Temperature-Dependent EPR Studies on Isolated Scandium Metallofullerenes: Sc@C_(82)(I, II) and Sc@C_(84)

摘要

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 La~(3+)@C_(82)~(3-) and Y~(3+)@C_(82)~(3-). The satellite ~(13)C 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.