9-Tungsto-arsenates

Tungsto-arsenic Acids and Tungsto-arsenates.—These compounds are analogous to the phosphotungstic acids and their salts (see this Series, Vol. VII, Part III), but the complex anions are... 

Vanado-arsenates.—These compounds are analogous to the molybdo- and tungsto-arsenates (see pp. 214, 229). They are derived from the hypothetical arseno-aeid H-[As06]. The salts which have hitherto been prepared are all of low vanadium pentoxide content compared with the amount of arsenic pentoxide present, and correspond therefore to the luteo vanado-phosphates (see Vol. VI, Part III). Three series are known. The first has the general formula 2R 0.V20s.As205. 

Tungsto-arsenates.—Only the ammonium salt, XH4)3H has been prepared. It separates as a white crystalline precipitate when a solution containing normal sodium tungstate... 

Tungsto-vauadoarsenophosphates.—Several ammonium salts have been prepared, which are most probably isomorphous mixtures of arsenates and phosphates.2... 

The use of heteropoly anions as catalysts, however, was not new for the Eni researchers involved in oxidation chemistry. Some very peculiar heteropolyanions had been discovered at the Istituto Donegani at the beginning of the 1980s. Basically, they were quaternary ammonium (or phosphonium) salts of a new class of peroxidic tungsto-phosphates or arsenates in which the W (or Mo) to P (or As) ratio was as low as four the best known, a typical example of this class, is the PW4O2J anion, which was also the first peroxidic derivative of a heteropolyacid whose structure was solved. Both the free acid and the reduced forms of these heteropolyanions are unstable, and it was not possible to isolate them. 

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