Theoretical Investigations of Lu2C84: 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 Lu2C84 dimetallofullerene were clarified. Besides the experimentally acknowledged Lu2@D2d(51591)-C84 and Lu2@C2v(51575)-C84, another four isomers metallofullerenes, Lu2@C1(51580)-C84, Lu2C2@Cs(39715)-C82, Lu2C2@C3v(39717)-C82, and Lu2C2@C2v(39718)-C82, are first proposed as thermodynamically stable structures. Interestingly, the geometric relationships among the pristine cages of stable Lu2C84 isomers through Stone-Wales transformation or C2 lose/insertion reveal important clues of the fullerene formation mechanism. The ionic interaction in the stable Lu2C84 isomers is revealed, and their valence states are Lu24+@C844- or (Lu2C2)4+@C824-. In the Lu2@C84 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 M2@C84 (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 C84. Moreover, the covalent interaction between the Lu2 moiety and the C84 cages is disclosed, which is a supplement to the ionic model.