MOTION AND DISORDER IN THE PLASTIC CRYSTAL OF THE C-70 COMPLEX WITH TOLUENE BY SOLID-STATE NMR AND THERMAL-ANALYSIS

Molecular motion and disorder in a C-70 toluene complex of molar ratio 1/1 have been analyzed by obtaining C-13 NMR powder patterns and magic angle spinning spectra over the temperature range from 150 to 373 K, as well as by DSC measurement of heat capacity and heats of transition from 120 to 560 K. The C-70 molecules start some orientational motion below 150 K. The well-known transitions of C-70 between 260 and 350 K are suppressed in the complex, but the toluene molecules contribute a liquid-like heat capacity above 178 K. Evaporation of the toluene occurs sharply at 446 K with a heat of decomposition of 36.1 kJ/mol (2.9 kJ/mol more than the heat of evaporation of pure toluene and 62 K higher than the boiling temperature of toluene). At room temperature and above, pure C-70 has a rotational correlation time of less than 100 mu s, while for the toluene-containing C-70 the motion is much less. The toluene molecules are closer to the equatorial ''belt'' of the C-70 prolate spheroid and prohibit the C-70 molecules from rotating isotropically.