Rhenium oxide, /3-, single

Rhenium oxide supported on alumina is present on the surface as a single rhenium species. Laser-Raman spectroscopy studies by Kerkhof, MouUjn, and Thomas indicate that the species consists of tetrahedral Re04 ions, which are dynamically distorted by the carrier or surface hydroxyl groups, as illustrated by the broadening of the band at 916 cm". Neither laser-Raman spectroscopy nor X-ray diffraction indicates that other rhenium species, e.g., octahedrally co-ordinated rhenium or Al-Re-0 compounds, are formed. 

Carburization of rhenium filaments has been used to optimize Th and Pa ionization efficiency for TIMS analysis on single filaments (Esat 1995). ReC has a greater work function than Re metal, and elemental oxidation state is maintained in the reduced or metal state by the presence of carbon in the filament. Using this method and a mass spectrometer with improved ion optics, Esat (1995) was able to improve Th transmission and ionization efficiency by about a factor of 30 over conventional methods. Using more conventional mass spectrometry, Murrell et al. (personal communication) were able to improve ionization efficiency for Pa and Th by a factor of 5-10 over conventional graphite sandwich loads on Re filaments (Goldstein et al. 1989 Pickett et al. 1994). For Pa analysis, one drawback is that Pa and U ionization commonly overlap using this... 

The crystal structure of cadmium rhenium(V) oxide, as determined by single-crystal technique,1 is of the face-centered cubic pyrochlore type (a = 10.219 A.). The only positional parameter for the 48 (/) oxygens is x = 0.309 0.007 when rhenium is at the origin. The density, determined pycnometrically, is 8.82 0.03 g./cc., compared with the theoretical value of 8.83 g./cc. for Z = 8. The resistivity between 4.2 K and room temperature is very low (10-3-10-4 J2-cm.) and has a positive temperature coefficient. Over the same temperature range the magnetic susceptibility is low and temperature-independent. These properties indicate that cadmium rhenium(V) oxide exhibits metallic conductivity. 

The observed E0 values in this case indicate the highest stability of rhenium (V) derivatives in this series. The comparison of the preparative data published indicates that these are the +5 and +6 oxidation states that appear to be most stable for the alkoxocomplexes of rhenium. The low-valent (+1 — +3) complexes should either be stabilized by JT-acceptor ligands (CO, PR3, NO, unsaturated hydrocarbons) or contain multiple M M bonds [321, 586, 729, 762,]. The compounds of rhenium (VII) are very unstable and decompose at room temperature in several minutes when isolated. They can be isolated and kept for several days as the complexes with N-donor ligands such as Tmeda or Py [533, 519, 1358]. The decomposition products of rhenium (VI) and (VIT) alkoxides are often described in literature as a black tar. The compound with this kind of appearence turned to be the major product of the anodic oxidation of rhenium in methanol (at high current density) and was shown by the X-ray single crystal study to be Re402(0Me)16 [906]. 

Primary bis-homoallylic alcohols have been found to react with rhenium(VII) oxide (Re207) leading to 2-hydroxyalkyl tetrahydrofurans as single isomers140 l42. 

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