Potassium Thiodimolybdate, K₂Mo₂S₇

Potassium Thiodimolybdate, K₂Mo₂S₇, is obtained as a dark grey substance on addition of a deficiency of mineral acid (preferably acetic acid) to an aqueous solution of the normal thiomolybdate and evaporation of the brown liquid.

The compound K₆Mo₂S₉ results from the passage of hydrogen sulphide through a 5 per cent, solution of normal potassium molybdate containing a sufficient excess of potash. The aqueous solution is orange-yellow in colour.