The low temperature heat capacities of fluorofullerenes

The heat capacities of the fluorinated fullerenes C60F48, C60F46, and C60F3 6 have been measured in an adiabatic vacuum calorimeter over the temperatur e range from 8 K to 356 K. The heat capacity curve of C60F48 reveals a grad ual "order-disorder" transition between the temperatures 315 K and 345 K. T hermodynamic properties of C60F48 in the transition region are as follows: T-trs = (329.6 +/- 0.4) K, Delta(trs)H = (7.0 +/- 0.7) kJ.mol(-1) and Delta (trs)S = (21 +/- 2) J.K(-1)mol(-1). The C-P curve of C60F46 exhibits a glas sy crystal transition in the temperature interval from 210 K to 245 K. The temperature dependence of the heat capacity of C60F36 does not indicate any anomaly. The molar thermodynamic functions H-m(o)(T) - H-m(o)(0), S-m(o)(T ) - S-m(o)(0), and G(m)(o)(T) - H-m(o)(0) over the temperature range studie d and entropies of formation Delta(f)(T) S-m(o) at T = 298.15 K have been c alculated for C60F48, C60F46, and C60F36. (C) 1999 Academic Press.