Theoretical Prediction of Icosahedral U@C20and Analogous Systems with High HOMO–LUMO Gap

Abstract

The electronic structures, bonding, stability, aromaticity, and spectroscopic properties of the endohedral metallofullerenes, M@C20 (M = Pr–, Pa–, Nd, U, Pm+, Np+, Sm2+, Pu2+, Eu3+, Am3+, Gd4+, and Cm4+), have been investigated in a unified and systematic way using relativistic density functional theory (DFT) within the framework of zeroth-order regular approximation. The bare C20 cage with D3d point group transforms to highly symmetrical Ih structure through encapsulation of an f-block metal atom/ion with 6 valence electrons. The calculated values of HOMO–LUMO gap lie in the range of 2.5–4.9 eV (8.8–11.5 eV) at the B3LYP (HF) level. The stability of these metal encapsulated clusters can be attributed to the fulfillment of 26 valence electrons criteria corresponding to the fully occupied 2s2p1d atomic shells, where strong participation of the central metal atom orbitals in the ag, t1u, gu, and hg valence molecular orbitals have been observed.