Molybdenum tetrachloride

Molybdenum tetrachloride is the inorganic compound with the empirical formula MoCl4. The material exists as two polymorphs, both being dark-colored paramagnetic solids. These compounds are mainly of interest as precursors to other molybdenum complexes.

Structure

The α polymorph is a polymer. The β polymorph is a hexamer. In both polymorph, the Mo center is octahedral with two terminal chloride ligands and four doubly bridging ligands. In addition to these two binary phases, a number of adducts are known with the formula MoCl4L2 where L is a Lewis base.

Preparation

α-Molybdenum tetrachloride can be prepared from by dechlorination of molybdenum pentachloride using tetrachloroethene:

2 MoCl5 + C2Cl4 → 2 MoCl4 + C2Cl6

Heating α-molybdenum tetrachloride in a sealed container in the presence of molybdenum pentachloride induces conversion to the β polymorph.

Reactions

When heated in an open container, molybdenum tetrachloride evolves chlorine, giving molybdenum trichloride;

2 MoCl4 → 2 MoCl3 + Cl2

The acetonitrile complex adduct can be prepared by reduction of the pentachloride with acetonitrile:

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

The pentachloride can be reduced to the ether complex MoCl4(Et2O)2 using tin powder. It is a beige, paramagnetic solid.