Temperature-dependent EPR studies on isolated scandium metallofullerenes:: Sc@C82(I, II) and Sc@C84

Two structural isomers of Sc@C-82(I, II) and one isomer of Sc@C-84 have been produced and isolated for the first time. EPR hyperfine spectra together with the UV-vis-NIR absorption spectra indicate that the electronic structures are different between Sc@C-82 isomers I and II. The absorption spectra of these scandium metallofullerenes are different from the other group-3 monometallofullerenes, such as La3+@C-82(3-) and Y3+@C-82(3-). The satellite C-13 hyperfine structure of Sc@C-84 shows fewer structural features than that of Sc@C-82(I), which suggests the cage symmetry of Sc@C-84 is lower than C-2v symmetry of Sc@C-82(I). EPR hyperfine splitting of Sc@C-82(I, II) at room temperature shows that the isotropic hyperfine interaction of Sc@C-82(II) is one-third of that of Sc@C-82(I). One of the main reasons for the large difference of the anisotropic g tensors is due to a difference in excitation energies of the unpaired electron spin of each Sc@C-82 isomer, which is reflected in the HOMO-LUMO gap deduced from the observed absorption spectra.