinking waters delivered in a lot of Etnean towns. The highest vanadium concentration was found in ground waters collected in the drainage gallery Ciapparazzo located on the Northwestern flank of Mt. Etna in Bronte's area (Catania, Italy). This drainage gallery, with a flow rate of near 500 l s^− 1, is an important water source for several towns of the Etnean province. On account of different toxicological behaviours of V(IV) and V(V), which are the only possible oxidation states in aqueous media, a research project was set up to evaluate the ratio between their concentrations before and after disinfection treatments (chlorination or UV irradiation). Data were acquired in the most representative sites of the drainage gallery and the distribution network to evaluate the effect of residence times and disinfection treatments on possible species interconversion. The average total concentration of vanadium was 165 μg l^− 1. Speciation analyses performed by solid phase extraction of both species followed by furnace atomic absorption spectrometric determination of V(IV) eluates revealed that the latter was the predominant species (90-100%) in untreated waters. Moreover, among the two disinfecting treatments applied by the water supplier, only sodium hypochlorite altered the species ratio and determined an instant increase of near 20% in V(V) relative concentration. No significant effect was observed as residence time varied in the drainage gallery or in the distribution systems. Other physico-chemical and chemical parameters (i.e. pH, E_H, water temperature, electrical conductance, dissolved oxygen as well as major and minor inorganic cations and anions) were determined in the collected water samples to evaluate if they are proper or not for interconversion of the two V species. Redox potential of the water was also correlated to the percentage of V(IV).     

Cationic Homoleptic Vanadium(II), (IV), and (V) Complexes Arising from Protonolysis of [V(NEt2)4]

At least three different cationic species arise in the classic protonolysis of [V^IV(NEt₂)₄] with a borate ammonium salt. The unexpected formation of the vanadium(V ) species [V(NEt₂)₄][B(C₆H₅)₄] (shown in the picture without its counterion) underlines the problem of deducing the true oxidation state of vanadium species in Ziegler–Natta reactions.     

Synthese und Struktur von Vanadium(III)- und Vanadium(IV)-silanolaten

Synthesis and Structures of Vanadium(III) and Vanadium(IV) Silanolates The syntheses of the new and partially known vanadium(III)-silanolate complexes [{V(OSiMe^t₂Bu)₃}₂(THF)] ( 1 ), [Li(THF)₂V(OSiMe^t₂Bu)₄] ( 2 ), [V(OSiMe^t₂Bu)(lut)] ( 3 ), V(OSiPh₃)₃(THF)₃ ( 4 ), [Li(THF)₄][V(OSiPh₃)₄](THF)₂ ( 5 ), [Li(DME)VMes(OSiMe^t₂Bu)₃] ( 7 ), [Li(THF)₄][VMes · (OSiPh₃)₃] ( 8 ), [Li(THF)₄][VMes₃(OSiMe^t₂Bu)] ( 9 ), and Na[VMes₃(OSiPh₃)](THF)₄ ( 10 ) as well as the vanadium(IV) compounds [V(OSiPh₃)₄] ( 6 ), [VMes₃(OSiMe^t₂Bu)] ( 11 ) and [VMes₃(OSiPh₃)] ( 12 ) are reported. In most cases the vanadium atom displays a coordination number of four. The dimeric structure of 1 with coordination numbers of four and five, respectively, has been deduced from molecular mass measurements, mass spectrometry and its magnetic properties. The crystal structures of compounds 2 , 4 , 5 , 9 and 11 were resolved. Complex 2 resembles a bridged contact ion pair in which both metal centres are in a tetrahedral coordination environment. In 4 the ligands are arranged trigonal bipyramidally with the THF molecules in the axial positions. Complexes 5 and 9 crystallize in separated ion paires with the vanadium in a tetrahedral coordination sphere. The crystal structure of 11 is analogous to that of 9 but with consequences due to the higher oxidation state. Oxidation of the vanadates(III), e. g. 5 , 9 and 10 , yields the corresponding vanadium(IV) compounds 6 , 11 and 12 .     

全钒液流电池高浓度下V(IV)/V(V)的电极过程研究

采用循环伏安、低速线性扫描和阻抗技术, 以石墨为电极, 研究了V(IV)/V(V)在较高浓度下的电极过程. 结果表明, 采用2.0 mol•L-1 的V(IV)溶液时, H2SO4浓度低于2 mol•L-1, V(IV)/V(V)反应极化大, 可逆性差, 表现为电化学和扩散混合控制; H2SO4浓度增至2 mol•L-1以上, V(IV)/V(V)反应的可逆性提高, 转为扩散控制, 且增加H2SO4浓度有利于阻抗的降低; 但H2SO4浓度超过3 mol•L-1, 溶液的粘度和传质阻力大, 阻抗反而增大. 在3 mol•L-1的H2SO4中, 随着V(IV)浓度的增加, 体系的可逆性和动力学改善, 阻抗减小; 但V(IV)浓度超过2.0 mol•L-1, 较高的溶液粘度导致溶液的传质阻力迅速增加, V(IV)/ V(V)的电化学性能衰减, 阻抗增大. 因此, 综合考虑电极反应动力学和电池的能量密度两因素, V(IV)溶液的最佳浓度为1.5～2.0 mol•L-1, H2SO4浓度为3 mol•L-1.     

