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 orthohex agonal supercell of a hcp structure with symmetry Pbnm. It involves al ignment of the molecules with their long axis parallel to the original hexagonal axis, and a shift out of the original hcp positions. Interm olecular contacts are shown to be different from those found in C60. T he crystal is determined to contain stacking faults resulting in the p resence of AC and BC deformed hcp arrangements in addition to the orig inal AB stacking. The stacking disorder is shown to be independent of the phase transitions, and presumably is an intrinsic property of hexa gonal C70 crystals.