BUCKMINSTERFULLERIDE(1-) SALTS - SYNTHESIS, EPR, AND THE JAHN-TELLER DISTORTION OF C-60-

Synthetic methods are reported for the isolation of a number of buckminsterfulleride(1-) salts. Counterions include cobaltocenium ion, Na(dibenzo-18-crown-6)+, and bis(N-methylimidazole)(tetraphenylporphinato)tin(IV)2+. The EPR spectrum of C60- in frozen solution shows two unusual features. First, there is a counterion-dependent anisotropy observed at low temperatures. This is ascribed to an ellipsoidal distortion induced by ion pairing. It is consistent with, but not directly ascribable to, a static Jahn-Teller distortion. Second, there are two components to the high-temperature spectrum: the broad essentially isotropic, major signal and a narrower ''spike''. The narrower signal is ascribed to thermal population of a low-lying excited state, a natural consequence of the distortion that splits the 2T1u. state into closely spaced 2E and 2A states. In contrast to intuition and to ab initio calculations, the 2E state is lowest in most systems studied to date.