C-60-CENTER-DOT-BROMOBENZENE SOLVATE - CRYSTALLOGRAPHIC AND THERMOCHEMICAL STUDIES AND THEIR RELATIONSHIP TO C-60 SOLUBILITY IN BROMOBENZENE

Differential scanning calorimetry, solution calorimetry, and room-temp erature single-crystal X-ray diffraction were used to study the thermo dynamic 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 solutio n 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 cr ystal was Delta(sol)H[C-60. 2C(6)H(5)Br(s)] = +28 +/- 1 kJ/mol. The ph ase diagram of the system C-60-C6H5Br for T < 423 K was constructed. I t predicts the existence of a maximum in the temperature-solubility re lationship for C-60 in bromobenzene at 350 K. The activity of bromoben zene vapor over the solvated crystal is predicted to be reduced from i ts value over the pure liquid by a factor of 3.5.