Lu-Lu Bond in Lu₂@C₆₀ Metallofullerenes

Abstract

This study on Lu2@C60 isomers provides insights into the metal–metal bond through the confinement effect of fullerene cages. Density functional theory calculations were used to study the nature of the Lu-Lu bond in two stable endohedral metallofullerenes (EMFs), Lu2@C2v_C60 and Lu2@Ih_C60, both with negative endohedral energy. These two isomers are geometrically connected through a simple Stone–Wales (SW) transformation. The electronic configuration of (Lu2)4+@C604− was also confirmed, leading to the formation of a two-center two-electron (2c–2e) Lu-Lu σ single bond. By comparing the Lu-Lu bonds in Lu2@C60 with those in acknowledged Lu2@C2n, the smaller C60 fullerene compressed the geometry of Lu2 resulting in a much shorter Lu-Lu bond length. However, the Lu-Lu bond strength is slightly weaker in Lu2@C60 than that in large fullerenes, as the Lu-Lu bond in C60 is likely a p-p σ bond with an above the 40% contribution of p orbital and a strong metal–cage interaction. Additionally, the vis-NIR spectra of Lu2@C2v_C60 and Lu2@Ih_C60 were simulated, which could provide valuable information for future experimental studies on Lu-based EMFs.

Keywords

• endohedral metallofullerenes
• metal–metal bond
• size effect