Molybdenum(V) chloride
Encyclopedia
Molybdenum chloride is the inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula [MoCl5]2. This dark volatile solid is an important starting reagent in the preparation of molybdenum compounds. In the solid state molybdenum pentachloride exists as a dimer with the formula Mo2Cl10, with a structure similar to that of the corresponding pentachlorides of W, Nb and Ta. In the gas phase, it is a monomeric pentahalide. It is paramagnetic, with one unpaired electron per Mo center, reflecting the fact that the formal oxidation state is 5+, leaving one valence electron.

Preparation and properties

MoCl5 is prepared by chlorination of Mo metal but also chlorination of MoO3. Notice that MoCl6 cannot be prepared under normal conditions. In contrast, the heavier analogues WCl6
Tungsten hexachloride
Tungsten hexachloride is the chemical compound of tungsten and chlorine with the formula WCl6. This dark violet blue species exists as a volatile solid under standard conditions. It is an important starting reagent in the preparation of tungsten compounds. WCl6 is a rare example of a...

 is well known.

MoCl5 is a strong oxidant, as indicated by its non-reactivity toward Cl2. It is easily reduced by even MeCN to afford the adduct MoCl4(MeCN)2, which in turn reacts with THF
ThF
Follicular B helper T cells , are antigen-experienced CD4+ T cells found in the B cell follicles of secondary lymphoid organs such as lymph nodes, spleens and Peyer's patches, and are identified by their constitutive expression of the B cell follicle homing receptor CXCR5...

 to give MoCl4(THF)2, a versatile reagent in the chemistry of molybdenum. MoCl5 is reduced by HBr to form MoBr4. The reaction is conducted in ethylbromide at -50 C:
2 MoCl5 + 10 HBr → 2 MoBr4 + 10 HCl + Br2

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

MoCl5 is a good Lewis acid toward non-oxidizable ligands. It forms an adduct with chloride to form [MoCl6]-. In organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

, the compound finds occasional use in chlorinations and deoxygenation reactions.

Safety considerations

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