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.
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.[1] In addition to these two binary phases, a number of adducts are know with the formula where L is a Lewis base.
α-Molybdenum tetrachloride can be prepared from by dechlorination of molybdenum pentachloride using tetrachloroethene:[2]
2MoCl5 + C2Cl4 → 2MoCl4 + C2Cl6
Heating α-molybdenum tetrachloride in a sealed container in the presence of molybdenum pentachloride induces conversion to the β polymorph.[2]
When heated in an open container, molybdenum tetrachloride evolves chlorine, giving molybdenum trichloride;[2]
2MoCl4 → 2MoCl3 + Cl2
The acetonitrile complex adduct can be prepared by reduction of the pentachloride with acetonitrile:[3] [4]
2MoCl5 + 5CH3CN → 2MoCl4(CH3CN)2 + ClCH2CN + HClThe MeCN ligands can be exchanged with other ligands:
MoCl4(CH3CN)2 + 2THF → MoCl4(THF)2 + 2CH3CN
The pentachloride can be reduced to the ether complex MoCl4(Et2O)2 using tin powder. It is a beige, paramagnetic solid.[5]