Computations of low-energy non-icosahedral structures of C-60(6-)

Abstract

Owing to the three-fold degeneracy of the LUMO in C-60, its hexa-anion is not subjected to Jahn-Teller distortions. In contrast to the accepted presumptions, however, computations at the MNDO, AM1, PM3, SAM1, HF/STO-3G, HF/3-21G, and HF/4-31G levels show that the completely relaxed, non-icosahedral cage of C-60(6-) is lower in energy. The computed energy gain varies between 60 and 150 kJ/mol and thus, it is consistently significant (the most sophisticated approach, HF/4-31G, yields 93 kJ/mol). The longest C-C bond in the relaxed structures is at most computed 0.05 Angstrom longer compared to the 5/6 bond in the icosahedral C-60(6-). The symmetry of C-60(6-) is relaxed to D-2. A C-2v isomer is discussed, too.