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Molybdenum(V) chloride

Molybdenum(V) chloride
Molybdenum(V) chloride
Ball-and-stick model of the Mo2Cl10 molecule in the crystal structure
IUPAC names
Molybdenum(V) chloride
Molybdenum pentachloride
ECHA InfoCard 100.030.510
EC Number 233-575-3
RTECS number QA4690000
Molar mass 273.21 g/mol (MoCl5)
Appearance dark-green solid
Density 2.928 g/cm3
Melting point 194 °C (381 °F; 467 K)
Boiling point 268 °C (514 °F; 541 K)
Solubility soluble in dry ether, dry alcohol, organic solvents
edge-shared bioctahedron
Main hazards oxidizer, hydrolyzes to release HCl
Flash point Non-flammable
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.[1]


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 dissociates to give a monomeric pentahalide.[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

MoCl5 is prepared by chlorination of Mo metal but also chlorination of MoO3. The unstable hexachloride MoCl6 is not produced in this way.[5]

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.[6] 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.[7]

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.[8]

Molybdenum hexachloride

Molybdenum(VI) chloride is known, but it cannot be prepared by addition of chlorine to MoCl5.[9]

Safety considerations

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


  1. ^ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego, CA: Academic Press. ISBN 0-12-352651-5.
  2. ^ Beck, J.; Wolf, F. (1997). "Three New Polymorphic Forms of Molybdenum Pentachloride". Acta Crystallogr. B53 (6): 895–903. doi:10.1107/S0108768197008331.
  3. ^ Wells, A. E. (1984). Structural Inorganic Chemistry (5th ed.). Oxford: Clarendon Press.
  4. ^ Brunvoll, J.; Ischenko, A. A.; Spiridonov, V. P.; Strand, T. G. (1984). "Composition and Molecular Structure of Gaseous Molybdenum Pentachloride by Electron Diffraction". Acta Chem. Scand. A38: 115–120. doi:10.3891/acta.chem.scand.38a-0115.
  5. ^ Tamadon, Farhad; Seppelt, Konrad (2013). "The Elusive Halides VCl5, MoCl6, and ReCl6". Angew. Chem. Int. Ed. 52 (2): 767–769. doi:10.1002/anie.201207552. PMID 23172658.
  6. ^ Dilworth, J. R.; Richards, R. L. (1990). "The Synthesis of Molybdenum and Tungsten Dinitrogen Compounds". Inorg. Synth. 28: 33–45. ISBN 0-471-52619-3.
  7. ^ Calderazzo, F.; Maichle-Mössmer, C.; Pampaloni, G.; Strähle, J. (1993). "Low-temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange". Dalton Trans. 1993 (5): 655–658. doi:10.1039/DT9930000655.
  8. ^ Kauffmann, T.; Torii, S.; Inokuchi, T. (2004). "Molybdenum(V) Chloride". Encyclopedia of Reagents for Organic Synthesis. New York, NY: J. Wiley & Sons. doi:10.1002/047084289 (inactive 2019-08-18).
  9. ^ Tamadon, Farhad; Seppelt, K. (2012). "The Elusive Halides VCl5, MoCl6, and ReCl6". Angewandte Chemie International Edition. 52: 767–769. doi:10.1002/anie.201207552.CS1 maint: Uses authors parameter (link)