Heteropoly Acids and Their Salts

FIGURE 5.46 Structure of potassium antimonophosphate K2ShPOg. ShO octahedra linked to PO4 tetrahe-dra, K+ between chains, (a) View down chain direction (b) view of chains in elevation. 

Orthophosphates can be detected analytically by the yellow precipitate of ammonium phospho-molybdate which is obtained when their solutions are mixed with a solution of ammonium molybdate in nitric acid (Chapter 14.1). 

The so-named heteropoly anions all contain finite cavities. This is in contrast to structures discussed elsewhere in this section which frequently contain extended cavities or channels, formed between the MOg octahedra (M = Mo, W, V, Nb, Ti, etc.) and the PO4 tetrahedra. 

The structure of the first was worked out by Keggin [72] in 1934, and that of the second by Dawson [73] in 1953. In these structures, W can be replaced by Mo or V and occasionally by other atoms moreover, the P atoms may be replaced not only by As, but also by Si, Ge or B, to give iso-structural (but less stable) anions such as AsWjjO, SiWjjO, BWjjO q and so on. 

Heteropoly anions based on W and P are generally the most stable and appear to exist in greatest variety (Tables 5.33 through 5.35). Most of the add structures decompose at 300-500°C. The anion PW,204o is generally more stable than PMo,204o and this is reflected in the decomposition temperatures of the solid acids  

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Iso- and heteropoly acids and their salts HgWcQu, K P(MojOio) ... 

We shall be concerned in this chapter with the clathrate hydrates and the hydrates of salts, acids, and hydroxides. The structures of zeolites are described in Chapter 23, as also are the clay minerals, which can take up water between the layers. Examples of hydrated basic salts and of hydrates of heteropoly acids and their salts are also discussed in other chapters. 

Heteropoly acids and their salts are formed when molybdate and tungstate solutions containing other oxoanions (e.g., P043- and Si044-) or metal ions are acidified. At least 35 elements are known to be capable of functioning as the hetero atoms. 

Heterogeneous catalysts that exhibit good characteristics are silica-supported mixed Mo-V heteropoly acids and their Pd salts,1317 Pd on titania,1318 supported H3PMO12O40, and heteropoly acids and salts with Pd(OAc)21320 or PdCl2.1321... 

Heteropoly acids and their cesium salts Redox behavior He, 02, and He/HzO... 

Between 35 and 40 heteroatoms are known to form heteropoly anions and their corresponding acids. Large heteroaloms such as Ceoctahedra share faces to form MojGg groups which are corner connected to each other.39... 

The constitution of many of the heteropoly-acids and of their salts may thus be explained, although direct proof of the correctness of some of these formulae is lacking. Some of the heteropoly-compounds of vanadium are, however, very complex, and cannot be represented by application of the foregoing scheme. To take an extreme instance, Rogers1 prepared a black, crystalline compound to which he ascribed the following formula —... 

The evidence for the formation of complex heteropoly-acids with tantalic acid is very comparable to that set forth in the case of niobic acid (see p. 165). Solutions of tantalates are readily hydrolysed in aqueous solution by boiling, and even more readily by the addition of mineral acids, acetic acid or succinic acid in the presence, however, of arsenious add, arsenic add, tartaric add or dtric add no precipitation of tantalic add takes place. Again, tincture of galls yields a yellow predpitate with solutions of tantalates which have been rendered feebly acid with sulphuric add this reaction does not, however, take place in the presence of ordinary tartaric add, racemic add or citric acid. Tartaric add also prevents the formation of the predpitates which are thrown down on the addition of potassium ferrocyanide or potassium ferricyanide to faintly acid solutions of tantalates, and hinders the precipitation of tantalic add from solutions in inorganic acids by the action of ammonia. In all these cases it is assumed that complex acids or their salts are produced, in consequence of which the usual reaction does not take place. 

The copolymerization between trioxane and suitable comonomers (ethylene oxide, 1,3-dioxolane, diethylene glycol formal, 1,4-butane diol formal in amounts of 2-5% by weight) is performed using cationic initiators. The cationic initiators could be Lewis acids, such as BF3 or its etherate BF3Bu20 which was used, for example by Celanese (the mechanism of this reaction was studied in detail [163,164]) or protic acids such as perchloric acid, perfluoroalkane sulfonic acids and their esters and anhydrides. Heteropoly acids were used and also a series of carbenium, oxocarbenium salts, onium compounds, and metal chelates. To regulate the molecular weight chain-transfer agents, such as methylal and butylal, are added. 

Catalysis by heteropoly compounds. III. The structure and properties of 12-heteropoly-acids of molybdenum and tungsten (HjPMOjj and their salts pertinent to heteroge-... 

Misono, M., Mizuno, N., Katamura, K., Kasai, A., Konishi, Y., Sakata, K., Okuhara, T., Yoneda, Y. 1982. Catalysis by heteropoly compounds. HI. The structure and properties of 12-heteropoly acids of molybdenum and tungsten and their salts pertinent to heterogeneous catalysis. Bulletin of the Chemical Society of Japan 55(2) 400-406. 

Heteropolyanions are polymeric oxoanions which are formed by the condensation of more than two different oxoanions (e.g., eq.(l)). Polyanions consisting of one kind of oxoanions are called isopolyanions. The term heteropoly compounds is used to indicate heteropoly acids (free acid forms) and their salts. 

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