Studies on the Hexagonal Hydrate of Molybdenum Trioxide. The Physical Properties of the Hydrate and Its Changes on Heat Treatments in Air, in Hydrogen, and in a Hydrogen–thiophene Mixture

Abstract The hexagonal hydrate (I) of molybdenum trioxide, which has been newly found and reported, was studied by X-ray diffraction analysis, IR and NMR spectroscopies, and by other methods. Also studied was the change in (I) on heat treatments in air, in hydrogen, and in a hydrogen–thiophene mixture. The crystal was found to belong to a hexagonal system. The air-dried sample has about 0.46 mol of water. This water is included as a water molecule, not as hydroxyl. By the dehydration of (I), anhydrous molybdenum trioxide (I′), which has the same crystal structure as (I), is obtained. Another new form of (I′) is the hexagonal trioxide, which is hygroscopic and which easily absorbs water when standing in air. This (I′) is metastable and is irreversibly transformed to rhombic molybdenum trioxide(II) at 420–430 °C. In hydrogen and in a hydrogen-thiophene mixture, reduction and sulfurization occur in addition to transformation, which can be shown schematically as: (Remark: Graphics omitted.). Transformation in hydrogen and in the hydrogen–thiophene mixture proceeds faster than in air. Reduction occurs more quickly in the hydrogen–thiophene mixture than in hydrogen.