Dimolybdenum Pentasulphide, Mo₂S₅

Dimolybdenum Pentasulphide is obtained as a trihydrate, Mo₂S₅.3H₂O, by reducing with zinc a solution of ammonium molybdate containing more than 20 per cent, of sulphuric acid. When the solution becomes dark red it is diluted, filtered, and saturated with hydrogen sulphide, and the resulting precipitate, after successively washing with hot water, alcohol, carbon disulphide, and ether, is dried at about 70° C. The trihydrate loses one-third of its water at 140° C., but decomposes on further heating. When carefully heated in carbon dioxide, the anhydrous pentasulphide, Mo₂S₅, is obtained as an almost black compound.