12-Molybdosilicic Acid, H₈[Si(Mo₂O₇)₆]

12-Molybdosilicic Acid, H₈[Si(Mo₂O₇)₆].28H₂O, is prepared by decomposing the sodium salt with dilute sulphuric acid and extracting with ether. It yields transparent octahedra which melt at 47° to 55° C. to a uniform liquid. Crystallised from hot nitric acid it yields a lower hydrate with 14H₂O.

When an alkali chloride or nitrate is added to a solution of the acid, or when solutions of the tetrabasic salts are treated with hydrochloric acid, yellow salts of formula R^•₃H₅[Si(Mo₂O₇)₆].xH₂O (R^• = Na, K, Ag) are obtained. Attempts to produce the normal alkali and guanidinium salts have not been successful, but on addition of concentrated silver or mercurous nitrate solutions to a solution of the tetrabasic sodium salt, yellow crystalline precipitates, of composition Ag₈[Si(Mo₂O₇)₆].15H₂O and Hg₈[Si(Mo₂O₇)₆], are obtained.

Compounds containing vanadium, of the type R^•₆H₂[Si(Mo₂O₇)₅(V₂O₆)].xH₂O, have been described.