C60 Solvate with (1,1,2)-Trichloroethane: Dynamic Statistical Disorder and Mixed Conformation

We present a full characterization of the orientationally disordered cocrystal of C60 with (1,1,2)-trichloroethane (C2H3Cl3), by means of X-ray diffraction, Raman spectroscopy, and broadband dielectric spectroscopy. Our results include the determination of molecular conformations, lattice structure, positional disorder, and molecular reorientational dynamics down to the microsecond time scale. We find that, while in the disordered solid phase of pure C2H3Cl3 the molecules exist only in the gauche conformation, both gauche and transoid conformers are present in the solvate, where they occupy the largest interstitial cavities between the fullerene species. The two C2H3Cl3 conformers exhibit separate, independent relaxations, exhibiting simply activated behavior in the measured temperature range. The relaxation of the transoid conformer, which has twice the dipole moment of the gauche isomer, is significantly slower than that of the latter, due to the high polarizability of C60 resulting in an electrostatic drag against the reorientations of the dipolar C2H3Cl3 species. The observation of two distinct, simply activated relaxations freezing at distinct temperatures indicates that they are not truly many-body relaxations, which may be rationalized considering that the C2H3Cl3 molecules are separated by the relatively bulky C60 spacers.