Micellar Catalysis on the Redox Reaction of Ascorbic Acid-Vanadium(V) System

Stoichiometry of the redox reaction of vanadium(V) by ascorbic acid (H₂A) has been experimentally determined to be H₂A + 2V(V) → A + 2V(IV) + 2H ⁺ . Evidence of induced polymerization of acrylonitrile and the reduction of mercuric chloride indicates that a free-radical mechanism operates during the course of reaction. Vanadium(V) is only reduced to vanadium(IV). The kinetics of this redox reaction have been investigated spectrophotometrically at 35°C in acidic media of H₂SO₄. In this kinetic study we have observed the nature of vanadium(V)-H₂A interaction in presence of anionic surfactant of SDS. In V(V)-H₂A system, the addition of anionic surfactant (SDS) enhanced the reaction rate and shows catalytic effect. This trend was explained by the incorporation/solubilization of vanadium(V) and ascorbic acid in the Stern layer.     

Oxovanadium(IV,V) Complexes with 2‐Acetylpyridine‐2‐furanoylhydrazone (Hapf) as Ligand. X‐Ray Crystal Structures of [VO2(apf)] and [V2O2(μ‐O)2(apf)2]

The preparation of oxovanadium(IV, V) coordination compounds with 2‐acetylpyridine‐2‐furanoylhydrazone (Hapf) is described. [VO(apf)(acac)] was prepared from oxovanadium(IV) diacetylacetonate [VO(acac)₂] by reaction with Hapf in methanol or dichloromethane. The complex is paramagnetic and its EPR spectrum is consistent with an octahedral coordination for the vanadium(IV) atom. Voltammetry studies of [VO(apf)(acac)] indicate an irreversible oxidation, in agreement with the chemical behavior of the compound in solution. The vanadium(IV) complex undergoes slow oxidation in alcoholic solution, losing the acetylacetonate ligand to form [VO₂(apf)] and [V₂O₂(μ‐O)₂(apf)₂]. The crystal structures of these last compounds were determined by X‐ray diffraction methods. [V₂O₂(μ‐O)₂(apf)₂] crystallizes monoclinic [P2₁/c, Z = 2, a = 817.400(10), b = 1650.90(3), c = 984.70(2) pm, β = 112.7190(10)°]. The crystal structure consists of dimeric units, in which two μ‐oxo ligands subtend asymmetric bridges between the vanadium atoms in a very distorted octahedral coordination. In the crystal of [VO₂(apf)], orthorhombic [Pnma, Z = 4, a = 1630.000(10), b = 675.10(4), c = 1136.40(2) pm], the vanadium(V) atom is pentacoordinated.     

Spectrophotometric Studies on the equilibria of vanadium(V)-4-(2-Pyridylazo)-resorcinol-polyaminopolycarboxylate systems

The complexation equilibria in the VO⁺₂-PAR-polyaminopolycarboxylate-(EDTA and CDTA) systems were studied spectrophotometrically in order to establish the action of CDTA in the spectrophotometric determination of vanadium(V) with PAR. Analysis of absorbance-pH curve and ligand exchange equilibria yielded the following values of the constants; K_VO2HR=lO^17.16, K^H_VO2HR=10^-3.95, K_VO2R=10^18.81, K_VO2EDTA=10^17.38 and K_VO2CDTA=10^16.59 at 20°C and ionic strength 0.1 (KCl). Based on these constants, the selective masking behavior of CDTA for the VO⁺₂-PAR system can be quantitatively explained.     

Molecular Mechanics Calculations on Chelates of Titanium(IV), Vanadium(IV/V), Copper(II), Nickel(II), Molybdenum(IV/V), Rhenium(IV/V) and Tin(IV) with Di- and Tridentate Ligands Using the New Extensible Systematic Force Field (ESFF)—An Empirical Study

Force field calculations were performed on a series of 27 transition metal complexes of titanium(IV), vanadium(IV/V), copper(II), nickel(II), molybdenum(IV/V), rhenium(IV/V), and tin(IV) with a broad variety of di- or tridentate ligands in order to find a reliable scheme for determining the molecular structure of such chelates with the new Extensible Systematic Force Field (ESFF). A good agreement between theoretical results and experimental data was achieved. In some cases an unspecific fitting of the force field was necessary.     

