Abstract: The anion of tungstotantalate was synthesized for the first time as K₉TaW₁₁O₄₀·15H₂O by the reaction of soluble potassium tantalate and porous white tungstic acid in aqueous solution. The structure of the anion may be proposed reasonably to be similar to that of dodecameric anion of paratungstate, resulting from substituting of one WO group in paratungstate anion by one TaO group and leading to the formation of tungstotantalate anion according to the extreme similarity of IR and UV spectra as well as chemical behavior of these two different anions.Potassium 11-tungstotantalate is soluble in hot water and unstable in alkaline medium while the structure of anion may be considered to keep unchanged in acidic medium according to the spectrophotometrical results.

Key words: tungsten, tantalum, tungstotantalate, heteropolyacid, synthesis, white tungstic acid