Smallest Endohedral Metallofullerenes [Mg@C20]n (n = 4, 2, 0, −2, and −4): Endo-Ionic Interaction in Superatoms

This work reports a series of endohedral metallofullerene superatoms [Mg@C20]n, where n = 4, 2, 0, −2, and −4. It was found that Mg transfers virtually all of its 3s electrons to the C20 shell, resulting in the ionic states of Mg2+@[C20]n−2. Detailed calculations revealed that the superatomic electronic configuration of these clusters is 1S21P61D101F4–n. The first nine superatomic molecular orbitals (SAMOs), 1S21P61D10, housed with 18 electrons, are largely based on [C20]n−2 with small contributions from magnesium, while the outmost SAMOs, 1F4–n, with 4 – n extra electrons, reside solely on [C20]n−2. The interaction between the Mg2+ ion and [C20]n−2 was found to be predominately ionic in character. Furthermore, ultraviolet–visible spectra provide a theoretical basis for fingerprinting these clusters. It is hoped that this work will encourage the synthetic pursuit of these smallest superatomic systems.