Nanoparticle supported,magnetically separable vanadium complex as catalyst for selective oxidation of sulfides

A magnetically recyclable vanadium(V) catalyst was synthesized by covalent anchoring of VO(salen)Cl on silica-coated Fe₃O₄ nanoparticles. This straightforward preparation yields magnetically separable Fe₃O₄@SiO₂@VO(salen) nanoparticles with high vanadium loading. These nanoparticles were efficient catalysts for selective oxidation of sulfides to corresponding sulfoxides with urea hydrogen peroxide in excellent yields. Leaching and recycling experiments revealed that the nanocatalyst can be applied for nearly complete oxidation of sulfides for at least five successive cycles.     

Maleanilic Acids as Highly Selective Reagents for the Amperometric Determination of Thorium (IV)

Abstract

Thorium has been determined amperometrically at an applied e. m. f. of -1.2V with fifteen maleanilic acids. Out of these o-tolyl, p-tolyl, 1-naphthyl, 2-naphthyland 4-amino maleanilic acid were found promising analyticalreagentsand most effective. Th(IV) in the range 6.60 to 2350.0 mg per 100 ml can be determined with an error of ± 0.2%. The interference of fifty-five ions were studied and only five ions Zn(II), Pb(II), Fe(III), UO₂ (II) and Zr(IV) interfered. which could be masked by the addition of S₂O² ₃ or SCN^?, Cl^? or SO^2- ₄, SCN^? or citrate, citrate or tartrate and P₂O^4- ₇ respectively.     

Speciation of vanadium in soil

A method for speciation of vanadium in soil is presented in this work. The sequential extraction analysis procedure of Tessier et al. for heavy metals was used for the vanadium separation. The method consists of sequential leaching of the soil samples to separate five fractions of metals: (1) exchangeable, (2) bound to carbonates, (3) bound to Fe-Mn oxides, (4) bound to organic matter and (5) residual. The leaching solutions of Tessier were used for the vanadium extraction, only for the residual fraction the HClO₄ was replaced with H₂SO₄. The optimum conditions for leaching of vanadium from soil (weight of sample, concentration and volume of extractants, time of extraction) were chosen for each fraction. A sensitive, spectrophotometric method based on the ternary complex V(IV) with Chrome Azurol S and benzyldodecyldimethylammonium bromide (ε=7.1×10⁴ l mol⁻¹ cm⁻¹) was applied for the vanadium determination after separation of V(V) by solvent extraction using mesityl oxide and reduction of V(V) using ascorbic acid. This method was applied for vanadium speciation in soil from two different regions of Poland: Upper Silesia (industrial region) and Podlasie (agricultural region). The content of vanadium in the fractions of Upper Silesia soil was respectively (in 10⁻³%): I, 3.39; III, 4.53; IV, 10.70; V, 8.70 and it was the highest in the organic fraction, indicating input by anthropogenic activities. The content of vanadium in Podlasie soil was clearly lower and it was (in 10⁻³%): I, 2.07; III, 0.92; IV, 0.69; V, 1.23. The concentration of vanadium in fraction 2 of both soils was less than detection limit of applied method. The total content of vanadium in the five soil fractions was in good correlation with the total content of this element in both soils found after HF-H₂SO₄ digestion. Analysis using the ICP-AES method gave comparable results.     

Ein neuer Zugang zu Alkalivanadaten(IV,V) Die Kristallstruktur von Rb2V3O8

A New Access to Alkali Vanadates(IV,V) Crystal Structure of Rb₂V₃O₈ By heating vanadium(V) oxide with rubidium iodide to 500°C, the vanadium experiences partial reduction and Rb₂V₃O₈ is obtained. It has the fresnoite structure. Crystal data: a = 892.29(7), c = 554.49(9) pm at 20°C, tetragonal, space group P4bm, Z = 2. X-ray crystal structure determination with 620 observed reflexions, R = 0.027. V₂O₇ units share vertices with VO₅ square pyramids, forming layers; a layer can be regarded as association product of VO²⁺ and V₂O₇^4? ions. The Rb⁺ ions between the layers have pentagonal-antiprismatic coordination.     

