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. |