Hindered Cluster Rotation and 45Sc Hyperfine Splitting Constant in Distonoid Anion Radical Sc3N@C80−, and Spatial Spin−Charge Separation as a General Principle for Anions of Endohedral Fullerenes with Metal-Localized Lowest Unoccupied Molecular Orbitals
journal contributionposted on 31.12.2008, 00:00 by Alexey A. Popov, Lothar Dunsch
DFT calculations of Sc3N@C80 in the neutral and anionic states are performed which revealed that in the neutral state of the nitride clusterfullerene the lowest energy structure has C3 symmetry, while in the anionic and dianionic states the C3v conformer has the lowest energy. Barriers to the cluster rotation inside the cage are also found to increase in the charge states. The 45Sc hyperfine slitting constant, a(Sc), in Sc3N@C80 anion radical is calculated by different theoretical approaches and in different conformations of Sc3N cluster. It is found that a(Sc) is strongly dependent on the cluster orientation with respect to the cage, covering a range form −10 to +25 Gauss at the B3LYP/6-311G*//PBE/TZ2P level of theory. A thorough analysis of the computed values as well as comparison of unrestricted and orbital-restricted calculations revealed that the polarization contribution to a(Sc) is about −10 Gauss and does not depend on the cluster orientation. Dependence of the predicted a(Sc) values on the density functional form (LSDA, BP, PBE, BLYP, OLYP, TPSS, B3LYP, and TPSSh), the basis set, as well as on the scalar-relativistic and spin−orbit corrections were investigated. The analysis of the charge distribution in the Sc3N@C80− anion radical revealed an interesting peculiarity of its electronic structure: while the spin density mostly resides on the cluster, only a slight decrease of its charge is found using both Bader and Mulliken definitions of atomic charges. A set of other endohedral metallofullerenes, including nitride clusterfullerenes Sc3N@C2n (2n = 68, 70, 78) and Y3N@C2n (2n = 78−88), carbide clusterfullerenes Sc2C2@C68, Sc2C2@C82, Sc3C2@C80, Ti2C2@C78, Y2C2@C82, and dimetallofullerenes Sc2@C76, Y2@C82, La2@C2n (2n = 72, 78, 80), was also studied in the neutral and anionic state, and a spatial charge−spin separation is found to be a general rule for all endohedral fullerenes with high contribution of metal atoms to the LUMO.