Heteropoly Anions Series

The 12-heteropolymolybdates are apparently subdivided into two series. The structure of Series A anions i built around a central X04 tetrahedron and the anion contains 40 oxygen atoms1). Series B is typified by the 12-molybdocerate(IV) anion, [CeMo12042] 8, in which there are 42 oxygen atoms present within the anion89-92) and in which the coordination about the cerium atom is twelve-fold92). The 12-molyb-dothorate(IV) anion may have the same structure. 

The Series A 12-acids and their salts are the best known of all heteropolymolybdates and heteropolytungstates and the only compounds of this type used thus far on a large commercial scale. 

The 12-heteropolymolybdates reported earlier to contain manganese and boron as the central atoms probably do not exist93,94). 

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Tables 2 and 3 illustrate the principal series of heteropolymolybdates and heteropolytungstates, respectively, which have been reported. Table 4 represents central atoms that form heteropoly anions, the composition and structure of which have not yet been elucidated.

Most free acids of 12-heteropoly anions of Series A form isomorphous 30-hydrates. These melt in their own water of hydration at 40 to 100 °C. They begin to lose water in dry air and give up almost all 30 molecules in vacuum over sulfuric acid. The transition metal salts of the 12-molybdophosphoric and 12-molybdosilicic acids lose water up to 300 °C5 The hydrated free acids may be converted to the anhydrous H3[PMoi204o] and H4[SiMo1204o] by heating at 180 °C, the products thus obtained can be rehydrated at room temperature5. The hydrated acids... 

Mixed heteropolymolybdates and tungstates are present in the 6-heteropoly series. The synthesis of the ammonium salts of the 6-heteropoly anions with nickel as the central atom of the general formula (NH4)4[NiMo6 nWn024H6] has been reported187). All compounds thus obtained are light blue. The preparation of the free acids has also been described187). 

The structure of the series A 12-molybdo and 12-tungs o-heteropoly anions of general formula Xn +Mo12O40] <8-n>-... 

The heteropoly anions have complex structures based on the cuboctahedron (Figure 5.47). Two main series of W compounds were originally characterised, based on ions with the formula PW12O40 and P2WigOg2. 

The Series B of 12-heteropoly compounds is typified by the anion [CeMoi2042]-8, the structure of which has been determined in the salt... 

Heteropolyacids are polyoxometalates incorporating anions (heteropolyanions) having metal-oxygen octahedra as the basic structural units. Among a wide variety of heteropoly acids those belonging to the so-called Keggin series are the most important for catalysis. They include heteropolyanions where X is the central atoms (P, Si , etc.), y... 

This section will focus exclusively on self-exchange reactions between the iso-structural series of Keggin-type heteropoly tungstates, X +Wi2O40 " , X + = P + (anion 1), Si" + (anion 2), Al + (anion 3) and y = 8,9,10 for the fully oxidized, one-and two-electron reduced species, respectively. These electronic states are indicated... 

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