Issue 16, 2016

Structure and reorientational dynamics of 1-F-adamantane

Abstract

The polymorphism and the dynamics of a simple rigid molecule (1-fluoro-adamantane) have been studied by means of X-ray powder diffraction and broadband dielectric spectroscopy. At temperatures below the melting point, the molecule forms an orientationally disordered Phase I with a cubic-centered structure (Phase I, Fm[3 with combining macron]m, Z = 4). This phase possesses eight equilibrium positions for the fluorine atom, with equal occupancy factors of 1/8. A solid–solid phase transition to a low-temperature tetragonal phase (Phase II, P[4 with combining macron]21c, Z = 2) reduces the statistical disorder to only four possible equivalent sites for the fluorine atom, with fractional occupancies of 1/4. The dynamics has been rationalized under the constraints imposed by the space group of the crystal structure determined by powder X-ray diffraction. The dielectric spectroscopy study reveals that the statistical disorder in Phase II is dynamic in character and is associated with reorientational jumps along the two- and three-fold axes. In the dielectric loss spectra, the cooperative (α) relaxation exhibits a shoulder on the high-frequency side. This remarkable finding clearly reveals the existence of two intrinsic reorientational processes associated with the exchange of the F atom along the four sites. In addition to such “bimodal” relaxation, a secondary Johari–Goldstein relaxation is detected at lower temperatures.

Graphical abstract: Structure and reorientational dynamics of 1-F-adamantane

Supplementary files

Article information

Article type
Paper
Submitted
19 Feb 2016
Accepted
17 Mar 2016
First published
17 Mar 2016

Phys. Chem. Chem. Phys., 2016,18, 10924-10930

Structure and reorientational dynamics of 1-F-adamantane

B. Ben Hassine, Ph. Negrier, M. Romanini, M. Barrio, R. Macovez, A. Kallel, D. Mondieig and J. Ll. Tamarit, Phys. Chem. Chem. Phys., 2016, 18, 10924 DOI: 10.1039/C6CP01144F

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