Formation of α- and β-Keggin-type [PW12O40]3- complexes in aqueous media

The formation process of the alpha- and beta-Keggin-type [PW12O40](3-) complexes was investigated in an aqueous 50 mM (M = mol dm(-3)) W(VI)-5.0 mM P(V) system. The P-31 NMR study confirmed the formation of A-alpha-[PW9O34](9-), A-beta-[PW9O34](9-), alpha-[PW11O39](7-), and beta(1)-[PW11O39](7-) on acidification of an alkaline solution Of WO42- and HPO42- to pH 7.5 or below. An isomeric mixture of alpha- and beta-[PW12O40](3-) was obtained on further acidification of such solutions containing both alpha- and beta-type lacunary complexes to pH 1 or below. On the other hand, heating of the W(VI)-P(V) system caused A-alpha-[PW9O34](9-), A-beta-[PW9O34](9-), and beta(1)-[PW11O39](7-) to disappear completely, leaving aIPW PW11O39](7-). Acidification of the alpha-[PW11O39](7-) solution produced only alpha-[PW12O40](3-).