On-Ball Doping of Fullerenes: The Electronic Structure of $C_{59}$N Dimers from Experiment and Theory

We present the first studies of the electronic structure of the heterofullerene $({\mathrm{C}}_{59}\mathrm{N}{)}_2$ using electron energy-loss spectroscopy in transmission, photoemission spectroscopy, and density functional theory calculations. Both the C 1s excitation spectra and valence band photoemission show negligible occupation of the C-derived lowest unoccupied electronic states and indicate localization of the excess electrons at the N atoms. The experimental results, together with the detailed analysis of our theoretical data, provide compelling evidence for the chemical picture of a triply coordinated N atom with a lone pair in each heterofullerene unit, and confirm the theoretically predicted “6,6 closed” structure for the dimer.