Neue Heteropolyanionen des Wolframs mit Vanadium(IV) als Heteroatom

New Heteropolyanions of Tungsten with Vanadium(IV) as a Heteroatom The syntheses of two new heteropolyanions with vanadium as heteroatom are presented. They are characterized by X‐ray structure analysis and vibrational spectra. ((CH₃)₄N)₆Na₄[(VO(H₂O)₂)₂(WO₂)₂(BiW₉O₃₃)₂]·18H₂O (1) crystallises in the triclinic crystal system (P1¯) with a = 13.299(3)Å, b = 13.554(3)Å, c = 18.620(4)Å and α = 90.22(3)°, β = 91.99(3)°, γ = 119.16(3)°. Na_5.4K_6.6[(VO)₃(AsW₉O₃₃)₂]·29H₂O ( 2 ) crystallises in the hexagonal space group P6₃/mmc with a = 15.124(3)Å and c = 24.209(5)Å. The polyanion in 1 is isostructural to anions of the M₂X₂W₂₀‐typ with other heteroatoms. They are built up by two β‐B‐[SbW₉O₃₃] fragments, which are derived from defect structures of the Keggin anion. These subunits are connected by two formal WO₂ groups with further stabilisation by addition of two M(H₂O)₃ groups leading to the M₂X₂W₂₀‐type heteropolytungstates. The anion in 2 is a new example of the M₃X₂W₁₈‐type, which contains two α‐B‐[XW₉O₃₃]‐units connected via a belt of three transition metal atoms.     

Oxovanadium(IV) and (V) complexes of acetylpyridine-derived semicarbazones exhibit insulin-like activity

Reaction of 2-acetylpyridine semicarbazone (H2APS), 3-acetylpyridine semicarbazone (H3APS) and 4-acetylpyridine semicarbazone (H4APS) with [VO(acac)₂] (acac = acetylacetonate) gave [VO(H2APS)(acac)₂] (1), [VO(H3APS)(acac)₂] (2) and [VO(4APS)(acac)(H₂O)] · 1/2H₂O (3). Oxidation of complex 1 in acetonitrile gave [VO₂(2APS)] (4). The crystal structures of complexes 1 and 4 have been determined. Complexes 1–3 were able to enhance glucose uptake and to inhibit glycerol release from adipocytes, which indicate their potential to act as insulin-mimics.     

Inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology

The paper presents a procedure for the multi-element inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology. Total As(III, V), Se(IV, VI) and Sb(III, V) were determined according to the following procedure: titanium dioxide (TiO₂) was used to adsorb inorganic species of As, Se and Sb in sample solution; after filtration, the solid phase was prepared to be slurry for determination. For As(III), Se(IV) and Sb(III), their inorganic species were coprecipitated with Pb-PDC, dissolved in dilute nitric acid, and then determined. The concentrations of As(V), Se(VI) and Sb(V) can be calculated by the difference of the concentrations obtained by the above determinations. For the determination of As(III), Se(IV) and Sb(III), palladium was chosen as a modifier and pyrolysis temperature was 800 °C. Optimum conditions for the coprecipitation were listed for 100 ml of sample solution: pH 3.0, 15 min of stirring time, 40.0 μg l⁻¹ Pb(NO₃)₂ and 150.0 μg l⁻¹ APDC. The proposed method was applied to the determination of trace amounts of As(III, V), Se(IV, VI) and Sb(III, V) in river water and seawater.     

Crystal Structure and Magnetic Properties of a Vanadium (IV) Pyrophosphate: Rb2V3P4O17

The crystal structure of Rb₂V₃P₄O₁₇ has been determined from single-crystal X-ray diffraction data. Rb₂V₃P₄O₁₇ crystallizes in the orthorhombic space group Pnma (No. 62) with a = 17.502(7), b = 7.292(2), c = 11.399(6) ų, V = 1455(1) ų, Z=4, R=0.0295, R_W = 0.0320 for 1129 unique reflections with I > 2.5 σ(I). The structure contains intersecting tunnels where the Rb⁺ cations are located. The framework can be described as consisting of V²O₁₀ units formed from one VO₅ square pyramid and one VO₆ octahedron sharing a corner, and infinite chains of corner-shared VO₆ octahedra, which are linked in three dimensions by pyrophosphate groups. The structural formula is Rb₂(VO)₃(P₂O₇)₂. A single-phase product can be obtained by heating appropriate amounts of Rb₄V₂O₇, VO₂, V, and P₂O₅ in an evacuated fused silica tube at 950°C. Powder magnetic susceptibility data confirm the presence of V⁴⁺ (d¹) ions without magnetic ordering down to 3 K.     

