The Quadratic p 3 ⊗ h Jahn–Teller System as a Model for the C 60 3− Anion

The fullerene trianion, C60 3−, and the compounds associated with it are known to have properties that differ significantly from the other fullerene ions. For example, compounds of the form A3C60 (where A is an alkali metal) which contain this ion, are known to be superconductors up to around 40K, whereas the alkali metal fullerenes containing C60 2− and C60 4− are found to be insulators, properties often attributed to the Jahn–Teller effect. In spite of this, little work has been undertaken analysing the Jahn–Teller effect in the trianion. In this work, the symmetry reduction caused by this effect is investigated by introducing quadratic terms into the Hamiltonian to model the Jahn–Teller interaction. It is found that, unlike the previously investigated ions of C60, an electronic degeneracy remains if the molecular distortion were to be described by either the D 3d or D 5d point groups. Thus, a further reduction in symmetry is expected, and it is found that the distorted molecule is actually described by either the C 2h or D 2h group. A distortion of C 2h symmetry in a fullerene molecule has previously undergone little analysis, and so it is this that is then investigated by considering a set of distortional axes relating to the minimum energy wells formed under a quadratic interaction.