Vanadium complexes oxalates

A number of ternary complexes with simple dicarboxylic acid complexes supported by other ligands have been reported. These include the mixed valence Viv,v complex with 2,2 -bipyridine (bpy) as the supporting ligand134 and the dinuclear vanadium(V) oxalate-bridged complex.135 The structure-reactivity relationship in the redox series Vv,iv ni chelated to 2-ethyl-2-hydroxybutanate... 

Scheme 5.8 Insulin-mimetic vanadium complexes. In the peroxovanadate complex, L = bipyridine (bipy), oxalate (ox), phenanthroline (phen) and picolinate (pic). BMOV represents bis(maltolato)oxovanadium(IV).

If a 1 1 molar ratio of a solution of the chloride of the cobalt complex anion and a solution of the potassium salt of the vanadium complex are mixed, a precipitate is formed and it can be analysed for combined (V+ oxalate) and for cobalt. This can be carried out to verify its formula. 

Weigh out about 2.67 g of the cobalt complex and dissolve in 60 cm water. Weigh out about 4.77 g of the vanadium complex (Sec. 10.3.2) and dissolve it in 100 cm water and add the solution slowly with stirring to the cobalt complex solution. Allow to stand in an ice bath until precipitation seems complete. Filter under suction and wash on the filter with small volumes of ethanol. Dry by continued suction while pressing between filter paper. Analyse for (V+ oxalate) using standardised permanganate (Sec. 10.3.2) and for cobalt as above in trisoxalatocobaltate(Ill). Assign a formula to the product. 

Values for the formation constants of [V(C204)]+ and [V(C204)2] were respectively 1.6 x 107 and 3.5 x 1012.271 By irradiation of these solutions at 254 nm, there is a photodecomposition of the oxalate sensitized by the oxalato vanadium(III) complex the resulting products were equimolar amounts of CO and C02. K3[V(C204)3]-3H20 can be easily crystallized from aqueous solutions containing ammonium vanadium alum and potassium oxalate. The measured magnetic moment is 2.78 BM and this compound obeys the Curie law quite closely.272 The thermal decomposition has been studied.273... 

Vanadium(V) oxide is amphoteric, dissolving in alkali to give salts of tetrahedral VO " anion, and in acid to give V02. The latter cation is almost certainly cis-[V02(H20)4]+, as in [V02(ox)2]3- and [V02(edta)]3 (ox = oxalate dianion edta = ethylenediamine tetraacetate tetraanion). All dioxo complexes of d° metals have cis configurations, an arrangement that maximizes dji-pjt interactions. 

When an electrolyte which is without action on vanadium at ordinary temperatures (for example, dilute solutions of mineral acids, of oxalic acid, or of potassium halides) is electrolysed with a vanadium anode, a complex tetravalent vanadium ion is produced. Similarly, electrolysis at 100° C. and in molten chlorides of sodium or zinc gives rise to complex tetravalent vanadium ions. The E.M.F. in each case is found to be independent of the nature of the electrolyte. When, however, solutions of caustic soda or of caustic potash are employed, the vanadium dissolves as a pentavalent ion, irrespective of variations... 

Somewhat surprisingly, maltol (2-methyl-3-hydroxy-4-pyrone), an aromatic analogue to a-hydroxy carboxylic acids, shows little inclination toward formation of dimeric complexes. Rather, the chemistry is more in parallel with that of oxalate, and an x-ray structure of the bismaltolato complex [25] shows a cis octahedral coordination similar to that found for the oxalate complex. Under mildly acidic to moderately basic solution, the major complexes are mono- and bisligand derivatives. The corresponding vanadium chemical shifts are -509 and -496 ppm, respectively [25,26], The closely related amines, 2-methyl-3-hydroxy-4-pyridinone and its N-... 

Vanadium, the first element in Subgroup oA, and neighbour to chromium, is found in association with molybdenum in certain complex compounds. For example, when boiling solutions of molybdo-oxalates react with vanadium pentoxide, crystalline products are obtained which are thought to be substituted vanadates containing the complex anion... 

The diphenylcarbazide method is almost specific for chromium(Vl). Interferences result only from Fe, V, Mo, Cu, and Hg(II) present at much higher concentrations than the chromium. Iron(lll) can be masked by phosphoric acid or EDTA. Iron(III) can also be separated as Fe(OH>3, after chromium has been oxidized to Cr(VI), or by extraction. Vanadium can be separated from Cr(VI) by extraction as its oxinate at pH -4. Molybdenum is masked with oxalic acid, and Hg(II) is converted into the chloride complex. 

Tungsten, molybdenum, and vanadium interfere in the determination of niobium. In contrast to the corresponding tungsten complex, the niobium-thiocyanate complex is decomposed by oxalic acid. Fe(ni), U, Ti, and Ta do not interfere if they are present in no greater than hundred-fold amounts relative to niobium. Phosphate and fluoride interfere, but the latter can be masked with aluminium ions [37]. 

Vanadium (V, at. mass 50.94) occurs in the V, IV, III, and II oxidation states, vanadium(V) compounds being the most stable. In alkaline medium, the colourless vanadate VOs ions exist, whereas in strongly aeidic media, the yellow V02 cations are present. Within the intermediate pH range polymerized orange-yellow anionic forms occur. Vanadium(V) forms heteropoly acids with P(V), Mo(VI), and W(VI), and also peroxide complexes. Vanadium(IV) occurs as the blue vanadyl ion V02", stable in acid solutions and readily oxidized to vanadium(V) in alkaline solution. The VO cation is amphoteric. At pH 4, V0(0H)2 precipitates and at pH 9 it dissolves. Vanadium(IV) forms fluoride-, oxalate-, and... 

The mechanism of reaction (Scheme 5) involves the proton equilibrium of vanadium(v), followed by reaction with the hydrated form of the a-keto-acid. The values K=3A (35 °C) and 2.0 (30 °C) have been derived kinetically. Initial oxidation of glyoxylic acid to oxalic acid is ruled out in view of the complex reaction of the latter with V. A study has been made, however, of the oxalic acid catalysis of the oxidation of iodide by vanadium(v). ... 

Sulfate, oxalate, and tartrate form complex ions with pentavalent vanadium in aqueous solution. Oxalate complexes are stable to the point that only in the presence of excess oxalate does a precipitate form upon addition of solutions containing calcium salts. 

Tetravalent vanadium forms a large number of complexes, all of which involve the vanadyl group, VO, and most of which are ato- complexes. The most common oxalato complex is H2(V0)2(C204)3, which can give a positive test for the presence of the oxalate ion in aqueous solutions. Aqueous solutions of the pure monovanadyl complex do not test for the presence of the oxalate ion. Complexes of sulfate and sulfite analogous to the oxalate complexes have been observed [4]. Ducret [5] suggested the existence of weak fluoro complexes at a pH of approximately 3. A tartrate and two citrate complexes can also be formed with the vanadyl ion. 

Three general classes of vanadium-containing compounds are of interest for their utility as insulin-mimetic agents (1) inorganic vanadium salts, both anionic (vanadates [V04] ) and cationic (vanadyl VO +) (2) complexes resulting from combination of vanadium(V) and hydrogen peroxide(s) (mono- and di-peroxovanadates, [V0(02 )(H2O)2(L-0f ( =0,1,2) and [V0(02)2 (L-Oj ( = 1,2, 3, and L = e.g., bipyridil, oxalate, phenanthroline, picoli-nate), and (3) chelated vanadium(IV) complexes (Scheme 5.8) [160], Vanadyl,... 

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