Overlooked Effects of La-4f Orbitals in Endohedral Metallofullerenes

For endohedral metallofullerenes (EMFs), a central issue is how to correctlydescribe the intracluster and metal-cage interactions, which are critical for understanding theirstructures, stabilities, and various properties. In this work, density functional theory calculationswere carried out for 13 La-based EMFs covering all four reported types and a rather wide cage sizerange (C32-C104). The results reveal that the usually core-like lanthanide 4f subshell may play acritical role in the structural characteristics, energetic stabilities, frontier orbital energy levels, metalcharges, and chemical reactivities of these endofullerenes. Regardless of the encapsulated forms,the La-4f contributions to the chemical bonding and structural stability increase with the reducedcage sizes because of the gradually enhanced cage confinement. The combination of metal-to-nonmetal charge transfer and compression of the cage cavity exposes and effectively activates theotherwise chemically inert 4f orbitals. By disclosing the important role of long-neglected metalorbitals inside fullerenes, the current work not only deepens our understanding of EMFs, but alsoprovides new insights into the chemical bondings in general confined spaces at the subnanometer scale.