title: The electronic and vibrational structure of endohedral Tm3N@C80 (I) fullerene--proof of an encaged Tm3+.
abstract: The electronic and vibrational structure of the nitride clusterfullerene Tm3N@C80 (I) was investigated by cyclic voltammetry, FTIR, Raman, and X-ray photoemission spectroscopy. The electrochemical energy gap of Tm3N@C80 (I) is 1.99 V, which is 0.13 V larger than that of Sc3N@C80 (I). FTIR spectroscopy showed that the C80:7 (I(h)) cages in Tm3N@C80 (I), Er3N@C80 (I), Ho3N@C80 (I), Tb3N@C80 (I), Gd3N@C80 (I), and Y3N@C80 (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 C80:7 (I(h)) cage in M3N@C80 (I) (M = Tm, Er, Ho, Tb, Gd, and Y). Because the M3N-C80 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@C80 (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@C80 (I) has a formal electronic ground state of +3, in contrast to the +2 state found in Tm@C82. It is demonstrated that the valence state of metal atoms encaged in fullerenes can be controlled by the chemical composition of the endohedral fullerene.
authors.affiliation: Leibniz-Institute for Solid State and Materials Research Dresden, Institute of Solid State Research, Group of Electrochemistry and Conducting Polymers, P. O. box 27 01 16, D-01171 Dresden, Germany. m.krause@ifw-dresden.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Krause
authors.forename: Xianjie
authors.initials: X
authors.lastname: Liu
authors.forename: Joanna
authors.initials: J
authors.lastname: Wong
authors.forename: Thomas
authors.initials: T
authors.lastname: Pichler
authors.forename: Martin
authors.initials: M
authors.lastname: Knupfer
authors.forename: Lothar
authors.initials: L
authors.lastname: Dunsch