Electron delocalization and dimerization in solid C₅₉N doped C₆₀ fullerene

Electron spin resonance and ab initio electronic structure calculations show an intricate relation between molecular rotation and chemical bonding in the dilute solid solution C₅₉N:C₆₀. The unpaired electron of C₅₉N is delocalized over several C₆₀ molecules above 700 K, while at lower temperatures it remains localized within short range. The data suggest that below 350 K rigid C₅₉N‐C₆₀ heterodimers are formed in thermodynamic equilibrium with dissociated rotating molecules. The structural fluctuations between heterodimers and dissociated molecules are accompanied by simultaneous electron spin transfer between C₆₀ and C₅₉N molecules. The calculation confirms that in the C₅₉N‐C₆₀ heterodimer the spin density resides mostly on the C₆₀ moiety, while it is almost entirely on C₅₉N in the dissociated case.