Structure and dynamics of octamethyl-ethinyl-ferrocene: an organometallic rotator phase Original Research Article

The onset of dynamics and the structural changes of octamethyl–ethinyl-ferrocene around a solid–solid phase transition at 248 K have been investigated using the novel technique of quasielastic nuclear forward scattering (QNFS) in a temperature range between 61 and 257 K at a photon energy of 14.413 keV, as well as X-ray powder diffraction at various energies. A pronounced hysteresis for both the dynamical and the structural properties is observed and confirmed by differential-scanning calorimetry. We assign the observed phenomena to a first-order transition from a low-symmetry low-temperature phase to a high-symmetry high-temperature plastically crystalline phase with nearly cubic symmetry. Possible mechanisms for this transition are discussed in the light of our results.