Molybdenum(V) chloride

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.

Molybdenum(V) chloride

Partially oxidized MoCl5
Molybdenum(V) chloride
Names
IUPAC names Molybdenum(V) chloride Molybdenum pentachloride
Identifiers
CAS Number	10241-05-1 Y
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:30635
ChemSpider	55417
ECHA InfoCard	100.030.510
EC Number	233-575-3
PubChem CID	61497
RTECS number	QA4690000
UNII	BB0UFP2VO5 N
UN number	2508
CompTox Dashboard (EPA)	DTXSID0065012
InChI InChI=1S/5ClH.Mo/h5*1H;/q;;;;;+5/p-5 InChI=1S/10ClH.2Mo/h10*1H;;/q;;;;;;;;;;2*+4/p-8
SMILES Cl[Mo](Cl)(Cl)(Cl)Cl Cl1[Mo](Cl)(Cl)(Cl)(Cl)Cl[Mo]1(Cl)(Cl)(Cl)Cl
Properties
Chemical formula	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)
Solubility in water	hydrolyzes
Solubility	soluble in dry ether, dry alcohol, organic solvents
Structure
Crystal structure	monoclinic
Coordination geometry	edge-shared bioctahedron
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	oxidizer, hydrolyzes to release HCl
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P363, P405, P501
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). N verify (what is YN ?) Infobox references

Structure

Ball-and-stick model of the dimer in the crystal 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

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