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

Synthetic methods are reported for the isolation of a number of buckmi nsterfulleride(1-) salts. Counterions include cobaltocenium ion, Na(di benzo-18-crown-6)+, and -methylimidazole)(tetraphenylporphinato)tin(IV )2+. The EPR spectrum of C60- in frozen solution shows two unusual fea tures. First, there is a counterion-dependent anisotropy observed at l ow 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 t hermal population of a low-lying excited state, a natural consequence of the distortion that splits the 2T1u. state into closely spaced 2E a nd 2A states. In contrast to intuition and to ab initio calculations, the 2E state is lowest in most systems studied to date.