Investigation on Concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） Redox Reaction by Rotating Disc Voltammetry

The kinetic characteristics of the concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） couple have been studied at a glassy carbon electrode in sulfuric acid using rotating-disc electrode and cyclic voltammetry. The kinetics of the Ⅴ（Ⅳ）/Ⅴ（Ⅴ） redox couple reaction was found to be electrochemically quasi-reversible with the slower kinetics for the Ⅴ（Ⅴ） reduction than that for the Ⅴ（Ⅳ） oxidation. And, dependence of diffusion coefficients and kinetic parameters of Ⅴ（Ⅳ） species on the Ⅴ（Ⅳ） and H2SO4 concentration was investigated. It is shown that the concentration of active species Ⅴ（Ⅳ） should be over 1 mol·L^-1 for the redox flow battery application. Further, with increasing the Ⅴ（Ⅳ） and H2SO4 concentration, the diffusion coefficients of Ⅴ（Ⅳ） were gradually reduced whereas its kinetics was improved considerably, especially in the case of Ⅴ（Ⅳ） and H2SO4 up to 2 and 4 mol·L^-1.     

Selective Sorption–Spectrometric Determination of Nanogram Amounts of Vanadium(IV) and Vanadium(V)

Conditions of the selective sorption–spectrometric determination of vanadium(IV) and vanadium(V) using sulfonitrophenol M were found. The determination of vanadium (visual test (RSD = 30%) using a reference color scale or quantitative determination (RSD < 10%) by diffuse reflectance spectra is performed immediately after the dynamic-mode sorption of its colored complexes with sulfonitrophenol M at pH 3.5 (vanadium(IV)) or with sulfonitrophenol M and hydroxylamine at pH 1.5 (vanadium(V), 650 nm) at the surface of polyamide membrane disks (d= 1 cm, l= 0.1 mm, m= 2.7 mg). The flow rate is 10–20 mL/min. The detection limit is 5–7 ng of vanadium in the support zone or 0.2–0.5 ng/mL. The determination of 0.5–5 ng/mL vanadium(V) at pH 1.5 does not interfere with 20-fold amounts of V(IV) and 1000-fold amounts of Ni, Zn, Cd, Mg, Co, Cr(III), Mn, PO^3- ₄, and F^–.     

Vanadium complexes with thiosemicarbazones: Synthesis,characterization, crystal structures and anti-Mycobacterium tuberculosis activity

The development of more efficient anti-tuberculosis drugs is of interest. Three oxovanadium(IV) and three cis-dioxovanadium(V) complexes with thiosemicarbazone derivatives bearing moieties with different lipophilicity have been prepared and had their inhibitory activity against Mycobacteriumtuberculosis H₃₇Rv ATCC 27294 evaluated. The analytical methods used by the complexes’ characterization included IR, EPR, ¹H, ¹³C and ⁵¹V NMR spectroscopies, elemental analysis, cyclic voltammetry, magnetic susceptibility measurement and single crystal X-ray diffractometry. [VO(acac)(aptsc)], [VO(acac)(apmtsc)] and [VO(acac)(apptsc)] (acac = acetylacetonate; Haptsc = 2-acetylpyridinethiosemicarbazone; Hapmtsc = 2-acetylpyridine-N(4)-methyl-thiosemicarbazone and Happtsc = 2-acetylpyridine-N(4)-phenyl-thiosemicarbazone) are paramagnetic and their EPR spectra are consistent with the monoanionic N,N,S-tridentate coordination of the thiosemicarbazone ligands, resulting in octahedral structures of rhombic symmetry and with the oxidation state +IV for the vanadium atom. As result of oxidation of the vanadium(IV) complexes above, the diamagnetic cis-dioxovanadium(V) complexes [VO₂(aptsc)], [VO₂(apmtsc)] and [VO₂(apptsc)] are formed. Their ¹H, ¹³C and ⁵¹V NMR spectra were acquired and support a distorted square pyramidal geometry for them, in accord with the solid state X-ray structures determined for [VO₂(aptsc)] and [VO₂(apmtsc)]. In general, the vanadium compounds show comparable or larger anti-M. tuberculosis activities than the free thiosemicarbazone ligands, with MIC values within 62.5–1.56 (μg/mL).     

