STANDARD ENTHALPY OF FORMATION OF BUCKMINSTERFULLERENE

The recent discovery of an efficient synthesis of buckminsterfullerene, C60 has opened the way to the eventual determination of its thermodynamic properties. This paper reports results of energy of combustion measurements made on approximately 125-mg samples of C60 using a specially developed technique to ensure combustion of the small samples in a conventional bomb calorimeter. Energy of combustion measurements on a sample of graphite gave DELTA(c)U-degrees(m)/M = -(32 774.6 +/- 3.7) J g-1, in excellent agreement with earlier results at NIST. For pure C60 a value DELTA(c)U-degrees(m)/M = -(36 123.7 +/- 9.7) J g-1 is obtained. The corresponding standard enthalpy of formation of crystalline C60 is DELTA(f)H-degrees(m). (C60, cr, 298.15 K) = (2422 +/- 14) kJ mol.-1 Using literature values for the enthalpy of sublimation and ideal-gas-phase heat capacity for C60 in conjunction with unpublished solid-phase heat capacity measurements made at NIPER, an ideal gas standard enthalpy of formation DELTA(f)H-degrees(m) (C60, g, 298.15 K) = (2656 +/- 25) kJ mol-1 is derived. That value is listed along with values in the literature estimated using various semiempirical molecular-orbital-type computational methods.