Vanadium, tris structure

Reactions of these ligands have not been studied in aqueous solution. However, their complexes are readily synthesized and are stable but reactive towards heteroligands [41,42], The reported structures all show the vanadium coordinated in monomeric units after the fashion depicted in Scheme 4.9. The multidentate thiolato complexes with tri- or tetradentate functionality are sufficient to satisfy the coordination requirements of the vanadium nucleus. Structurally, the compounds are not much different from analogous complexes formed with oxygen ligands (Section 4.4.2). 

Polymerization of propylene with vanadium tris(acetylacetonate)-(C2H5)2Cl at low temperature proceeds in a living manner to give a syndiotactic polymer.153 A V-C bond of the living polypropylene end reacts quantitatively with iodine molecule to yield an iodine-polymer bond. The iodine-terminated polypropylenes of low molecular weight (Mn = 630 3200) were found by H and 13C NMR spectroscopy to have a secondary structure at the chain end.154... 

Vanadium, tris(diethyldithiocarbamato)oxy-stcrcochcmistry, 82 Vanadium, tris(dithiodibenzoyl)-Structure, 63... 

Figure 62. Structural representations of vanadium tris- and tetralds(dithiocarbamate) complexes.

The first structurally characterized triarylzincate [Li(TMEDA)2][Zn 2,4,6-(Pr1)3G6H2 3] 59 was a byproduct of the lithiation of VC13(THF)3 with Li(2,4,6-(Pr1)3C6H2)3, in which the vanadium compound had been pre-reduced with metallic zinc.116 In the solid state, the compound consists of isolated, tetrahedrally coordinated lithium ions and trigonal-planar tris(tris(isopropyl)phenyl)zincate ions. The Zn-G bonds are equidistant (2.039(7) A), but the C-Zn-C bond angles are variable, ranging from 112.2(3)° to 125.4(3)°. 

Unlike V(II), both the V(III) and V(IV) oxidation states are stable in water. However, neither the V(III) nor the V(IV) oxidation states are easily maintained in the presence of oxygen if the pH is neutral or above, although, under acidic conditions, both these states are rather easily maintained. Somewhat surprisingly, the V(IV) species is more readily oxidized by 02 than is the V(III) species. In aqueous acidic solution, the vanadium(III) ion exists as a hexaqua octahedral complex that can deprotonate to form the 2+ and 1+ species, dependent on pH. Additionally, di, tri and tetra polymeric forms are known. Structures have been proposed and their formation constants determined [10], The occurrence of the various polymeric forms in the presence of sulfate has also been described and is particularly relevant to concentration of vanadium by bioaccumulators [10],... 

Under anhydrous conditions, tetranuclear vanadium clusters such as [V404 (0CH2)3CCH3 3(0C2H5)3] can be generated in alcoholic solutions with l,l,l-tris(hydroxymethyl)ethane. The coordination does vary somewhat with the alcohol utilized in the preparation, but all retain the tetranuclear structure. Each vanadium nucleus in the complex has octahedral coordination. The clusters are not stable to hydrolysis and decompose in chloroform solution in the presence of just a few equivalents of water [5],... 

Very little work related to the insertion of ligands into the decavanadate core has been reported. Methanol, contained in aqueous solution with decavanadate, has been found to insert in a stereospecific manner in the fashion depicted in Scheme 8.3a. The situation changes dramatically for the reaction of decavanadate under forcing conditions with l,l,l-tris(hydroxymethyl)propane. This remarkable reaction does not lead to insertion into decavanadate but rather insertion into a similar decavanadium structure (Scheme 8.3b), in which all vanadiums have been reduced to vanadium(IV) [10]. 

The synthesis, properties, and biological activities of tris(maltolato)vanadium(III) and three analogues have been reported (Table 7). The structures of the [V(ma)3] complex and the ligands are shown in Figure 16. Blood glucose levels in STZ-diabetic rats were determined after 24 hours... 

Figure 16 Structure of (a) tris(maltolato)vanadium(III) and the ligands (b) maltol, (c) ethylmaltol, (d) kojic acid, and (e) 1,2-dimethyl-3-hydroxy-4-pyridinone...

Tris[bis(trimethylsilyl)amido] vanadium(III) crystallizes from benzene as dark-brown, soft needles, extremely sensitive to air and moisture. This complex is paramagnetic 2.4 BM) but does not show electron paramagnetic resonance absorption at temperatures above that of liquid nitrogen. The compound is thermally unstable but gives a mass spectrum containing the parent molecular ion. Infrared spectra and electronic absorption spectra are given in Table II. The crystalline complex has the same trigonal structure as the Fe compound. ... 

The first evidence for activation of exogenous 02 on a vanadium(TV) center was obtained recently.154 The reaction of vanadium(IV) hydroxo tris(3,5-diisopropylpyrazol-l-yl)borate with 02 resulted in the corresponding peroxo complex, which was structurally characterized and found to belong to the class of compounds illustrated in (22).154... 

Vanadium(V) mono-, di-, tri-, and tetra(phosphoraniminato) complexes (83)-(86) have been prepared and an acetonitrile solvate of [V(NPPh3)4]Cl structurally characterized.443 A tridentate pyrazolylcyclohexanol complex of vanadium(V) has also been synthesized.444 A derivatized pyridine ligand is chlorinated by VOCl3 in the presence of t-BuOOH to yield the vanadium(V)... 

A cyanohydridoborato vanadium(II) complex, tra s-[V(NCBH3)2(thf)4], has been synthesized and structurally characterized (212).858 Additional oligomeric complexes have been prepared complexes that have been characterized include trinuclear vanadium complexes,859-862 dinuclear V-Fe complexes,863 and the first tetranuclear V11 species [V4(/x3-Cl)2(M-Cl)2(M-CF3C02)2(thf)6].864 The addition of tris(pyrazolyl)borate ligand to the tetranuclear species results in the dissociation of the complex to form a neutral dimeric species [V(tpb)-(/x-Cl)(/x-CF3CO2)2V(th03] (213) in which one of the vanadium centers is facially coordinated by tpb.864... 

Among relevant studies one can cite the investigations of sulfur adsorption on molybdenum " ), silicon ), copper " ), gold ), vanadium ) and iron " ). Such examples may be found in very large number in the literature we shall try and set in evidence the general trends observed in structures resulting from sulfur adsorption on metallic surfaces. 

Other condensed vanadates, e.g. trivanadate, hexavanadate, dodecavanadate and pentadecavanadate, are known, but play minor roles in the aqueous systems (tri-and hexavanadate) or are thermodynamically unstable with respect to decavanadate (polyoxovanadates with more than 10 vanadium centres). An interesting case from the structural point of view is the tridecavanadate [Hj2Vi304q], included in Table 2.3 I 1... 

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