Ammonium tetrathiomolybdate

Ammonium tetrathiomolybdate

Names
Other names ammonium thiomolybdate
Identifiers
CAS Number	15060-55-6 Y
ChemSpider	10764593 Y
Jmol 3D model	Interactive image
RTECS number	QA4668250
InChI InChI=1S/Mo.2H3N.4S/h;2*1H3;;;;/q;;;;;2*-1/p+2 Y Key: PQNOIAHNKHBLRN-UHFFFAOYSA-P Y InChI=1S/Mo.2H3N.4S/h;2*1H3;;;;/q;;;;;2*-1/p+2 Key: PQNOIAHNKHBLRN-UHFFFAOYSA-P
SMILES [NH4+].[NH4+].[S-][Mo]([S-])(=S)=S
Properties
Chemical formula	H8N2MoS4
Molar mass	260.28 g/mol
Appearance	red crystals
Melting point	decomp ~ 155 °C
Basicity (pKb)	decomposes
Structure
Crystal structure
Vapor pressure	{{{value}}}
Related compounds
Related compounds	(NH4)2[WS4], MoS2
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Ammonium tetrathiomolybdate is the chemical compound with the formula [NH₄]₂MoS₄. 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 → [NH₄]₂[MoS₄] + 4 H₂O

File:MoS4.png

The [MoS₄^]2− anion.

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 molybdenum trisulfide (MoS₃), ammonia (NH₃) and hydrogen sulfide (H₂S), beginning at 155 °C till 280 °C.

(NH₄)₂(MoS₄) → MoS₃ + 2 NH₃ + H₂S

MoS₃ then decomposes again to molybdenum disulfide (MoS₂) in a broad temperature range from 300 °C to 820 °C. Perfect decomposition to MoS₂ under inert gas requires at least 800 °C according to the following reaction,

MoS₃ → MoS₂ + S

but it can also be achieved at 450 °C, if there is enough hydrogen.

MoS₃ + H₂ → MoS₂ + H₂S

Related compounds

Several related thio and seleno anions are known including (A = alkali metal cation, [PPh₄]⁺, [NEt₄]⁺)

• A₃[VS₄]
• A₃[NbS₄]
• A₃[TaS₄]
• A₂[MoSe₄]
• A₂[WS₄]
• A₂[WSe₄]
• A[ReS₄]
• MoS₄²⁻ (Bis-choline tetrathiomolybdate)

More complex tetrahedral anions include A₂[MoS_4-xO_x] and A₂[WS_4-xO_x]

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. Clinical studies have shown ATTM can effectively lower copper levels faster than currently available treatments, and that fewer patients with an initial neurological presentation of their disease who are treated with ATTM experience neurological deterioration

ATTM has also been found to have an inhibitory effect on angiogenesis, potentially via the inhibition of Cu ion dependent membrane translocation process involving a non-classical secretion pathway. This makes it an interesting investigatory treatment for cancer, age-related macular degeneration, and other diseases featuring excessive blood vessel deposition.