LOW-TEMPERATURE STRUCTURE OF SOLID C-70

The structure of the low-temperature phase of hexagonal close-packed (hcp) grown C70 is determined from single-crystal X-ray diffraction at 220 K and 100 K. An ordering of the molecules is found on the orthohexagonal supercell of a hcp structure with symmetry Pbnm. It involves alignment of the molecules with their long axis parallel to the original hexagonal axis, and a shift out of the original hcp positions. Intermolecular contacts are shown to be different from those found in C60. The crystal is determined to contain stacking faults resulting in the presence of AC and BC deformed hcp arrangements in addition to the original AB stacking. The stacking disorder is shown to be independent of the phase transitions, and presumably is an intrinsic property of hexagonal C70 crystals.