Thiomolybdate , ammonium copper

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. 

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. 

The deep green crystals are converted to a red powder on grinding. The material is unaffected by air, but with water it decomposes slowly to form soluble ammonium thiomolybdate and insoluble copper(I) sulfide. The compound crystallizes in the tetragonal space group 14 with unit-cell dimensions of a = 8.000 ... 

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