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).

Additional recommended knowledge

Essential Laboratory Skills Guide

Daily Sensitivity Test

What is the Correct Way to Check Repeatability in Balances?

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:^[1]

[NH₄]₂[MoO₄] + 4 H₂S → [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).^[2] These organic salts are soluble in polar organic solvents such as acetonitrile and dmf.

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

Related compounds

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

• A₃[VS₄]^[4]
• A₃[NbS₄]^[4]
• A₃[TaS₄]^[4]
• A₂[MoSe₄]
• A₂[WS₄]^[5]
• A₂[WSe₄]
• A[ReS₄]^[6]

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

References

1. ^ Müller, A.; Diemann, E.; Jostes, R.; Bögge, H. (1981). "Transition Metal Thio Anions: Properties and Significance for Complex Chemistry and Bioinorganic Chemistry". Angewandte Chemie International Edition in English 20: 934. doi:10.1002/anie.198109341.
2. ^ Coucouvanis, D. (1998). "Syntheses, Structures, and Reactions of Binary and Tertiary Thiomolydate Complexes Containing the (O)Mo(S_x) and (S)Mo(S_x) Functional Groups (x = 1, 2, 4)". Advances in Inorganic Chemistry 45: 1-73.
3. ^ Alonso, G.; Berhault, G.; Aguilar, A.; Collins, V.; Ornelas, C.; Fuentes, S.; Chianelli, R. R. (2002). "Characterization and HDS Activity of Mesoporous MoS₂ Catalysts Prepared by in Situ Activation of Tetraalkylammonium Thiomolybdates". J. Catal. 208: 359-369. doi:10.1006/jcat.2002.3553.
4. ^ ^{a b c} Lee, S. C.; Li, J.; Mitchell, J. C.; Holm, R. H., (1992). "Group 5 Tetrathiometalates: Simplified Syntheses and Structures". Inorg. Chem. 31: 4333-4338. doi:10.1021/ic00047a021.
5. ^ Srinivasan, B. R.; Poisot, M.; Näther, C.; Bensch, W. (2004). "Diammonium tetrathiotungstate(VI), [NH₄]₂[WS₄], at 150 K". Acta Crystallographica Section E: Structure Reports Online E60: i136-i138.
6. ^ Goodman, J. T.; Rauchfuss, T. B., (2002). "Tetraethylammonium-tetrathioperrhenate [Et₄N][ReS₄]". Inorganic Syntheses 33: 107-110.