Polymolybdate complexes

Mononuclear examples are dominant in the simple coordination chemistry of molybdenum(VI). This is due in part to the absence of d electrons in Movl complexes, which precludes the formation of MoVI—Mo 1 metal-metal bonds. However, note must be taken of the very large class of homo- and hetero-polymolybdates which contain polynuclear Mo. These... 

Molybdates.—Normal molybdates of the type R aMoO., exist in solution but are relatively unstable, and readily form acid salts or complex polymolybdates. Thus dimolybdates, R aMogOy, can be obtained by fusion of molybdenum trioxide with sodium or potassium nitrate trimolybdates, R gMojOio, and tetramolybdates, R Mo Oig, by heating molybdenum trioxide with an aqueous solution of sodium or potassium carbonate. Even more highly acid salts—for example, octa- and deca-molybdates—can be obtained. Solutions of normal molybdates, when treated with hj droehlorie add or nitric acid, yield a precipitate of acid molybdate this reaction does not, however, take place with sulphuric, acetic, oxalic, or tartaric acids. 

Polymolybdates of manganese have not been obtained. A large number of complex salts have been described." on the composition of which, ho%vever, differing iews have been expressed. 

The present review focuses first on actinide complexes of polymolybdates (section 2) and pol5durrgstates (section 3) that have beetr isolated and structurally characterized. There are currently no reported actinide polyvanadates, -niobates, or -tantalates. A final section (4) summarises solution studies of equilibria between actinide cations and polyoxometalate anions. 

Te and Mo partially precipitate as oxides. Se, Ag and Pd partially precipitate as metals. The rest of Mo, remaining in solution, is present as polymolybdate which does not precipitate Zr as Zr-polymolybdate, since the pH of the solution is still about 1.2. Due to the nitric oxides developed during the denitration the Pu is converted to Pu(IV) that forms stable positive charged acetato-formato-complexes, if the concentration... 

The use of EDA improves the dispersion of the molybdenum as well dispersed polymolybdate entities in spite of the presence of isolated molybdate in the impregnating solution. A more complete study of the mechanism of adsorption in presence of complexing agent should be undertaken... 

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