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

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