ESR STUDY OF THE ELECTRONIC-STRUCTURES OF METALLOFULLERENES - A COMPARISON BETWEEN LA-AT-C-82 AND SC-AT-C-82

The line widths of the hyperfine components of ESR spectra of La@C-82 and Sc@C-82 in CS2 and toluene solutions have been measured as a function of temperature. The extent of line broadening due not only to the insufficient rotational averaging of g and hyperfine tensors but also to the spin-rotation coupling interaction have been determined. The values of anisotropy for the g and hyperfine tensors are deduced by analysis according to Kivelson's formalism for these line broadening mechanisms. Although the two spectra for La@C-82 and Sc@C-82 in solution at room temperature look similar to each other, the different electronic structure for each endohedral metal is reflected in their differing values for the anisotropy of the g and hyperfine tensors. The electronic structures of La@C-82 and Sc@C-82 are discussed comparatively in terms of a theoretical interpretation for the anisotropic correction of the g factor and the hyperfine coupling constant. The results exhibit different electronic structures for La@C-82 and Sc@C-82; the radical electron is assigned to a pi orbital of the C-82 cage for La@C-82 but to a d orbital of the metal for Sc@C-82.