Significant Roles of a Particularly Stable Two-Center Two-Electron Lu-Lu σ Bond in Lu2@C86: Electronic Structure of Lu and Radius of Lu2.

Abstract

There is still dispute over the stability of endohedral metallofullerenes (EMFs) M2C2n, and recently, multiform lutetium-based dimetallofullerenes have been dropped in experiments. The thermodynamic stabilities of Lu2C86 EMFs are revealed by density functional theory (DFT) in conjunction with statistical thermodynamic analyses. Inevitably, besides the experimentally reported Lu2@C2v(63751)-C86, Lu2@Cs(63750)-C86, and Lu2@Cs(63757)-C86, other three metal carbide clusterfullerenes, Lu2C2@D2d(51591)-C84, Lu2C2@C1(51383)-C84, and Lu2C2@Cs(id207430)-C84, rather than Lu2@C86 are first characterized as thermodynamically stable isomers of Lu2C86. Specially, the Cs(id207430)-C84 is a newly non-classical fullerene containing one heptagon, which is stabilized via encaging Lu2C2. Another interesting phenomenon is that the outer fullerene cages of thermodynamically stable Lu2C82-88 molecules are geometrically connected through C2 addition/loss and Stone-Wales (SW) transformation, suggesting a special relationship between thermodynamic stabilities and geometries of Lu2C82-88 EMFs. Furthermore, the electronic configurations of (Lu2)4+@C864- and (Lu2C2)4+@C844- were confirmed. A significantly stable two-center two-electron (2c-2e) Lu-Lu σ single bond is formed in Lu2@C86. By comparing M-M bonds in M2@C2v(63751)-C86 (M = Sc, Y, La, and Lu), two significant factors, the valence atomic orbital (ns) of metal atoms and radius of M2+, are found to determine the stability of the M-M bond in the C2v(63751)-C86. Additionally, the simulated UV-vis-NIR spectra of thermodynamically stable Lu2C86 isomers were simulated, which further disclose their electronic features.