Abstract: | Synchrotron radiation was used to measure the EXAFS and XANES polarization dependences for intercalation compounds of graphite
fluoride. An approach is developed which allows one to analyze the orientation of molecules of arbitrary shapes using XANES
and EXAFS data. Analyzing the orientation dependences of BrK XANES spectra for the T-shaped BrF3 molecules, we determined possible combinations and admissible ranges of angles between the normal to the graphite fluoride
matrix planes and the Br−F bond directions (α=52–90°, β=27–82°) and between the normal to the matrix planes and the molecular
planes (γ=27–53°). The average orientation angles obtained by the combined analysis of the EXAFS and XANES data are as follows:
α=62±1.5°, β=58±1.5°, γ=45±1.5°. The interatomic distances Br−F, Br−Br, and Fe−Br are determined. It is established that thermal
treatment, which recovers the X-ray diffraction pattern from the unfilled matrix, does not affect the predominant orientation
of the BrF3 molecules. This suggests that the thermally treated graphite fluoride matrix contains thin layers of ordered molecules. The
absence of the polarization dependence of the spectra of FeBr3 in graphite fluoride allows the assumption that the molecular planes are oriented with respect to the normal to the matrix
planes at a “magic” angle of 35°.
Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 6, pp. 1020–1029, November–December, 1995.
Translated by I. Izvekova |