Separation and determination of vanadium in fertiliser by capillary electrophoresis with a light-emitting diode detector

A method has been developed for determination of vanadium, as an anionic ternary complex of vanadium(V) with 4-(2-pyridylazo) resorcinol (PAR) and hydrogen peroxide, after separation by capillary electrophoresis (CE). The optimum conditions for the formation of the ternary complex were acetate buffer (3 mmol L(-1)) at pH 6 containing 0.15 mmol L(-1) PAR and 7.1 mmol L(-1) H(2)O(2). The CE separation was conducted using 15 mmol L(-1) acetate buffer at pH 6 as the background electrolyte; the separation potential was -30 kV and the injection time 100 s. The vanadium complex was detected photometrically at 568 nm, by use of a light-emitting diode (LED); the detection limit was 19 ppb. The method was applied to the analysis of vanadium in fertilisers. Clean-up of the digested fertiliser sample, with Sep-Pak C(18) coated with tetrabutylammonium hydroxide, before analysis was used to remove matrix ions which otherwise caused electrophoretic de-stacking. Vanadium levels found in the fertiliser samples by use of the CE method were found to be comparable with results obtained by HPLC and ICP-MS.     

Extraction-spectrophotometric study on the vanadium(V)-2,3-dihydroxynaphthalene — iodonitrotetrazolium chloride — water — chloroform system and its analytical application

The formation of a new ternary ion-associate complex of vanadium(V) with 2,3-dihydroxynaphthalene and iodonitrotetrazolium chloride with a composition ratio of 1:2:1 is reported. The complex is quantitatively extracted from water into chloroform. The molar absorptivity (ɛ) of the extract at λ _max=340 nm is 2.5 × 10⁴ dm³/mol cm, and Beer’s law is obeyed for concentrations ranging from 0.1 to 0.9 μg/cm³ V(V). The following constants are determined: the extraction constant, the association constant, the distribution constant, and the recovery factor. The effects of foreign ions and reagents are studied. A selective and sensitive method is developed for determination of vanadium in steels.     

Efficiency of electrochemical amination of anisole in aqueous-organic solutions of 4 M H2SO4

Cathodically initiated amination of anisole has been performed with the Ti(IV)-NH₂OH system in aqueous solutions of 4 M H₂SO₄ containing high concentration of acetic acid or acetonitrile. In electrolyses performed to reach full conversion of hydroxylamine, the isomeric anisidines obtained (2 para/ortho ∼ 3.9) with total yields referred to the current and amino radical source exceeded 80%.     

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.     

二个含水杨酰腙配体的钒配合物的合成与晶体结构研究

2种水杨酰腙配体H2L1(H2L1=邻羟基苯乙酮缩水杨酰腙)和H2L2(H2L2=水杨醛缩水杨酰腙)分别与VO(acac)2反应,合成了2个钒配合物[VOL1(C2H5O)]2(1)和[VOL2(i-C3H7O)](2),利用元素分析、红外光谱、紫外光谱和单晶衍射等手段进行表征。配合物1是由酚氧原子桥联2个金属中心形成的具有晶体学中心对称性的双核钒(V)配合物结构,每个V(V)原子具有扭曲的八面体配位构型。配合物2为单核结构,每个V(V)原子具有扭曲的四角锥配位构型,相邻的配合物分子通过分子间氢键作用形成一维超分子链状结构。采用循环伏安法研究了化合物2的电化学性质。     

Structural Characterization of (Arylimido)vanadium(V) Compounds with 2,6‐Difluorophenoxide Ligand

