The structures of three structural isomers of SC2@C-84(I, II, III) have been determined by C-13 NMR and have C-s, C-2v, and D-2d point group symmetry, respectively. By IR measurements, we have determined that the peaks below 110 cm(-1) originate from the scandium-cage vibrational modes based on temperature-dependent IR experiments. Line broadenings of the Sc-cage modes below 110 cm(-1) are quite different from those of the C-84 (empty) cage modes in far-IR spectra. Sc-cage vibrational modes below 300 cm(-1) in Raman spectra are also identified. The force constants of the Sc-cage vibrations based on a linear three-mass-oscillator model indicate that the charge state of Sc atoms are close to +2.