School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China.
J Comput Chem. 2010 Jun;31(8):1715-21. doi: 10.1002/jcc.21459.
Nonclassical fullerenes with heptagon(s) and their derivatives have attracted increasing attention, and the studies on them are performing to enrich the chemistry of carbon. Density functional theory calculations are performed on nonclassical fullerenes C(n) (n = 46, 48, 50, and 52) to give insight into their structures and stability. The calculated results demonstrate that the classical isomers generally satisfy the pentagon adjacency penalty rule. However, the nonclassical isomers with a heptagon are more energetically favorable than the classical ones with the same number of pentagon-pentagon bonds (B(55) bonds), and many of them are even more stable than some classical isomers with fewer B(55) bonds. The nonclassical isomers with the lowest energy are higher in energy than the classical ones with the lowest energy, because they have more B(55) bonds. Generally, the HOMO-LUMO gaps of the former are larger than those of the latter. The sphericity and asphericity are unable to rationalize the unique stability of the nonclassical fullerenes with a heptagon. The pyramidization angles of the vertices shared by two pentagons and one heptagon are smaller than those of the vertices shared by two pentagons and one hexagon. It is concluded that the strain in the fused pentagons can be released by the adjacent heptagons partly, and consequently, it is a common phenomenon for nonclassical fullerenes to violate the pentagon adjacent penalty rule. These findings are heuristic and conducive to search energetically favorable isomers of C(n), especially as n is 62, 64, 66, and 68, respectively.
具有七边形的非经典富勒烯及其衍生物引起了越来越多的关注，对它们的研究正在进行中，以丰富碳化学。本文通过密度泛函理论计算研究了非经典富勒烯 C(n)（n=46、48、50 和 52），以深入了解它们的结构和稳定性。计算结果表明，经典异构体通常满足五边形相邻罚则。然而，具有七边形的非经典异构体比具有相同数量的五边形-五边形键（B(55)键）的经典异构体更具能量优势，其中许多异构体甚至比具有较少 B(55)键的一些经典异构体更稳定。能量最低的非经典异构体比能量最低的经典异构体能量更高，因为它们具有更多的 B(55)键。一般来说，前者的 HOMO-LUMO 能隙大于后者。球度和非球度不能合理地解释具有七边形的非经典富勒烯的独特稳定性。由两个五边形和一个七边形共享的顶点的金字塔化角度小于由两个五边形和一个六边形共享的顶点的金字塔化角度。结论是，融合五边形中的应变可以部分地被相邻的七边形释放，因此，非经典富勒烯违反五边形相邻罚则是常见现象。这些发现具有启发性，有助于搜索 C(n)的能量有利异构体，特别是当 n 分别为 62、64、66 和 68 时。
