Identification of a rotator phase of octamethyl ferrocene and correlations 
between its structural and dynamical properties

Asthalter, T.; Sergueev, I.; van Bürck, U.; Dinnebier, R. E.

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Identification of a rotator phase of octamethyl ferrocene and correlations between its structural and dynamical properties

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Dinnebier, R. E.
Scientific Facility X-Ray Diffraction (Robert E. Dinnebier), Max Planck Institute for Solid State Research, Max Planck Society;

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Citation

Asthalter, T., Sergueev, I., van Bürck, U., & Dinnebier, R. E. (2006). Identification of a rotator phase of octamethyl ferrocene and correlations between its structural and dynamical properties. Journal of Physics and Chemistry of Solids, 67(7), 1416-1422.

Cite as: https://hdl.handle.net/21.11116/0000-000E-FC5C-0

Abstract

The low- and high-temperature phases of octamethyl ferrocene were
studied in detail, using high-resolution X-ray powder diffraction,
differential scanning calorimetry and nuclear resonant scattering, in
particular the novel technique of synchrotron radiation perturbed
angular correlations (SRPAC). Much as in the case of an analogous but
more unsymmetrical molecule, octamethyl ethinyl ferrocene, the
high-temperature phase possesses the space group R3m with lattice
parameters a = b = 12.5568(1) angstrom, c = 9.6045(1) angstrom, which
in the rhombohedral setting correspond to a = 7.9251(1) angstrom, alpha
= 104.79 degrees. An increase of the volume per formula unit of about
12% across the phase transition is observed.
The rotation of the electric field gradient, which can be identified
with the rotation of the entire molecule within the lattice, follows
Arrhenius behaviour with a high activation energy of (40.3 +/- 3.3) kJ
mol(-1). Whereas precursor effects and a change in activation energy
were observed for octamethyl ethinyl ferrocene, no such effects are
observed for octamethyl ferrocene. We relate this difference to the
absence of the ethinyl substituent in octamethyl ferrocene. (c) 2006
Elsevier Ltd. All rights reserved.