Lanthanide metals in the boron cages: Computational prediction of M@B-n (M=Eu, Gd; n=38, 40)

Endohedral metalloborofullerenes (EMBFs) are novel boron analogues of the famous endohedral metallofullerenes (EMFs). Many EMBFs have been proposed by theoretical calculations thus far. However, in sharp contrast to EMFs, which trap most of the lanthanides with f electrons inside the cages, the corresponding lanthanide-based EMBFs have never been reported. In this work, the encapsulation of Eu and Gd in the B-38 and B-40 fullerenes was studied by means of density functional theory calculations. Our results revealed that Gd@B-38((9)A), Eu@B-40(B-8(2)), and Gd@B-40((7)A) all favor the endohedral configuration, and the electronic structures can be described as Gd3+@ B383-, Eu2+@ B402-, and Gd3+@ B403- with jailed f electron spins. The large binding energies and sizable HOMO-LUMO gaps suggest that they may be achieved experimentally. They feature sigma and double aromaticity, and their excellent stabilities were confirmed by the Born-Oppenheimer molecular dynamics simulations. Finally, the infrared and UV/vis spectra were simulated to assist experimental characterization.