RAMAN STUDIES ON THE IDENTIFICATION OF ISOPOLYMOLYBDATES IN AQUEOUS-SOLUTION

Molybdenum(VI) solutions were investigated in detail by Raman spectros copy with a view to establishing the speciation of the predominant pol ynuclear species (isopolymolybdates) formed in aqueous solution. The m ost intense Raman frequencies due to asymmetric stretching vibration o f Mo=O were very sensitive to even small changes of the structure of t he isopolymolybdates. As the pH was lowered, the major Raman line show ed no gradual shift but exhibited a discrete change. Evidence was obta ined for the existence of Mo7O246- (pH 4-6), Mo3O102- (pH 3.5-5), alph a-Mo8O264-(pH 2-5). beta-Mo8O264- (pH 1.5-4), and Mo36O1128- (pH 0.5-1 .5). On the other hand, neither of Mo6O192- and gamma-Mo8O264- existed in any appreciable amount in aqueous solution.