Molybdenum(V) chloride explained

Molybdenum(V) chloride is the inorganic compound with the empirical formula . This dark volatile solid is used in research to prepare other molybdenum compounds. It is moisture-sensitive and soluble in chlorinated solvents.

Structure

Usually called molybdenum pentachloride, it is in fact partly a dimer with the molecular formula .^[1] In the dimer, each molybdenum has local octahedral symmetry and two chlorides bridge between the molybdenum centers.^[2] A similar structure is also found for the pentachlorides of W, Nb and Ta.^[3] In the gas phase and partly in solution, the dimers partially dissociate to give a monomeric .^[4] The monomer is paramagnetic, with one unpaired electron per Mo center, reflecting the fact that the formal oxidation state is +5, leaving one valence electron on the metal center.

Preparation and properties

is prepared by chlorination of Mo metal but also chlorination of . The unstable hexachloride is not produced in this way.^[5]

is reduced by acetonitrile to afford an orange acetonitrile complex, . This complex in turn reacts with THF to give, a precursor to other molybdenum-containing complexes.^[6]

Molybdenum(IV) bromide is prepared by treatment of with hydrogen bromide:

The reaction proceeds via the unstable molybdenum(V) bromide, which releases bromine at room temperature.^[7]

is a good Lewis acid toward non-oxidizable ligands. It forms an adduct with chloride to form . In organic synthesis, the compound finds occasional use in chlorinations, deoxygenation, and oxidative coupling reactions.^[8]

Reactions

is reduced by acetonitrile:^[9]

Although it polymerizes tetrahydrofuran, is stable in diethyl ether. Reduction of such solutions with tin gives and, depending on conditions.^[10]

Safety considerations

is an aggressive oxidant and readily hydrolyzes to release HCl.

See also

• Molybdenum(IV) chloride
• Molybdenum(VI) chloride
• Molybdenum(V) fluoride
• Tungsten(V) chloride

References

1. Book: Holleman . A. F.. Wiberg. E. . Inorganic Chemistry . Academic Press. San Diego, CA. 2001 . 0-12-352651-5.
2. J. . Beck . F. . Wolf . Three New Polymorphic Forms of Molybdenum Pentachloride. Acta Crystallogr. . 1997 . B53 . 6 . 895–903. 10.1107/S0108768197008331. 95489209 .
3. Book: Wells, A. E. . 1984 . Structural Inorganic Chemistry . 5th . Oxford . Clarendon Press.
4. Brunvoll . J. . Ischenko . A. A. . Spiridonov . V. P. . Strand . T. G. . Composition and Molecular Structure of Gaseous Molybdenum Pentachloride by Electron Diffraction. Acta Chem. Scand. . 1984 . A38 . 115–120. 10.3891/acta.chem.scand.38a-0115. free .
5. Farhad . Tamadon . Konrad . Seppelt . The Elusive Halides VCl₅, MoCl₆, and ReCl₆ . . 2013 . 52 . 2 . 767–769 . 10.1002/anie.201207552 . 23172658 .
6. Book: Inorganic Syntheses . 28 . The Synthesis of Molybdenum and Tungsten Dinitrogen Complexes . 1990 . 10.1002/9780470132593.ch7. Dilworth . Jonathan R. . Richards . Raymond L. . Inorganic Syntheses . 33–43 . 9780470132593 .
7. 10.1039/DT9930000655. Low-Temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange. J. Chem. Soc., Dalton Trans.. 5. 655–658. 1993. Calderazzo. Fausto. Maichle-Mössmer. Cäcilie. Pampaloni. Guido. Strähle. Joachim.
8. Encyclopedia: T.. Kauffmann. S.. Torii. T.. Inokuchi . Molybdenum(V) Chloride . Encyclopedia of Reagents for Organic Synthesis . 2004 . J. Wiley & Sons . New York, NY. 10.1002/047084289X. 9780471936237. 10261/236866. free.
9. Book: 28 . The Synthesis of Molybdenum and Tungsten Dinitrogen Complexes . 1990 . 10.1002/9780470132593.ch7. Dilworth . Jonathan R. . Richards . Raymond L. . Inorganic Syntheses . 33–43. 9780470132593 .
10. Book: 10.1002/9781118744994.ch03. Ether Complexes of Molybdenum(III) and Molybdenum(IV) chlorides . Inorganic Syntheses. 36 . 2014 . Maria . Sébastien . Poli . Rinaldo . Inorganic Syntheses: Volume 36 . 15–18. 9781118744994 .