Theoretical Investigations of LuC: Unexpected Impact of Metal Electronic Configuration toward the Metal-Metal σ-Bond in Fullerene.

Recent experimental works recovered multiformity of lutetium-involved dimetallofullerenes. On the basis of density functional theory (DFT) combined with statistical thermodynamic analyses, the relative stabilities of LuC dimetallofullerene were clarified. Besides the experimentally acknowledged Lu@(51591)-C and Lu@(51575)-C, another four isomers metallofullerenes, Lu@(51580)-C, LuC@(39715)-C, LuC@(39717)-C, and LuC@(39718)-C, are first proposed as thermodynamically stable structures. Interestingly, the geometric relationships among the pristine cages of stable LuC isomers through Stone-Wales transformation or C lose/insertion reveal important clues of the fullerene formation mechanism. The ionic interaction in the stable LuC isomers is revealed, and their valence states are Lu@C or (LuC)@C. In the Lu@C isomers, the results of frontier molecular orbital and natural bond orbital analyses suggest that a Lu-Lu single bond is formed, which is mainly composed of the 6s and 6p orbitals of the Lu atoms. Further analyses of the M@C (M = Sc, Y, La, and Yb) structures disclose the importance of the electron configuration of metal element toward the formation of a single metal-metal bond in C. Moreover, the covalent interaction between the Lu moiety and the C cages is disclosed, which is a supplement to the ionic model.