The (arylimido)vanadium(V) compound, [(p‐MeOC₆H₄N)V(OiPr)₃] was demonstrated to undergo ligand exchange reaction with one or two equivalents of 2,6‐difluorophenol, affording the (arylimido)vanadium(V) compounds, [(p‐MeOC₆H₄N)V(OiPr)₂(O‐2,6‐F₂Ph)] and [(p‐MeOC₆H₄N)V(OiPr)(O‐2,6‐F₂Ph)₂]. Their X‐ray crystallographic analyses elucidated the μ‐isopropoxido‐bridged dimeric structures, wherein each vanadium atom has a trigonal‐bipyramidal arrangement with the imido and bridging isopropoxide ligands in the apical positions. The isopropoxide ligand was selectively employed as a bridging ligand between two central vanadium atoms. On the other hand, the reaction of the (arylimido)vanadium(V) compound, [(p‐MeOC₆H₄N)VCl₃] and three equivalents of lithium 2,6‐difluorophenoxide gave the (arylimido)vanadium(V) compound, [(p‐MeOC₆H₄N)V(O‐2,6‐F₂Ph)₃]. In the crystal packing, the thus‐obtained compound showed a distorted trigonal‐bipyramidal environment at the vanadium atoms with the μ‐phenoxido‐bridged dimeric structure, wherein the 2,6‐difluorophenoxide ligand was found to serve as a bridging ligand.     

Synthesis and structural characterization of 3,4-diphenylcyclopenta-2,4-diene-1 thione and its reactivity with V(V)

In the first part of this work, we have studied the reactivity of an ethanolic solution of diphenylthiocarbazone (C₁₃H₁₂N₄S) with an aqueous solution of vanadium(V), leading to a new compound C₁₇H₁₂S (L). This compound was crystallographically characterized and identified by XRD. This technique reveals no metal in the structure. Then, we reacted L with the same metal, producing a dimeric complex V₂O₄(L)₂(H₂O)₂(OH)₂ (C1), characterized by elemental analysis, IR, UV–Visible, ¹H NMR, ¹³C NMR, and ⁵¹V NMR spectra. A probable structure has been proposed.     

SERS approach for Zn(II) detection in contaminated soil

Soil contamination by metals is a common problem encountered in many industrialized countries. In this work we present a new approach for heavy metals detection by using surface-enhanced Raman scattering (SERS) spectroscopy. Zn(II) can be clearly determined by SERS in contaminated soil by using 4-(2-pyridylazo) resorcinol (PAR) as chelating molecule for the metal ion. The SERS spectra of PAR, of its metal chelates and of the soil extract-PAR mixture were recorded using a hydroxylamine reduced silver colloid. An excellent match of the PAR-contaminated soil extracts SERS spectrum to the Zn(PAR)₂ SERS spectrum can be observed, demonstrating the presence of Zn(II) in the soil probes. Density functional theory (DFT) based calculations were also performed for a reliable assignment of SERS spectra.     

Liquid-liquid extraction and cloud point extraction for spectrophotometric determination of vanadium using 4-(2-pyridylazo)resorcinol

Liquid-liquid extraction (LLE) and cloud point extraction (CPE) of vanadium(V) ternary complexes with 4-(2-pyridylazo)resorcinol (PAR) and 2,3,5-triphenyl-2H-tetrazolum chloride (TTC) were investigated. The optimal conditions for vanadium extraction and spectrophotometric determination were identified. The composition (V: PAR: TTC) of the extracted species was 1:2:3 (optimal conditions; LLE), 2:2:2 (low reagents concentrations; LLE), 1:1:1 (short heating time;CPE), and 1: 1: 1 + 1: 1: 0 (optimal extraction conditions; CPE). LLE, performed in the presence of 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid and NH₄F as masking agents, afforded the sensitive, selective, precise, and inexpensive spectrophotometric determination of vanadium. The absorption maximum, molar absorptivity, limit of detection, and linear working range were 559 nm, 1.95 × 10⁵ dm³ mol^?1 cm^?1,0.7 ng cm^?3, and 2.2–510 ng cm^?3, respectively. The procedure thus developed was applied to the analysis of drinking waters and steels. The relative standard deviations for V(V) determination were below 9.4 % (4–6 × 10^?7 mass %; water samples) and 2.12 % (1–3 mass %; steel samples).