Solid-State Studies on a C₆₀ Solvate Grown from 1,1,2-Trichloroethane

Abstract

Single and 10-fold-twinned crystals of the C 60 1:1 solvate formed with 1,1,2-trichloroethane were examined by means of scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry and thermogravimetry. Solubility of C 60 in 1,1,2-trichloroethane was found to be 130 ± 10 mg per liter of solution in equilibrium with solvate crystals at 296 ± 2 K. The lattice metrics of the solvate is orthorhombic ( a = 10.164(3) Å, b = 31.390(6) Å, c = 10.130(4) Å, β = 90.00(2)°), with axis c as a twin axis, although the symmetry is monoclinic (space group P 2 1 / n ). The solvate forms with a negative excess volume (−58 Å 3 per formula unit), and its packing coefficient (0.76) is higher than that for close packing of hard spheres. On heating, desolvation into cubic C 60 and TCAN vapor occurs in one step at 436 K (onset) with a related enthalpy, +48 kJ per mole of solvate, close to the sublimation enthalpy for pure solvent. On aging at room temperature in the dark, no degradation of big (≈1 × 10− 3 mm 3 ) solvate crystals into fcc C 60 is observed after 4 years have elapsed.