Extraction of Vanadium (IV) with DI-2-Ethylhexylphosphoric Acid

Abstract

It was established with the use of electron and ESR spectroscopic methods that in the presence of sodium sulfate, the extraction of vanadium (IV) with di-2-ethylhexylphosphoric acid takes place by a cation-exchange mechanism giving rise to two complex compounds of vanadium (IV) oxocation with sulfuric and di-2-ethylhexylphosphoric acid anions. The vanadium (IV) oxocation sulfate complex extracted in the solid state was examined with X-ray structural analysis. It was shown that the vanadium (IV) oxocation sulfate complex trihydrate crystallizes in the centrosymmetrical space group to form dimers with bridging sulfate groups.     

钒的羰基化合物V(CO)_n的电子结构研究

用限制性的CNDO/2法研究具有开壳层结构V(CO)_x(n=1～6)的各种构型和轨道.给出轨道能级相关图,阐明了各种构型的关系及稳定性.     

Catalytic Adsorptive Stripping Voltammetry of Germanium(IV) in the Presence of Gallic Acid and Vanadium(IV)‐EDTA

A highly sensitive and selective catalytic adsorptive cathodic striping procedure for the determination of trace germanium is presented. The method is based on adsorptive accumulation of the Ge(IV)‐gallic acid (GA) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is enhanced catalytically by addition of vanadium(IV)‐EDTA. The optimal experimental conditions include the use of 0.03 mol/L HClO₄ (pH1.6), 6.0×10^?3 mol/L GA, 3.0×10^?3 mol/L V(IV), 4.0×10^?3 mol/L EDTA, an accumulation potential of ?0.10 V(vs. Ag/AgCl), an accumulation time of 120 s and a differential pulse potential scan mode. The peak current is proportional to the concentration of Ge(IV) over the range of 3.0×10^?11 to 1.0×10^?8 mol/L and the detection limit is 2×10^?11 mol/L for a 120 s adsorption time. The relative standard deviation at 5.0×10^?10 mol/L level is 3.1%. No serious interferences were found. The method was applied to the determination of germanium in ore, mineral water and vegetable samples with satisfactory results.     

Vanadium (V, IV) und Uran (VI)

Ohne Zusammenfassung     

双极谱峰指示催化动力学极语法测定痕量钒

在硫酸介质中,以酒石酸为活化剂,痕量机对溴酸钾氧化乙基极的反应具有极强的催化作用,研究了最佳反应条件,且发现在氨性缓冲溶液中乙基橙及其氧化产物具有良好的极谱峰,以极谱法监测催化反应过程中乙基橙及其氧化产物浓度的变化,建立了催化动力学极谱法测定痕量帆的新方法。方法的线性范围为０．２５～３．５μｇ／Ｌ,检出限为０．１２μｇ／Ｌ。应用于食品中痕量钒的测定,结果满意。     

Vanadium(IV) und Molybd?n (V)

Ohne Zusammenfassung     

Synthesis and Structural Characterization of a Novel Heterodinuclear Vanadium(IV)‐Nickel(II) Complex

A novel V^IV‐Ni^II heterodinuclear complex [VO(cat)₂][Ni(1, 2‐PDA)₂H₂O] ( 1 ) (cat = catechol; 1, 2‐PDA = 1, 2‐propane diamine) was synthesized at low temperature (10 °C) and characterized by IR spectroscopy and X‐ray diffraction. A novel Ni–O=V structure exists in the complex, the vanadyl–catechol moiety and the nickel–diamine moiety are connected by an oxygen bridge; all molecules are further assembled into crystallites by O–H ··· O hydrogen bonds.     

钒(Ⅴ)-硫氰酸盐-碱性三芳基甲烷染料的显色反应研究

研究了在表面活性剂存在下,钒(V)与硫氰酸盐和结晶紫、孔雀绿、灿烂绿、甲基紫及维多利亚蓝4R等碱性三芳基甲烷染料形成离子缔合物的显色反应.讨论了钒(V)-硫氰酸盐-结晶紫-阿拉伯树胶体系的反应条件和分析特性。摩尔吸光系数为2.55×10⁵L·mol^-1·cm^-1.此法可用于铝合金中微量钒的测定。