Molybdenum tetrachloride
# Molybdenum tetrachloride

Molybdenum tetrachloride is the inorganic compound with the empirical formula $MoCl_4.$ 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 know with the formula $MoCl_4L_2$ where L is a Lewis base.

## Preparation

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

    2 $MoCl_5$ + $C_2Cl_4$ → 2 $MoCl_4$ + $C_2Cl_6$

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 $MoCl_4$ → 2 $MoCl_3$ + $Cl_2$

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

    2 $MoCl_5$ + 5 $CH_3CN$ → 2 $MoCl_4(CH_3CN)_2$ + $ClCH_2CN$ + HCl

The MeCN ligands can be exchanged with other ligands:

    $MoCl_4(CH_3CN)_2$ + 2 THF → $MoCl_4(THF)_2$ + 2 $CH_3CN$

The pentachloride can be reduced to the ether complex $MoCl_4(Et_2O)_2$ using tin powder. It is a beige, paramagnetic solid.

