A Density Functional Study of Ce@C₈₂:  Explanation of the Ce Preferential Bonding Site

Abstract

Ce has been found experimentally to be preferentially incorporated into the C82 isomer of C2v symmetry as have other lanthanoids in M@C82 (M = La, Pr, Nd, etc.). We have investigated the underlying reason for this preference by calculating structural and electronic properties of Ce@C82 using density functional theory. The ground-state structure of Ce@C82 is found to have the cerium atom attached to the six-membered ring on the C2 axis of the C82-C2v cage, and the encapsulated atom is found to perturb the carbon cage due to chemical bonding. We have found Ce to favor this C2v chemisorption site in C82 by 0.62 eV compared to other positions on the inside wall of the cage. The specific preference of the metal atom to this six-membered ring is explained through electronic structure analysis, which reveals strong hybridization between the d orbitals of cerium and the pi orbitals of the cage that is particularly favorable for this chemisorption site. We propose that this symmetry dictated interaction between the cage and the lanthanide d orbital plays a crucial role when C82 forms in the presence of Ce to produce Ce@C82 and is also more generally applicable for the formation of other lanthanoid M@C82 molecules. Our theoretical computations are the first to explain this well-established fact. Last, the vibrational spectrum of Ce@C82 has been simulated and analyzed to gain insight into the metal-cage vibrations.

The Unanticipated Dimerization of Ce@C2v(9)‐C82 upon Co‐crystallization with Ni(octaethylporphyrin) and Comparison with Monomeric M@C2v(9)‐C82 (M = La, Sc, and Y)

“…[14][15][16] Prior studies of Ce@C 2v (9)-C 82 have not uncovered any evidenceo fd imerization of this molecule. [28] Ther esultsp resented herein on the SOMO spin density and pyramidalization (see Ta bleS 3i nt he Supporting Information) show very similar results for Ce@C 2v (9)-C 82 and La@C 2v (9)-C 82 .C onsequently,i ti sq uite re- markable to see such as triking differencei nt he formation of ad imer for Ce@C 2v (9)-C 82 and am onomer for La@C 2v (9)-C 82 after co-crystallization with Ni(OEP). [11,23,24] Previous computational studies have not suggested any unusual features in the electronic structure of monomeric Ce@C 2v (9)-C 82 that would cause dimerization.…”

Metal-Cage Bonding, Molecular Structures and Vibrational Spectra of Endohedral Fullerenes: Bridging Experiment and Theory

“…DFT calculations of vibrational spectra of M@C 82 endohedral fullerenes were performed by several groups; [186][187][188][189] vibrational density of states were also calculated by Kemner and Zerbetto with the use of molecular dynamics calculations. 190 Kobayashi and Nagase reported B3LYP vibrational calculations for La@C 82 based on C 2v (9) cage isomer, 188 which afforded the frequencies of 159 cm −1 for a displacement along C 2 axis (A 1 symmetry type, "longitudal" mode) and 30 cm −1 and 27 cm −1 for two "latteral" modes (B 2 and B 1 symmetry, respectively), in reasonable agreement with experimental data.…”

Theoretical study on the smallest endohedral metallofullerenes: TM@C20 (TM = Ce and Gd)

“…Thus, it is very important to explore the structural, electronic, and vibrational properties of the fullerene C 20 and its endohedral metallofullerene. Additionally, previous studies have reported both experimentally and theoretically that the endohedral metallofullerenes containing Ce and Gd atoms may produce some novel physical and chemical properties [40][41][42][43][44][45][46][47][48][49][50][51][52] such as electrical conductance, magnetism, transport behavior, and nonlinear optical properties, etc. Moreover, the optical transition occurring due to the crystal field effect of the cage on the unfilled f orbitals of these atoms leads to the possibility of producing lasers out of metallofullerenes; and the conductivity of the solid metallofullerenes depends upon the electron donor capacity of the encapsulated atom.…”