Molybdenum(V) chloride

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Molybdenum(V) chloride
Molybdenum(V) chloride
Names
IUPAC names
Molybdenum(V) chloride
Molybdenum pentachloride
Identifiers
10241-05-1 MoCl5
26814-39-1 Mo2Cl10
EC Number 233-575-3
PubChem 61497
RTECS number QA4690000
Properties
Cl10Mo2
Molar mass 273.21 g/mol
Appearance dark-green solid
hygroscopic
paramagnetic
Density 2.928 g/cm3
Melting point 194 °C (381 °F; 467 K)
Boiling point 268 °C (514 °F; 541 K)
hydrolyzes
Solubility soluble in dry ether, dry alcohol, organic solvents
Structure
monoclinic
edge-shared bioctahedron
Vapor pressure {{{value}}}
Related compounds
Other anions
 Molybdenum(V) fluoride
Molybdenum(IV) bromide
Molybdenum(III) iodide
Other cations
 Chromium(IV) chloride
Tungsten(V) chloride
Related molybdenum chlorides
 Molybdenum(II) chloride
Molybdenum(III) chloride
Molybdenum(IV) chloride
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

Molybdenum(V) chloride is the inorganic compound with the formula [MoCl5]2. This dark volatile solid is used in research to prepare other molybdenum compounds. it is moisture-sensitive and soluble in chlorinated solvents. Usually called molybdenum pentachloride, it is in fact a dimer with the formula Mo2Cl10.

Structure

Each molybdenum has local octahedral symmetry and two chlorides bridge between the molybdenum centers.[1] A similar structure is also found for the pentachlorides of W, Nb and Ta.[2] In the gas phase and partly in solution, the dimers partially dissociates to give a monomeric pentahalide.[3] 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

MoCl5 is prepared by chlorination of Mo metal but also chlorination of MoO3. MoCl6 is not produced, although the heavier analogue WCl6 is well known.[4]

MoCl5 is a strong oxidant. It is reduced by MeCN to afford an orange complex, MoCl4(MeCN)2, which in turn reacts with THF to give MoCl4(THF)2, a precursor to other molybdenum-containing complexes.[5] MoCl5 is reduced by HBr to form MoBr4. The bromination reaction is conducted in ethylbromide at -50 C, forming MoBr5 as an intermediate. Upon warming to 20 °C, Br2 is produced and the formal oxidation state of molybdenum changes from +5 to +4. The net transformation is shown in the equation:

2 MoCl5 + 10 HBr → 2 MoBr4 + 10 HCl + Br2

MoBr4 reacts with THF to give the Mo(III) species mer-MoBr3(THF)3.[6]

MoCl5 is a good Lewis acid toward non-oxidizable ligands. It forms an adduct with chloride to form [MoCl6]−. In organic synthesis, the compound finds occasional use in chlorinations, deoxygenation, and oxidative coupling reactions.[7]

Safety considerations

MoCl5 is an aggressive oxidant and readily hydrolyzes to release HCl.

References

  1. ↑ J. Beck and F. Wolf "Three New Polymorphic Forms of Molybdenum Pentachloride" Acta Cryst. 1997, vol. B53, pp.895-903.doi:10.1107/S0108768197008331
  2. ↑ Wells, A. E (1984). Structural Inorganic Chemistry, 5th ed. Oxford: Clarendon Press.
  3. ↑ Brunvoll, J., Ischenko, A. A., Spiridonov, V. P. & Strand, T. G. Acta Chem. Scand. 1984, volume A38, pp. 115-120.
  4. ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  5. ↑ Dilworth, J. R.; Richards, R. L. "The Synthesis of Molybdenum and Tungsten Dinitrogen Compounds" Inorganic Syntheses, 1990, volume 28, pages 33-45. ISBN 0-471-52619-3.
  6. ↑ Calderazzo, F.; Maichle-Mössmer, C.; Pampaloni, G.; Strähle, J. "Low-temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange", Journal of the Chemical Society, Dalton Transactions, 1993, pages 655-8.doi:10.1039/DT9930000655
  7. ↑ T. Kauffmann, S. Torii, T. Inokuchi “Molybdenum(V) Chloride” in Encyclopedia of Reagents for Organic Synthesis 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
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