Molybdenum Oxychlorides

Several Molybdenum Oxychlorides have been described. The compounds Mo₂O₃Cl₂ and Mo₃O₃Cl₇ have been stated to be formed by the reduction of the oxychloride MoOCl₄.

The compound Mo₂O₃Cl₅ was stated by Blomstrand to be formed as reddish-brown, fusible crystals by condensation of the brown vapours which are produced when chlorine is passed over heated molybdenum sesquioxide, Mo₂O₃.

The oxychloride MoO₂Cl₂ is obtained when chlorides of molybdenum are heated in the air, and, among other compounds, when the dioxide, or a mixture of the trioxide with carbon, is heated in chlorine, or when molybdenum trioxide and phosphorus trichloride are heated together; it is not formed, however, when a mixture of common salt, sulphuric acid, and molybdenum trioxide is heated. A pale yellow amorphous substance, soluble in water and alcohol, it is easily sublimed, and is reduced on heating in hydrogen or carbon monoxide to the dioxide.

The compound Mo₃O₅Cl₈ is stated to be a stable red crystalline substance which is produced on heating the compound Mo₂O₃Cl₆; the latter is a violet crystalline deliquescent body, soluble in water, produced by reduction in hydrogen of the oxychloride MoOCl₄. It sublimes on heating; when heated in the air it is oxidised to the oxychloride MoO₂Cl₂ and chlorine; its aqueous solution is unstable.

The oxychloride MoOCl₄ is formed on heating in chlorine a mixture of molybdenum pentachloride and the compound MoO₂Cl₂:

2MoCl₅ + 2MoO₂Cl₂ + Cl₂ = 4MoOCl₄;

or by using instead appropriate quantities of the metal and the dioxide. The substance is considered by Nordenskjold to be a mixture in varying proportions of the pentachloride with the oxychloride MoO₂Cl₂. The crystals obtained, on purification by sublimation, have a dark green colour and metallic lustre. They readily fuse and vaporise, and are affected by sunlight. The aqueous solution is unstable; on heating alone, the compound Mo₂O₃Cl₆ is formed; while in hydrogen it gives the oxychlorides Mo₃O₃Cl₇ and MoO₂Cl₂, molybdenum dichloride and molybdenum.

The following compounds have also been prepared: MoOCl₃.2NH₄Cl, MoOCl₃.2KCl.2H₂O, MoOCl₃.2RbCl, MoOCl₃.2CsCl, together with similar compounds with certain organic bases.