Molybdenum(V) chloride

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Molybdenum(V) chloride

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UN number	2508
Template:Longitem	Template:Chem2
Molar mass	273.21 g/mol (Template:Chem2)
Appearance	dark-green solid hygroscopic paramagnetic
Density	2.928 g/cm3
Melting point	Template:Chembox CalcTemperatures
Boiling point	Template:Chembox CalcTemperatures
Solubility	soluble in dry ether, dry alcohol, organic solvents
Template:Longitem	monoclinic
Template:Longitem	edge-shared bioctahedron
Flash point	Template:Chembox CalcTemperatures
Template:Longitem	Template:Ubl
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Molybdenum(V) chloride is the inorganic compound with the empirical formula Template:Chem2. This dark volatile solid is used in research to prepare other molybdenum compounds. It is moisture-sensitive and soluble in chlorinated solvents.

Structure

File:Molybdenum(V)-chloride-from-xtal-3D-balls.png

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 Template:Chem2. In the dimer, each molybdenum has local octahedral symmetry and two chlorides bridge between the molybdenum centers. A similar structure is also found for the pentachlorides of W, Nb and Ta. In the gas phase and partly in solution, the dimers partially dissociate to give a monomeric Template:Chem2. 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

Template:Chem2 is prepared by chlorination of Mo metal but also chlorination of Template:Chem2. The unstable hexachloride Template:Chem2 is not produced in this way.

Template:Chem2 is reduced by acetonitrile to afford an orange acetonitrile complex, Template:Chem2. This complex in turn reacts with THF to give Template:Chem2, a precursor to other molybdenum-containing complexes.

Molybdenum(IV) bromide is prepared by treatment of Template:Chem2 with hydrogen bromide:

Template:Chem2

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

Template:Chem2 is a good Lewis acid toward non-oxidizable ligands. It forms an adduct with chloride to form Template:Chem2. In organic synthesis, the compound finds occasional use in chlorinations, deoxygenation, and oxidative coupling reactions.

Reactions

Template:Chem2 is reduced by acetonitrile:

Template:Chem2

Although it polymerizes tetrahydrofuran, Template:Chem2 is stable in diethyl ether. Reduction of such solutions with tin gives Template:Chem2 and Template:Chem2, depending on conditions.

Safety considerations

Template:Chem2 is an aggressive oxidant and readily hydrolyzes to release HCl.

See also

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