Molybdenum(V) chloride
Molybdenum(V) chloride
Ball-and-stick model of the Mo2Cl10 molecule in the crystal structure

Partially oxidized MoCl5
Names
IUPAC names
Molybdenum(V) chloride
Molybdenum pentachloride
Identifiers
3D model (JSmol)
ECHA InfoCard 100.030.510
EC Number
  • 233-575-3
RTECS number
  • QA4690000
UNII
  • InChI=1S/5ClH.Mo/h5*1H;/q;;;;;+5/p-5
  • InChI=1S/10ClH.2Mo/h10*1H;;/q;;;;;;;;;;2*+4/p-8
  • Cl[Mo](Cl)(Cl)(Cl)Cl
  • Cl1[Mo](Cl)(Cl)(Cl)(Cl)Cl[Mo]1(Cl)(Cl)(Cl)Cl
Properties
Mo2Cl10
Molar mass 273.21 g/mol (MoCl5)
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
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 oxidizer, hydrolyzes to release HCl
Flash point Non-flammable
Related compounds
Other anions
Other cations
Related molybdenum chlorides
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 empirical formula MoCl5. 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 Mo2Cl10.[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 MoCl5.[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 reduced by acetonitrile to afford an orange acetonitrile complex, MoCl4(CH3CN)2. This complex in turn reacts with THF to give MoCl4(THF)2, a precursor to other molybdenum-containing complexes.[6]

Molybdenum(IV) bromide is prepared by treatment of MoCl5 with hydrogen bromide:

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

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

Reactions

MoCl5 is reduced by acetonitrile:[9]

2 MoCl5 + 5 CH3CN → 2 MoCl4(CH3CN)2 + HCl + ClCH2CN

Although it polymerizes tetrahydrofuran, MoCl5 is stable in diethyl ether. Reduction of such solutions with tin gives MoCl4((CH3CH2)2O)2 and MoCl3((CH3CH2)2O)3, depending on conditions.[10]

Safety considerations

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

See also

References

  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. S2CID 95489209.
  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, Jonathan R.; Richards, Raymond L. (1990). "The Synthesis of Molybdenum and Tungsten Dinitrogen Complexes". Inorganic Syntheses. Inorganic Syntheses. Vol. 28. pp. 33–43. doi:10.1002/9780470132593.ch7. ISBN 9780470132593.
  7. ↑ Calderazzo, Fausto; Maichle-Mössmer, Cäcilie; Pampaloni, Guido; Strähle, Joachim (1993). "Low-Temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange". J. Chem. Soc., Dalton Trans. (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:10.1002/047084289X. hdl:10261/236866. ISBN 9780471936237.
  9. ↑ Dilworth, Jonathan R.; Richards, Raymond L. (1990). The Synthesis of Molybdenum and Tungsten Dinitrogen Complexes. Inorganic Syntheses. Vol. 28. pp. 33–43. doi:10.1002/9780470132593.ch7. ISBN 9780470132593.
  10. ↑ Maria, Sébastien; Poli, Rinaldo (2014). "Ether Complexes of Molybdenum(III) and Molybdenum(IV) chlorides". Inorganic Syntheses: Volume 36 (PDF). Inorganic Syntheses. Vol. 36. pp. 15–18. doi:10.1002/9781118744994.ch03. ISBN 9781118744994.
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