Motion and Disorder in the Plastic Crystal of the C₇₀ Complex with Toluene by Solid State NMR and Thermal Analysis

Molecular motion and disorder in a C70 toluene complex of molar ratio 1/1 have been analyzed by obtaining 13C 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 C70 molecules start some orientational motion below 150 K. The well-known transitions of C70 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 C70 has a rotational correlation time of less than 100 μs, while for the toluene-containing C70 the motion is much less. The toluene molecules are closer to the equatorial “belt” of the C70 prolate spheroid and prohibit the C70 molecules from rotating isotropically.