Molybdenum tetrachloride

Molybdenum tetrachloride is the inorganic compound with the empirical formula MoCl₄. The material exists as two polymorphs, a polymeric ("α") and a hexameric ("β") structures, although neither form is soluble in any solvent without degradation. In each polymorph, the Mo center is octahedral with two terminal chloride ligands and four doubly bridging ligands.

It can be prepared from by dechlorination of molybdenum pentachloride using tetrachloroethene:

2 MoCl₅ + C₂Cl₄ → 2 MoCl₄ + C₂Cl₆

The acetonitrile adduct, which is a versatile intermediate, can be prepared directly from the pentachloride:

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

The MeCN ligands can be exchanged with other ligands:

MoCl₄(CH₃CN)₂ + 2 THF → MoCl₄(THF)₂ + 2 CH₃CN