Ammonium tetrathiomolybdate

Ammonium tetrathiomolybdate is the chemical compound with the formula [NH4]2[MoS4]. This bright red ammonium salt is an important reagent in the chemistry of molybdenum and has been used as a building block in bioinorganic chemistry. The thiometallate anion has the distinctive property of undergoing oxidation at the sulfur centers concomitant with reduction of the metal from Mo(VI) to Mo(IV).

Preparation and structure
The salt contains the tetrahedral [MoS4]2- anion. The compound is prepared by treating solutions of molybdate, [MoO4]2- with hydrogen sulfide in the presence of ammonia:
 * [NH4]2[MoO4] +  4 H2S  &rarr;  [NH4]2[MoS4]  +  4 H2O



Reactions
The anion is also an excellent ligand. For example, with Ni(II) sources, it forms [Ni(MoS4)2]2-. Much of the chemistry of the thiomolybdate results from studies on salts of quaternised organic cations, such as [NEt4]2[MoS4] and [PPh4]2[MoS4] (Et = C2H5, Ph = C6H5). These organic salts are soluble in polar organic solvents such as acetonitrile and dmf.

The thermal decomposition of [NH4]2[MoS4] leads to sulfides of composition MoSx (2< x< 3), which are of interest as catalysts for hydrodesulfurization.

Related compounds
Several related thio and seleno anions are known including (A = alkali metal cation, [PPh4]+, [NEt4]+) More complex tetrahedral anions include A2[MoS4-xOx] and A2[WS4-xOx]
 * A3[VS4]
 * A3[NbS4]
 * A3[TaS4]
 * A2[MoSe4]
 * A2[WS4]
 * A2[WSe4]
 * A[ReS4]

Uses
Ammonium tetrathiomolybdate was first used therapeutically in the treatment of copper toxicosis in animals. It was then introduced as a treatment in Wilson's disease, a hereditary copper metabolism disorder, in humans; it acts both by competing with copper absorption in the bowel and by increasing excretion. It has also been found to have an inhibitory effect on angiogenesis, making it an investigatory treatment for cancer, age-related macular degeneration, and other diseases featuring excessive blood vessel deposition.