Molybdenum pentavalent

Hexavalent molybdenum and tungsten, pentavalent vanadium and, to a more limited extent, niobium and tantalum form a very large number of polyoxoanions ( heteropolyanions such as [PW12O40]3- and isopolyanions such as [M07O24]6-). Unlike the polyoxoanions of the post transition elements the heteropolyanions for the most part are discrete, compact species of high... 

In keeping witii its 5d 6s2 electron configuration, tungsten forms many compounds in which its oxidation state is 6+, just as molybdenum does. It forms divalent and tetravalent compounds to about the same extent as molybdenum but its bivalent and pentavalent compounds are somewhat fewer. Its anion chemistry is closely akin to that of molybdenum. 

Mild acidification of molybdate-phosphate solutions yielded the colorless [P2Mos023]"6 anion, isolated as the sodium salt48,49 The heteropoly acid containing pentavalent antimony, H3[SbMo12O40] 48 H20, was reported to have been prepared by refluxing M/20 molybdic acid with M/75 potassium pyroantimonates°), however, more work is necessary to elucidate to exact nature of molybdenum heteropoly compounds containing antimony. 

Another class of 12-heteropoly anions involves the replacement of molybdenum by pentavalent vanadium. The molybdovanadophosphoric acids,... 

Dhas, N. A., and Gedanken, A., Characterization of sonochemically prepared unsupported and silica supported nanostructured pentavalent molybdenum oxide, J. Phys. Chem. B 101, 9495 (1997a). 

Of the rather limited number of tetravalent molybdenum and tungsten derivatives known, wre shall mention here only molybdenum disulfide (M0S2), which occurs as the ore molybdenite and the octacyano complexes Mo(CN)i 4 and W(CN) 4 which, along with their pentavalent counterparts (p. 333), represent two of the very few examples of octa-covalency. 

The pentasulphide MojSg is said to be formed as a dark brown amorphous precipitate of the trihydrate when hydrogen sulphide is passed through an aqueous solution of a pentavalent molybdenum coompound, but like all pentavalent molybdenum compounds it is unstable. 

Compounds containing pentavalent molybdenum. When a solution of ammonium molybdate and ammonium thiocjmnate is reduced electrolytically and the resulting liquid extracted with ether, all the red-colouring substances pass into the latter on adding pyridine, a compound, of composition Mo(OH)2(SCN)3(CsH5N)2, is obtained in the... 

Formally, pentavalent neutral metallocorroles have been prepared by Murakami and coworkers.The first of these was the oxomolybdenum(V) corrole derivative 2.179. ° This complex was prepared by heating free-base corrole 2.82 with molybdenum pentachloride in oxygen-free decalin (Scheme 2.1.56). Alternatively, molybdenum hexacarbonyl (Mo(CO)e) could be used as the metal source. In both cases, oxidation to the oxomolybdenum complex 2.179 was believed to occur during workup (involving chromatography on neutral alumina followed by recrystallization). In this way, complex 2.179 was isolated in c. 40% yield. Similar yields of the oxochromium(V) complex 2.180 could be achieved via the reaction of 2.82 with anhydrous chromium(II) chloride in DMF. Here too, spontaneous oxidation during workup was used to afford the formally pentavalent oxo-complex 2.180. 

Mo(CO)6 appears to take place in the interfacial region Thus, the water molecule formed in the bubble may diffuse into the interfacial region or the water molecules that are available from the atmospheric air, precursor, and solvent, and stabilize the unusual pentavalent molybdenum oxide ... 

Volumetric methods for determining columbium are rapid and fairly satisfactory since tantajum does not interfere. But tungsten, molybdenum, and titanium must be completely removed. The methods depend on the reduction of pentavalent columbium to the trivalent condition by means of zinc, then the oxidation by standard permanganate. Taylor s method3 makes the reduction in a Jones reductor and the titration in an atmosphere of C02. Levy s method4 carries out the reduction and titration in an atmosphere of hydrogen in a conical flask from which the air is excluded. 

Trivalent uranium ion reduces water to hydrogen. Hence, stable aqueous solutions of trivalent uranium compounds cannot be prepared. Compounds of tetravalent uranium are generally similar to those of zirconium or thorium, except that some uranium compounds can be oxidized to the hexavalent form. Compounds of pentavalent uranium are of little importance because they disproportionate readily into tetravalent and hexavalent forms. The properties of hexavalent uranium are generally similar to those of hexavalent molybdenum or tungsten. In aqueous solution hexavalent uranium forms the uranyl ion UO2 ... 

Reports on the marine chemistry of niobium (Nb) and tantalum (Ta) are limited to one study in the Pacific Ocean. Niobium and tantalum are pentavalent metals that are predicted to exist in sea water either as hydroxides (Nb(OH)5, Nb(OH)g, Ta(OH)5 and Ta(OH)g ) or possibly as oxyacids, similar to molybdenum and tungsten. Their distributions are not conservative like those of molybdenum and tungsten, but they may not be as particle-reactive as the other hydroxide-dominated species discussed. Dissolved niobium is low in the surface (3.0pmolkg ) and... 

Potassium octacyanomolybdate(IV) may be prepared by the action of potassium cyanide upon certain tri-, tetra-, or pentavalent derivatives of molybdenum. The latter are obtained by chemicaP" or electrochemicaP reduction of molybdic acid. 

The complex oxide K4MogPi2052 contains pentavalent molybdenum and is built from MoOg octahedra and PO4 tetrahedra which share corner O atoms. The structure contains one-dimensional... 

At pH a 4,5 the reduction process gives the a and 3-products with 6 e below pH 4,5 they undergo disproportionation into compounds with 4 e" and pentavalent molybdenum. 

Henry and Van Lierde developed a three-compartment cell equipped with an reticulated vitreous carbon cathode mixed with ion-exchange resin and two Ti—Pt anodes separated by a Daramic diaphragm to selectively separate the vanadium from molybdenum (Henry Van Lierde, 1998). In this designed membrane reactor, the pentavalent vanadyl anion was selectively desorbed with respect to molybdenum after its reduction to a tetravalent vanadyl cation. Consequently, 93% vanadium recovery yields were obtained. 

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