Structural study and properties of the alkali metal, nitrosyl, and ammonium hepta- and octafluorouranates(VI)

Journal Article · Fri Oct 01 04:00:00 EDT 1976 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic50164a043· OSTI ID:7128234

Bougon, R; Charpin, P; Desmoulin, J P; Malm, J G

The thermal decomposition of the heptafluorouranates(VI) of the alkali metals is shown to take place in two steps. The first step gives the octafluorouranates(VI) and UF/sub 6/, and the decomposition rate is noticeable at temperatures above 100, 130, 150, and 210/sup 0/C for the Na, K, Rb, and Cs salts, respectively. The second step for Na/sub 2/UF/sub 8/ yields pure NaF and UF/sub 6/ above 300/sup 0/C, whereas the decomposition temperatures for the K, Rb, and Cs salts are above 300, 350, and 400/sup 0/C, respectively. Depending on the decomposition conditions, F/sub 2/ and M/sub 2/UF/sub 7/(M = K, Rb, Cs) or F/sub 2/, UF/sub 6/, and M/sub 3/UF/sub 8/ are formed. The heptafluorouranates(VI) of all the cations studied, except for ammonium, were shown to exhibit dimorphism. The parameters of their cubic form were obtained and are as follows: KUF/sub 7/; a = 5.22 A; RbUF/sub 7/; a = 5.385 A; CsUF/sub 7/; a = 5.517 A; NOUF/sub 7/; a = 5.334 A; NH/sub 4/UF/sub 7/; a = 5.393 A; NaUF/sub 7/(fccub), a = 8.511 A, Z = 4. The x-ray pattern of the low-symmetry form of CsUF/sub 7/ just below the solid transition temperature (15 +- 1/sup 0/C) was indexed with a tetragonal cell where a = 5.50 A and c = 5.37 A. The x-ray diagrams of the low symmetry form of the other MUF/sub 7/ salts were not indexed, whereas those of the octafluorouranates were indexed with orthorhombic cells. The vibrational spectra of the hepta- and octafluorouranates were found to be very dependent on the temperature, and for the same temperature on the cation size. Some trends observed in this study, like the thermal decomposition temperatures or the relative symmetries, are thought to arise from the differences in the cation--anion interaction. This interaction is stronger with smaller cations, which results in more distorted anions, less ionic U--F bonds, and paradoxically less stable complexes.

• Research Organization: CEN de Saclay, Gif-sur-Yvette, France
• OSTI ID: 7128234
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 15:10; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400104 -- Spectral Procedures-- (-1987)
400702* -- Radiochemistry & Nuclear Chemistry-- Properties of Radioactive Materials
ACTINIDE COMPOUNDS
ALKALI METAL COMPOUNDS
AMMONIUM COMPOUNDS
BOND LENGTHS
CESIUM COMPOUNDS
CHEMICAL PROPERTIES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COHERENT SCATTERING
DECOMPOSITION
DIFFRACTION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HIGH TEMPERATURE
INFRARED SPECTRA
KINETICS
MAGNETIC RESONANCE
MEDIUM TEMPERATURE
NITROSO COMPOUNDS
NUCLEAR MAGNETIC RESONANCE
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
POTASSIUM COMPOUNDS
PYROLYSIS
RAMAN SPECTRA
REACTION KINETICS
RESONANCE
RUBIDIUM COMPOUNDS
SCATTERING
SODIUM COMPOUNDS
SPECTRA
STRUCTURAL CHEMICAL ANALYSIS
SYNTHESIS
TEMPERATURE EFFECTS
URANIUM COMPOUNDS
URANIUM FLUORIDES
X-RAY DIFFRACTION