SOLID-STATE STUDIES ON SINGLE AND DECAGONAL CRYSTALS OF C-60 GROWN FROM 1,2-DICHLOROETHANE

By slowly evaporating solutions of fullerene C-60 in 1,2-dichloroethan e at room temperature, crystals of an orthorhombic 1:1 solvate are obt ained [Cmcm, Cmc2(1), or Ama2, with a=10.065(9) Angstrom, b=31.34(3) A ngstrom, and c=10.059(8) Angstrom (C setting)]. Unusual decagonal need les with dihedral angles of similar to 36 degrees between adjacent fac es also form. They are described in terms of a 10X twinning of these o rthorhombic crystals with needle axis (or twin axis [001]) parallel to composition planes in the form {1K0} whose orientations do not corres pond to rational index k (9 < K < 10). This solvate decomposes with a desolvation enthalpy (45 kJ per mole of solvent) close to that of subl imation for pure solvent and it forms with a negative excess Volume (- 23 Angstrom(3) per formula unit). Despite a packing coefficient (0.77) higher than that for hard sphere close packing (0.74), it spontaneous ly decomposes at room temperature. This is related to the solvent adso rption on cubic C-60 which is shown to be preferred to the solvate for mation by about -10 kJ per mole of solvent. [S0163-1829(98)03117-8].