Ammonium tetrathiomolybdate is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula (NH₄)₂MoS₄. This bright red

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

salt is an important reagent in the chemistry of

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

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 oS₄sup>2− anion. The compound is prepared by treating solutions of

molybdate In chemistry a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Molybdenum can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, althou ...

, oO₄sup>2− with

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...

in the presence of ammonia: :(NH₄)₂MoO₄ + 4 H₂S → (NH₄)₂MoS₄ + 4 H₂O MoS4

Reactions

The anion is also an excellent ligand. For example, with Ni(II) sources, it forms i(MoS₄)₂sup>2−. Much of the chemistry of the thiomolybdate results from studies on salts of quaternised organic cations, such as Et₄sub>2 oS₄and Ph₄sub>2 oS₄(Et = C₂H₅, Ph = C₆H₅). These organic salts are soluble in polar organic solvents such as

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...

and dmf. The

thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...

of H₄sub>2 oS₄leads to molybdenum trisulfide (MoS₃), ammonia (NH₃) and hydrogen sulfide (H₂S), beginning at 155 °C till 280 °C. : (NH₄)₂MoS₄ → 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, Ph₄sup>+, Et₄sup>+) *A₃ S₄ *A₃ bS₄ref name=Lee1/> *A₃ aS₄ref name=Lee1/> *A₂ oSe₄*A₂ S₄ , *A₂ Se₄ ,

tetraethylammonium tetraselenotungstate Tetraethylammonium (TEA), () or (Et4N+) is a quaternary ammonium cation consisting of four ethyl groups attached to a central nitrogen atom, and is positively charged. It is a counterion used in the research laboratory to prepare lipophilic salts ...

*A eS₄*(C₅H₁₄NO)₂MoS₄ (

bis-choline tetrathiomolybdate Tiomolibdic acid (trade name Decuprate) is a chelating agent under investigation for the treatment of cancer and of Wilson's disease, a rare and potentially fatal disease in which the body cannot regulate copper. It is developed by Wilson Therap ...

) More complex tetrahedral anions include A₂ oS_4−xO_xand A₂ S_4−xO_x

Uses

Ammonium tetrathiomolybdate was first used therapeutically in the treatment of

copper toxicosis Wilson's disease is a genetic disorder in which excess copper builds up in the body. Symptoms are typically related to the brain and liver. Liver-related symptoms include vomiting, weakness, fluid build up in the abdomen, swelling of the legs, ...

in animals. It was then introduced as a treatment in

Wilson's disease Wilson's disease is a genetic disorder in which excess copper builds up in the body. Symptoms are typically related to the brain and liver. Liver-related symptoms include vomiting, weakness, fluid build up in the abdomen, swelling of the legs, ...

, 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 Various phase II clinical trial of ATTM for copper depletion in cancer have been performed. ATTM has also been found to have an inhibitory effect on

angiogenesis Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature by processes of sprouting and splitting ...

, 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 Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

age-related macular degeneration Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, som ...

, and other diseases featuring excessive blood vessel deposition.

References

{{DEFAULTSORT:Ammonium Tetrathiomolybdate Molybdates Sulfides Ammonium compounds Thiometallates