The electronic and vibrational structure of endohedral Tm3N@C80 (I) fullerene -: Proof of an encaged Tm3+

The electronic and vibrational structure of the nitride clusterfullerene Tm3N@C-80 (I) was investigated by cyclic voltammetry, FTIR, Raman, and X-ray photoemission spectroscopy. The electrochemical energy gap of Tm3N@C-80 (I) is 1.99 V, which is 0.13 V larger than that of Sc3N@C-80 (I). FTIR spectroscopy showed that the C-80:7 (I-h,) cages in Tm3N@C-80 (I), Er3N@C-80 (I), Ho3N@C-80 (1), Tb3N@C-80 (I), Gd3N@C-80 (I), and Y3N@C-80 (I) have the same bond order. The analysis of low-energy Raman spectra points to two uniform force constants which can be used to describe the interaction between the encaged nitride cluster and the C-80:7 (I-h) cage in M3N@C-80 (I) (M = Tm, Er, Ho, Tb, Gd, and Y). Because the M3N-C-80 bond strength is strongly dependent on the charge of the metal ions, this is a direct hint for a 3+ formal valence state of the metal ions in these nitride clusterfullerene series, including Tm3N@C-80 (I). Photoemission spectra of the Tm 4d core level and the Tm 4f valence electrons provided a direct proof for a (4f) 12 electronic configuration of the encapsulated thulium. In conclusion, thulium in Tm3N@C-80 (I) has a formal electronic ground state of +3, in contrast to the +2 state found in Tm@C-82. It is demonstrated that the valence state of metal atoms encaged in fullerenes can be controlled by the chemical composition of the endohedral fullerene.