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 .     

Voltammetrische und spektroskopische Untersuchungen zur Komplexbildung von Vanadium(IV) und Vanadium(V) mit Carbonat

Voltammetric and Spectroscopic Investigation of Complexation of Vanadium(IV) and Vanadium(V) by Carbonate Solutions which contain in addition to vanadium(IV) or vanadium(V), respectively, a high excess of bicarbonate or carbonate were studied by voltammetric and spectroscopic methods. A reversible electrode reaction occurs in the pH range 7–8 in 1 M KHCO₃. While generating V^IV from V^V electrochemically a carbonate ligand is added to V^IV. Based on ESR parameter recorded at room temperature and 77 K the existence of a V^IV carbonato complex is suggested. A comparison of these ESR parameter with those of analogous V^IV complexes leads to conclusions in view of the structure of the V^IV carbonato complex. These structural suggestions are supported by the fact that V^IV and V^V form a mixed valent dimer in HCO₃^?/CO₂-buffer of pH 7.5. Such dimers can be formed only when one of the oxygens of the V^VO₂⁺ cis-dioxo unit is able to coordinate at a basal site in the V^IV-complex. Thus, conclusions regarding the arrangement of the carbonato ligands in the monomeric V^V complex are possible too. A comparison of the complexes which are formed by V^IV and V^V with carbonate and the adducts arising from the interaction of V^IV and V^V with transferrin reveals the similarities of the both redox couples.     

Zur Bestimmung von Vanadium(IV)

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Vanadium (V, IV) und Uran (VI)

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Determination of Vanadium(V) and Vanadium(IV) in Bismuth- and Copper-Containing Compounds by Controlled-Potential Coulometry

It was shown that vanadium(V) and vanadium(IV) can be determined at a large Pt electrode in H₂SO₄ solutions in the presence of copper and bismuth by controlled-potential coulometry with RSD no worse than 0.2%. Compounds of the composition Bi₄V_1.8Cu_0.2O_{10.7 – x} were analyzed.     

Determination of Vanadium(IV) and Vanadium(V) in Benfield Samples by IEC with Conductivity Detection

In this study, the determination of vanadium valence state, V(IV) and V(V) has been achieved using ion-exchange chromatography with conductivity detector. In this method, V(IV) was determined as V(IV)-EDTA complex and V(V) as vanadate ion. Determination of V(IV) was successfully done using 3 mM carbonate/bicarbonate/EDTA at pH 8.6 as the eluent. The additive, EDTA in the mobile phase did not seem to interfere with the V(IV) analysis. The detection of V(V) was achieved with 5 mM disodium hydrogen phosphate buffer at pH 10.4. A linear calibration graph over VO₃ ^? and V(IV) with concentration ranges 5–15 mg L^?1 gave the detection limit at 0.09 and 0.1 mg L^?1, respectively. Both V(IV) and V(V) were successfully determined in Benfield sample, with concentrations of V(IV) and V(V) at 4 and 11,000 mg L^?1, respectively.     

Vanadium(IV) und Molybd?n (V)

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钒(Ⅴ)-三溴偶氮胂-溴酸钾催化动力学光度法测定钒

1 引言 钒是人体不可缺少的微量元素之一.适量的钒有利于身体健康,但含量过低或过高都会引起某些器官的病变而出现不适的症状,因而对其准确的测定具有重要的意义.近年来,用催化光度法测定钒引起了人们的广泛兴趣.     

Vanadium(II) complexes of aromatic diamines

The new vanadium(II) complexes [V(opd)₄]X₂ and [V(mopd)₄]X₂, where opd = o-phenylenediamine, mopd = 4-methyl-o-phenylenediamine, and X = Cl or Br, have been prepared by reaction of the aromatic diamine with the vanadium(II) halide in EtOH. Magnetic measurements suggest that these contain octahedral vanadium(II) complex cations, and this is confirmed by the diffuse reflectance spectra. I.r. spectra suggest that the [V(opd)₄]²⁺ cations contain two bidentate and two monodentate diamine ligands.     

Zur photometrischen Bestimmung von Vanadium(IV)

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Vanadium(III) complexes of salicylaldehyde thiosemicarbazones

Hexacoordinate complexes of vanadium(III) containing tridentate ONS chelating substituted salicylaldehyde thiosemicarbazones have been prepared and characterised by elemental analysis, i.r. and u.v.–vis. spectroscopy and cyclic voltammetry.     

Vanadium(V) Sorption by Organosilicon Polymers

Features of vanadium(V) sorption by cross-linked organosilicon polymers-polyorganylsilsesquioxanes containing acetamide, phthalamide, malondiamide, and thiourea dioxide functional substituents, were studied.     

Spectrophotometric Investigation of Vanadium (V)-N-Pyridylaminothioformyl-N'-phenylhydroxylamine

The pink complexes of vanadium (V) and N-pyridylaminothioformyl-N′-phenylhydroxylamine are extractable into chloroform. Spectrophotometric studies show that the 1:2 complex predominates in the acidity range of 2.5-6 N HCl. The values of the stability constants, stepwise and overall, have been calculated following extended Yatsimirskii, Leden and Harvey-Manning methods.     

Zur spektralphotometrischen Bestimmung von Vanadium (IV)

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Vanadium(V), Cer(IV) und Chrom(VI)

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Die potentiometrische Titration von Vanadium (V)

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Amperometrische Bestimmung von Vanadium(IV) und Titan(IV)

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Vanadium(III) and vanadium(V) amine tris(phenolate) complexes

The coordination chemistry of amine tris(phenolate) ligands around V(III) and V(V) is described for the first time. Three amine tris(phenolate) ligands were employed featuring different steric and electronic influence exerted by the phenolate substituents in the ortho and para positions being either t-Bu, Me, or Cl. V(III) complexes of all ligands (1-3) were readily obtained by reaction between the ligand precursors and VCl3(THF)3 in the presence of triethylamine. The complexes obtained were pentacoordinate, a THF ligand completing the coordination sphere of the metal, which was found to be of almost perfect TBP geometry, as revealed by crystallography. V(V) oxo complexes of all the ligands (4-6) were readily obtained by a reaction between the ligand precursors and VO(OPr)3. The oxo complexes of the alkyl-bearing ligands (4 and 5) could also be synthesized by the air oxidation of the corresponding V(III) complexes (1 and 2); however, the attempted air oxidation of the V(III) complex bound to the electron-poor ligand (3) did not yield the corresponding oxo complex 6. 1H NMR and crystallographic analysis of complexes 4 and 5 supported their TBP structures. Complex 6, on the other hand, was found to be composed of a TBP complex (6a) and an octahedral complex (6b) in equilibrium, the octahedral complex being more stable at lower temperatures. An X-ray structure of 6b revealed a mononuclear oxo complex, the sixth coordination site being occupied by an aqua ligand to which two THF molecules are H-bonded. Complexes 4-6 catalyze the epoxidation of olefins by t-BuOOH, albeit slowly. These complexes may thus be considered as structural and functional models of vanadium-dependent haloperoxidase enzymes.