Intrafullerene electron transfers in Sm-containing metallofullerenes: Sm@C2n (74 < or = 2n < or = 84).

The electronic properties of Sm-containing metallofullerenes, Sm@C74, Sm@C76 (I, II), Sm@C78, Sm@C80, Sm@C82 (I, II, III) and Sm@C84 (I, II, III), are characterized by UV-Vis-NIR absorption spectroscopy and electron energy-loss spectroscopy (EELS). The UV-Vis-NIR absorption spectra of Sm@C74, Sm@C80, Sm@C82 (I, II, III) and Sm@C84 (I, II) are quite similar to those of the corresponding Ca, Sr, Ba, Eu, Tm, Yb-based metallofullerenes. In contrast, the absorption spectra of Sm@C76 (I, II), Sm@C78 and Sm@C84(III) show a novel feature: the onset for Sm@C78 is observed approximately 2600 nm, which corresponds to a small band gap (approximately 0.5 eV). Furthermore, the oxidation states of Sm atom in the various fullerene cages are investigated by EELS, which reveals that the Sm atom takes +2 oxidation state in the fullerene cages. A probable rationale for the tendency to have the Sm2+ state is presented based on a simple thermochemical cycle model.