Structure and stability of covalently bonded polyfulleride ions in AxC60 salts

A comparative study of stabilities is presented for a variety of (C60n−)p polyanions. Formation enthalpies of dimers and monomers were determined from those of AM1 optimized RmC60n− monomers using thermochemical considerations. In contrast to cycloadduct polymers, singly bonded polymers become more stable with increasing charge and a crossover occurs at around n=3. Geometries were analyzed in terms of bond and charge distributions. The polyanion geometries of Na2RbC60 and Na4C60 salts are in agreement with X-ray results.