Increasing Stability of the Fullerenes with the Number of Carbon Atoms: The Experimental Evidence
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- 作者：Aaró ; n Rojas ; Melchor Martí ; nez ; Patricia Amador ; Luis Alfonso Torres
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：August 2, 2007
- 年：2007
- 卷：111
- 期：30
- 页码：9031 - 9035
- 全文大小：244K
- 年卷期：v.111,no.30(August 2, 2007)
- ISSN：1520-5207
文摘
The values of the molar standard enthalpies of formation, 
f
(C76, cr) = (2705.6 ± 37.7) kJ·mol-1, f
(C78, cr) = (2766.5 ± 36.7) kJ·mol-1, and f
(C84, cr) = (2826.6 ± 42.6) kJ·mol-1, were determined fromthe energies of combustion, measured by microcombustion calorimetry on a high-purity sample of the D2isomer of fullerene C76, as well as on a mixture of the two most abundant constitutional isomers of C78(C2v-C78 and D3-C78) and C84 (D2-C84, and D2d-C84). These values, combined with the published data on theenthalpies of sublimation of each cluster, lead to the gas-phase enthalpies of formation, f
(C76, g) =(2911.6 ± 37.9) kJ·mol-1; f
(C78, g) = (2979.3 ± 37.2) kJ·mol-1, and f
(C84, g) = (3051.6 ± 43.0)kJ·mol-1, results that were found to compare well with those reported from density functional theorycalculations. Values of enthalpies of atomization, strain energies, and the average C-C bond energy werealso derived for each fullerene. A decreasing trend in the gas-phase enthalpy of formation and strain energyper carbon atom as the size of the cluster increases is found. This is the first experimental evidence that thesefullerenes become more stable as they become larger. The derived experimental average C-C bond energyEC-C = 461.04 kJ·mol-1 for fullerenes is close to the average bond energy EC-C = 462.8 kJ·mol-1 for polycyclicaromatic hydrocarbons (PAHs).
f (C76, cr) = (2705.6 ± 37.7) kJ·mol-1, f(C78, cr) = (2766.5 ± 36.7) kJ·mol-1, and f (C84, cr) = (2826.6 ± 42.6) kJ·mol-1, were determined fromthe energies of combustion, measured by microcombustion calorimetry on a high-purity sample of the D2isomer of fullerene C76, as well as on a mixture of the two most abundant constitutional isomers of C78(C2v-C78 and D3-C78) and C84 (D2-C84, and D2d-C84). These values, combined with the published data on theenthalpies of sublimation of each cluster, lead to the gas-phase enthalpies of formation, f (C76, g) =(2911.6 ± 37.9) kJ·mol-1; f (C78, g) = (2979.3 ± 37.2) kJ·mol-1, and f (C84, g) = (3051.6 ± 43.0)kJ·mol-1, results that were found to compare well with those reported from density functional theorycalculations. Values of enthalpies of atomization, strain energies, and the average C-C bond energy werealso derived for each fullerene. A decreasing trend in the gas-phase enthalpy of formation and strain energyper carbon atom as the size of the cluster increases is found. This is the first experimental evidence that thesefullerenes become more stable as they become larger. The derived experimental average C-C bond energyEC-C = 461.04 kJ·mol-1 for fullerenes is close to the average bond energy EC-C = 462.8 kJ·mol-1 for polycyclicaromatic hydrocarbons (PAHs).