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 0.29. The enthalpy of solution of pure C 60 in bromobenzene was determined to be Δ sol H [C 60 (s)] = −11.5 ± 2.0 kJ/mol. The enthalpy of solution of the solvated crystal was Δ sol H [C 60 ·2C 6 H 5 Br(s)] = +28 ± 1 kJ/mol. The phase diagram of the system C 60 −C 6 H 5 Br 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.