C60•bromobenzene solvate:: Crystallographic and thermochemical studies and their relationship to C60 solubility in bromobenzene

Differential scanning calorimetry, solution calorimetry, and room-temperature single-crystal X-ray diffraction were used to study the thermodynamic and structural properties of a solvated crystal C-60. 2C(6)H(5)Br. In the monoclinic solvate, two orientations of C-60 were observed with fractional populations of 0.71 and 8.29. The enthalpy of solution of pure C-60 in bromobenzene was determined to be Delta(sol)H[C-60(s)] = -11.5 +/- -2.0 W/mol. The enthalpy of solution of the solvated crystal was Delta(sol)H[C-60. 2C(6)H(5)Br(s)] = +28 +/- 1 kJ/mol. The phase diagram of the system C-60-C6H5Br for T < 423 K was constructed. It predicts the existence of a maximum in the temperature-solubility relationship for C-60 in bromobenzene at 350 K. The activity of bromobenzene vapor over the solvated crystal is predicted to be reduced from its value over the pure liquid by a factor of 3.5.