ring are essentially in a neutral state. The experimental studies on the structure and optical properties of Li + @C60 in also obtained the conclusion that C60 is almost electrically neutral, which confirms the electron-accepting feature of C18 ring similar to C60, because even when combined with cations, they can still keep their electrons from losing. The fairly small Wiberg bond order between M + and C atoms in C18 moiety [BO(M + C) max ] reveals that the contribution of electron-sharing effect to M + C18 binding can be neglected.