Yang and co-workers also made a systematic study on lanthanide metallofullerenes from the standpoint of Vis–NIR absorption spectra ( Ding and Yang, 1997) together with their HPLC elution behavior ( Huang and Yang, 1988). It is interesting to note that the HPLC retention times of 82 (Ln = Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Lu) are similar to each other but are different from those of 82 (Ln = Sm, Eu, Tm, Yb) which are also almost the same as each other ( Kikuchi et al., 1997 Sueki et al., 1997). Judging from the similarity on the absorption spectra, 82 (Ln = Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Lu) metallofullerenes have 3+ charge state similar to 82 and 82, whereas the charge state of 82 (Ln = Sm, Eu, Tm, Yb) is 2+ as that of 82. UV–Vis–NIR absorption spectra of (A) 82 (I–IV), (B) 84(I, II), and (C) 82(I) for comparison. Furthermore, the absorption spectrum of 82 (IV) was found to be similar to that of 82 (I), indicating that the Ca and Sc atoms are trapped within the same structural isomer having the same oxidation state of 2+.įigure 22. The absorption spectra of the three isomers (A, B, C) of 82 are almost exactly the same as three structural isomers (III, I, IV) of 82, respectively, suggesting that each isomer shares the same isomer structure. A similar observation has been reported for the three structural isomers of 82 (A, B, C) ( Dunsch et al., 1997 Kirbach and Dunsch, 1996). Such an example has been found for the four structural isomers of 82 (I–IV) ( Xu et al., 1996) ( Figure 22). Similar to the group 3 case, the absorption spectra of structural isomers of group 2 metallofullerenes also differ from each other. This is due to the fact that the charge state of the encaged metal atoms for these group 2 metallofullerenes is 2+ rather than 3+. Figure 22 shows the UV–Vis–NIR absorption spectra of major isomers of 82 ( Dennis and Shinohara, 1997a,b, 1998 Dennis et al., 1998 Nakane et al., 1998 Xu et al., 1996).

The absorption spectra of group 2 metallofullerenes are quite different from those of group 3 metallofullerenes. However, the absorption spectra of the C 82 based metallofullerenes containing the divalent lanthanide elements (i.e., Sm, Eu, Tm, and Yb) ( Kikuchi et al., 1997 Kirbach and Dunsch, 1996 Okazaki et al., 2000) are different from those of 82, 82 and 82 but are similar to that of 82 in that the sharp absorption peak at 1,000 nm are missing in these divalent metallofullerenes. The UV–Vis–NIR absorption spectra of many mono-metallofullerenes encapsulating lanthanide elements, 82 ( Ln = Ce–Nd, Gd–Er, Lu) ( Ding et al., 1996b Suzuki et al., 1996), Pr ( Ding and Yang, 1996 Shinohara et al., 1994b), Nd ( Ding et al., 1996a), Gd ( Kikuchi et al., 1994c Shinohara et al., 1994b), Tb ( Shi et al., 2003), Dy (Kikuchi et al, 1998 Tagmatarchis and Shinohara, 2000), Ho ( Knapp et al., 1998 W Wang et al., 1997), Er ( Ito et al., 2007a,b Kikuchi et al, 1998), Lu ( Knapp et al., 1998)), are similar to those of 82 and 82. As described in Section 4.3.2, the charge state of Sc 82 2− (divalency) is different from those of La 82 3− and Y 82 3− (trivalency) ( Hino et al., 1993 Nagase and Kobayashi, 1993 Takata et al., 1995). The spectrum of 82 is very different from those of 82 and 82, indicating that the electronic structure of 82 is different from those of 82 and 82. Figure 20 shows UV–Vis–NIR absorption spectra for the isolated group 3 metallofullerenes: 82 ( Kikuchi et al., 1993 Yamamoto et al., 1994a), 82 ( Kikuchi et al., 1994b) and 82 ( Inakuma et al., 1995) in carbon disulfide solution.

Absorbance spectra