We describe the preparation and characterization of unusual pentavalent molybdenum oxide stabilized by water molecules, Mo2O5·2H2O. Ultrasound irradiation of a slurry of molybdenum hexacarbonyl, Mo(CO)6, in Decalin for 3 h under ambient air yields blue-colored Mo2O5·2H2O. Infrared (FT-IR) spectrum analysis of the resulting blue product reveals that the Mo ions possess molybdenyl bonds (MoO) and Mo−O character and also shows the presence of hydrogen-bonded, as well as coordinated, water molecules. The DSC profile of the blue oxide shows the presence of two endothermic peaks at around 100 °C and 140 °C, corresponding to the elimination of hydrogen-bonded and coordinated water molecules, respectively. The amount of water molecules was determined by thermogravimetric analysis (TGA). Characterization using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) with selected area electron diffraction (SAED) shows the amorphous nature of the blue product. The TEM picture shows that the blue oxide is composed of spongy platelet nanoparticles (∼20 nm). Heating the initial blue powder at 300 °C for 2 days under an oxygen, hydrogen, and nitrogen atmosphere yields X-ray crystalline MoO3, MoO2, and a mixture of MoO3 and MoO2, respectively. X-ray photoelectron spectroscopy (XPS), along with the potentiometric titration analysis of the blue oxide, confirms the formation of pentavalent molybdenum oxide. UV−visible absorption studies of the blue product demonstrate that the characteristic absorption of the Mo(V) (d-cation) oxide system and the Mo ions probably consists of two types of coordination symmetry (T d and O h ). Electron spin resonance (ESR) experimental results revealed an unusual doublet pattern, which is ascribed to superhyperfine coupling of pentavalent molybdenum with a proton of coordinated water. The nanostructured amorphous pentavalent molybdenum oxide (blue oxide) thus formed has also been successfully deposited on Stober's silica micropheres (250 nm) ultrasonically. The TEM images of silica-supported blue oxide reveal uniform distribution and strong adhering nature of the blue oxide. FT-IR spectroscopy illustrated the structural changes that occur when the amorphous SiO2 is coated sonochemically with the blue oxide.

A novel sonochemical approach for the preparation of molybdenum oxide (Mo 2 O 5 ‚xH 2 O) and molybdenum carbide (Mo 2 C) clusters coated on silica carriers, in which Mo(CO) 6 precursor serves as an in situ source for the coating phase of both materials (molybdenum oxide and molybdenum carbide), has been described. Ultrasonic irradiation of a slurry of molybdenum hexacarbonyl, Mo(CO) 6 , and silica microspheres in decane for 3 h, under ambient air and argon, yields diphasic molybdenum oxide-silica (MOS) and molybdenum carbide-silica (MCS) composites, respectively. Characterization using powder X-ray diffraction and transmission electron microscopy, with selected area electron diffraction, shows the amorphous nature of the nanocomposites. The phase evolution by long-term thermal reduction of MOS under H 2 shows that the Mo 2 O 5 undergoes stepwise reduction following the sequence, Mo V f Mo IV f Mo o . The TEM image of MOS and MCS shows that the sonochemical decomposition products of Mo(CO) 6 attached on the silica carrier as clusters, as thin layers, or as nanoparticles depends upon the precursor composition. UV-visible absorption studies on the sonochemically produced MOS demonstrate that the characteristic absorption of the Mo V (d 1 cation) oxide system and the Mo ions are likely to possess two types of coordination symmetry (T d and O h ). Considerable changes in the characteristic UV-visible absorption of MOS, compared to that of bulk molybdenum oxide and bare silica, was observed, perhaps associated with the chemical interaction, to form a desirable interfacial bond. FT-IR spectroscopy illustrated the structural changes that occur when the amorphous SiO 2 is coated sonochemically. It has been proposed that the coating takes place via ultrasonic-cavitation-induced decomposition of the precursor into the required coating phase and the breaking of the strained siloxane link of the silica; subsequently, the coating phase and silica particles collide with each other and deposit themselves into the coating.