Electronic structure of endohedral Sc@C 82; an ab initio Hartree-Fock analysis

Abstract

The electronic structure of endohedral Sc@C 82 has been studied by different computational techniques. To optimize the geometry of Sc@C 82 and the bare C 82 cage, ab initio Hartree-Fock (HF) calculations in the minimal STO 3G basis have been performed. The split-valence 3–21G ∗ basis set has been used to derive the Sc binding energy and atomic net charges. The optimized position of Sc is strongly off-center. The coordination number of the endohedral atom is six. Sc is located above the 66 bond of a pyracylene unit in the pocket region of C 82 a geometrical arrangement which minimizes the ScC contacts to the carbon atoms of the second coordination sphere. The spatial reorganization process of the carbon atoms in the transition from C 82 to Sc@C 82 are compared with spatial reorganization processes encountered in the transition from pyracylene C 14H 8 to the corresponding dianion C 14H 8 2− and from icosahedral C 60 to the dodeca anion C 60 12−. The excess electrons in the corresponding systems lead to a suppression of the bond-length alternation in the pentagon fragments. The π electronic structure of the different systems has been described by simple ‘resonance’ structures. Furthermore, we have discussed the 13C and 45Sc hyperfine interaction (hfs) in Sc@C 82. The 13C hfs data have been simulated by local spin density and INDO calculations. The present findings are compared with experimental observations and the results of other computational studies.