(formula presented) Evidence for endohedral structure and electron transfer

In view of the lack of information on the structure of (formula presented) (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 (formula presented) We obtained a pure sample of (formula presented) by high-performance liquid chromatography with aniline as an eluent, and studied it by Dy (formula presented)-edge x-ray-absorption fine structure and Raman scattering. Our results show conclusively that the structure is endohedral (with the metal inside the (formula presented) cage) and that electron transfer takes place between Dy and (formula presented) The Dy in (formula presented) is located at an off-center position 1.25–1.30 Å from the center of the (formula presented) cage. The valence of the Dy is shown to be +3 on the basis of a Dy (formula presented)-edge x-ray absorption near edge structure study. The (formula presented) Raman peak also shows that three electrons have been transferred from the Dy atom to the (formula presented) cage. The UV-VIS-IR spectrum suggests that the highest–occupied–lowest-unoccupied-molecular-orbital gap is small.