Vanadium compounds chemical properties

Since the discovery of hexacarbonylvanadium(O) and hexacarbonylvanadate( 1-) by Calderazzo and co-workers in 1959 and 1960, these substances have been key precursors to a variety of vanadium compounds, including inorganic noncarbonyl species, organovanadium complexes," and other vanadium carbonyls. Neutral V(CO)6 is of special interest in that it is the only isolable 17-electron homoleptic metal carbonyl and exhibits fascinating chemical properties that are often reminiscent of iodine and classic pseudohalogens. ... 

Polyhydroxy compounds are oxidized by such metal ions as vanadium(V), chromium(VI), cerium(IV), iridium(IV), and gold(III), among others. These oxidations were found to be catalyzed by acids.171 173 Vanadium(V) and chromium(VI) are closely related in their chemical properties, but the reduction of V(V) is difficult compared with that of Cr(VI) because of its lower redox potential [V(V)-V(IV) = 1.00 V Cr(VI)-Cr(III) = 1.20 V], However, the redox potential increases at lower pH values, facilitating the oxidation of sugars. 

The vanadium silicalites (with MFI and MEL stmcture) are active oxidation catalyst in gas and liquid phase reactions [180]. As for the titanium silicalites, only the ftamework associated vandium exhibits redox properties [181]. For example, in the hydroxylation of phenol, silicalite impregnated with vanadium compounds is catalytically inactive [182]. The catalytically active vanadium species is speculated to be located in non-tetrahedral positions, most probably chemically bound to the framework. Vanadium bound in that way is not extractable from the lattice [ 183]. A proposed stmcture of the vanadium site is schematically shown in Scheme 21. Note that the Si-O-V bonds are longer than the Si-O-Ti bonds and that V seems to be more exposed. The redox properties are affiliated with the changes in the oxidation state of vanadium between +IV and +V. Vanadium silicates with SiA ratios ranging from 40 to 160 have been reported and these high values suggest (in accordance with V MAS-NMR measurements) that the V sites are isolated in the lattice. 

If the trace element and the collector have opposite chemical properties (acidic, basic), the co-precipitation may be the result of formation of chemical compounds. For example, traces of germanium or vanadium form germanates or vanadates in co-precipitation with Fe(III)-, A1-, or La- hydroxides, while traces of tungsten or molybdenum, on co-precipitation with Fe(III) hydroxide, form the corresponding Fe(III) tungstate or molybdate. 

The physical and chemical properties of various vanadium compounds are shown in Table 3-2. 

TABLE 3-2. Physical and Chemical Properties of Vanadium and Compounds ... 

Physical and Chemical Properties. The physical and chemical properties of vanadium and its compounds are reasonably well documented (see Tables 3-1 and 3-2). Further information, such as partition coefficients, would be helpful in understanding the transport and transformation of vanadium in the environment. 

Oxidation States One of the most characteristic chemical properties of the transition metals is the occurrence of multiple oxidation states. For example, in their compounds, vanadium exhibits two common positive oxidation states, chromium three, and manganese three (Figure 22.5A), and many other oxidation states are seen less often. The ns and (n — l)d electrons are so close in energy that transition elements can use all or most of these electrons in bonding. This behavior is markedly different from that of the main-group metals, which display one or, at most, two oxidation states in their compounds. 

Shiny silvery metal that is relatively soft in its pure form. Forms a highly resistant oxide coat. Used mainly in alloys, for example, in construction steel. Tiny amounts, in combination with other elements such as chromium, makes steel rustproof and improves its mechanical properties. Highly suited for tools and all types of machine parts. Also applied in airplane turbines. Chemically speaking, the element is of interest for catalysis (for example, removal of nitric oxides from waste gases). Vanadium forms countless beautiful, colored compounds (see Name). Essential for some organisms. Thus, natural oil, which was formed from marine life forms, contains substantial unwanted traces of vanadium that need to be removed. 

In addition to vanadium, other early transition metals have been shown to have antidiabetic properties, which is not surprising, as this class of compounds would be expected to share some chemical functionality. Chromium [110-112], tungsten [113,114], and molybdenum [115,116] all have demonstrated insulin-like properties. 

This review analyzes the properties which are necessary for heterogeneous catalysts to promote the oxyfunctionalization of light paraffins to valuable chemicals. Three catalytic systems are discussed i) vanadium/phosphorus mixed oxide, the industrial catalyst for the oxidation of n-butane to maleic anhydride, which is here also examined for reactions aimed at the transformation of other hydrocarbons ii) Keggin-type heteropolycompounds, which are claimed for the oxidation of propane and isobutane, whose composition can be tuned in order to direct the reaction either to the formation of olefins or to the formation of oxygenated compounds iii) rutile-based mixed oxides, where rutile can act as the matrix for hosting transition metal ions or favour the dispersion of other metal oxides, thus promoting the different role of the various elements in the formation of acrylonitrile from propane. 

The class of layered transition metal dichalcogenides has been of great interest because of their varied electronic properties and chemical reactions. Most compounds of this class may be prepared by stoichiometric reactions of the elements above 500°. However, the highest vanadium sulfide that can be made in this manner is VjSg. An amorphous VS has been prepared by the metathetical reaction of LijS and VC. The method presented here allows preparation of polycrystalline VSj with the Cdiz structure. ... 

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