Nuclear magnetic resonance and differential thermal analysis studies of hydrogen molybdenum bronzes, H x MoO3

Sotani, Noriyuki; Eda, Kazuo; Kunitomo, M.

doi:10.1039/ft9908601583

Cited by 25 publications

(23 citation statements)

References 10 publications

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“…The highly broadened nature of the first endotherm at 100 °C is probably due to the presence of organic impurities as well. According to Sotani et al, hydrogen bronzes would yield exotherms (depending on the type of bronze) in the DSC profile at a temperature between 300 and 400 °C, due to the hydrogen elimination. The absence of exothermic response in the temperature region of 300−450 °C in the DSC profile eliminates the possibility of hydrogen bronze formation under sonochemical conditions.…”

Section: Resultsmentioning

confidence: 99%

Characterization of Sonochemically Prepared Unsupported and Silica-Supported Nanostructured Pentavalent Molybdenum Oxide

1997

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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.

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Section: Resultsmentioning

confidence: 99%

Characterization of Sonochemically Prepared Unsupported and Silica-Supported Nanostructured Pentavalent Molybdenum Oxide

1997

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“…[9][10][11]), but, despite the fact, the nature of this phenomenon has not established unequivocally up to date. According to various hypotheses, hydrogen could migrate in the form of a solvated proton [8,12], as a proton-electron pair [13,14], or as the atomic hydrogen [15,16]. The main difficulty in the explanation of SH phenomenon consists in that the SH concentration is too small to detect it by direct instrumental techniques using the modern spectroscopic methods, whereas the SH importance for the heterogeneous catalysis cannot be exaggerated.…”

Section: Solid Phase Isotope Exchange With Spillover Hydrogen In Aminmentioning

confidence: 99%

Solid phase isotope exchange with spillover hydrogen in amino acids, peptides, and proteins

2005

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We summarize here information on the theoretical and experimental study of high-temperature (150-200 degrees C) solid phase catalytic isotope exchange (HTSPCIE) carried out with amino acids, peptides, and proteins under the action of spillover hydrogen. Main specific features of the HTSPCIE reaction, its mechanism, and its use for studying spatial interactions in polypeptides are discussed. A virtually complete absence of racemization makes this reaction a valuable preparative method. The main regularities of the HTSPCIE reaction with the participation of spillover tritium have been revealed in the case of peptides and proteins, and the dependence of reactivity of peptide fragments on the spatial organization of their molecules has been studied. An important peculiarity of this reaction is that HTSPCIE proceeds at 150-200 degrees C with a high degree of chirality retention in amino acids and peptides. This is provided by its reaction mechanism, which consists in a synchronous one-center substitution at the saturated carbon atom characterized by the formation of pentacoordinated carbon and a three-center bond between the carbon and the incoming and outgoing hydrogen atoms.

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“…Similar arguments were used in subsequent modi"cations of Ritters approach by Bamberg and Schmitt (13,39), as well as in our own earlier work (7). Tanaka O from the bronze phases occurs only at higher temperatures for an inert atmosphere, while under mild conditions the deintercalation of hydrogen from the bronzes in the presence of oxygen and/or platinum (for the bronze samples produced by spillover) does not lead to oxygen de"cient oxides (37,41).…”

Section: Superstructure Determination Of Phase II (H Moo )mentioning

confidence: 99%

CDW Superstructures in Hydrogen Molybdenum Bronzes HxMoO3

Adams

2000

Journal of Solid State Chemistry

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Nuclear magnetic resonance and differential thermal analysis studies of hydrogen molybdenum bronzes, H x MoO3

Cited by 25 publications

References 10 publications

Characterization of Sonochemically Prepared Unsupported and Silica-Supported Nanostructured Pentavalent Molybdenum Oxide

Characterization of Sonochemically Prepared Unsupported and Silica-Supported Nanostructured Pentavalent Molybdenum Oxide

Solid phase isotope exchange with spillover hydrogen in amino acids, peptides, and proteins

CDW Superstructures in Hydrogen Molybdenum Bronzes HxMoO3

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