I Ammonium Tetrathiomolybdate VI

Lionetti, G. Allegra, and A. Immirzi, Chem. Commun., 1965, 336. 

When hydrogen sulfide is passed into a strongly ammoniacal solution of copper(II) and molybdate(VI) ions, the initial copper-(II) sulfide precipitate is redissolved, the copper is reduced to the copper(I) state by sulfide ion, and the compound CuNH4MoS4, copper(I) ammonium thiomolybdate(VI), precipitates. The compound has been reported previously by Debray,1 who was unable to characterize it. The following method of preparation is based upon Debray s work and gives superior yields and higher purity. 

The procedure should be carried out in an efficient fume hood. A solution of ammonium hydrogen sulfide is prepared by saturating a concentrated ammonium hydroxide solution with 

A black precipitate appears which dissolves almost immediately to form a deep-red solution. The solution is boiled with stirring for 2-4 minutes, during which time a crystalline precipitate forms, which appears green in reflected light and purplish-red in transmitted light. The precipitate is filtered under suction and washed with 30 ml. of concentrated ammonia followed by 30 ml. of water and finally with 30 ml. of ethanol. It is then allowed to dry in air and finally in a desiccator. Yields of product range from 14.4 to 17.6 g. (79-96%). 

Alternatively, the compound can be obtained by letting the deep-red solution, obtained after mixing the solutions, stand at room temperature for 2-4 hours. In this case the product is usually contaminated with crystals of ammonium tetrathio-molybdate(VI), (NH4)2MoS4. The compound also can be obtained in poor yields by dissolving freshly precipitated copper(II) sulfide in ammoniacal ammonium molybdate solution saturated with hydrogen sulfide. Undissolved copper(II) sulfide is removed by filtration after 3-5 minutes, and the copper(I) ammonium thiomolybdate(VI) is obtained by boiling as above. 

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