Dy@ C₆₀: Evidence for endohedral structure and electron transfer

In view of the lack of information on the structure of M@C₆₀ (M: alkaline earth and lanthanide metal) because of its instability and difficulties in purifying it, we have carried out and report here some structural investigations of Dy@C₆₀. We obtained a pure sample of Dy@C₆₀ by high-performance liquid chromatography with aniline as an eluent, and studied it by Dy L_III-edge x-ray-absorption fine structure and Raman scattering. Our results show conclusively that the structure is endohedral (with the metal inside the C₆₀ cage) and that electron transfer takes place between Dy and C₆₀. The Dy in Dy@C₆₀ is located at an off-center position 1.25-1.30 Å from the center of the C₆₀ cage. The valence of the Dy is shown to be +3 on the basis of a Dy L_III-edge x-ray absorption near edge structure study. The A_g(2) Raman peak also shows that three electrons have been transferred from the Dy atom to the C₆₀ cage. The UV-VIS-IR spectrum suggests that the highest-occupied-lowest-unoccupied-molecular-orbital gap is small.