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

The formation process of the α- and β-Keggin-type [PW 1 2 O 4 0 ] 3 - complexes was investigated in an aqueous 50 mM (M = mol dm - 3 ) W(VI)-5.0 mM P(V) system. The 3 1 P NMR study confirmed the formation of A-α-[PW 9 O 3 4 ] 9 - , A-β-[PW 9 O 3 4 ] 9 - , α-[PW 1 1 O 3 9 ] 7 - , and β 1 -[PW 1 1 O 3 9 ] 7 - on acidification of an alkaline solution of WO 4 2 - and HPO 4 2 - to pH 7.5 or below. An isomeric mixture of α- and β-[PW 1 2 O 4 0 ] 3 - was obtained on further acidification of such solutions containing both α- and β-type lacunary complexes to pH 1 or below. On the other hand, heating of the W(VI)-P(V) system caused A-α-[PW 9 O 3 4 ] 9 - , A-β-[PW 9 O 3 4 ] 9 - , and β 1 -[PW 1 1 O 3 9 ] 7 - to disappear completely, leaving α-[PW 1 1 O 3 9 ] 7 - . Acidification of the α-[PW 1 1 O 3 9 ] 7 - solution produced only α-[PW 1 2 O 4 0 ] 3 - .