The vapor pressures of C-76 were measured over the temperature range 834-1069 K by the torsion-effusion method. The results are well represented by the following linear equation : log(p/kPa) = (8.23 +/- 0.20) - (10150 +/- 150)/(T/K). The standard sublimation enthalpy of this compound, Delta(sub)H degrees(298) = 206 +/- 4 kJ mol(-1), as derived by second-law elaboration of the experimental data, is proposed. Some structural aspects of C-76 and C-84 crystals were investigated by X-ray analysis. Considerations on the thermodynamic properties of these compounds are also reported.