The way of stabilizing non-IPR fullerenes and structural elucidation of C₅₄Cl₈

Recently, a new non-IPR chlorofullerene C⁵⁴C₁₈ was isolated experimentally (Science 2004, 304, 699). To explore the ways to stabilize non-IPR fullerenes, the authors studied all of the possible isomers of C₅₄ fullerene and some of the C₅₄Cl₈ isomers at PM3, B3LYP/3-21G, and B3LYP/6-31G* levels. Combined with analysis of pentagon distributions, bond resonance energies, and steric strains, C ₅₄:540 with the least number of 5/5 bonds was determined to be the thermodynamically best isomer for the C₅₄Cl₈. Based on C₅₄:540, the most probable structure of the experimental C ₅₄Cl₈ was elucidated. The results suggested one of the necessary conditions of stabilizing non-IPR fullerenes: chemical derivatizations of either endohedral complexation or exohedral addition need to sufficiently stabilize all of the kinetically unstable 5/5 bonds of the cages.