Divalent metals can reside on bonds in fullerenes

Abstract

DFT calculations consistently suggest that a lanthanide will sit on either the 6/6 bond inside C₆₀ having a divalent state or the hexagonal center having a trivalent state. Some lanthanides can stay only above the 6/6 bond inside C₆₀ to form stabilized structures, despite the greatly reduced metal–cage coordination numbers. The preference for C–C bonds by a divalent metal has been confirmed by revisiting the structures of Yb@C_2v(3)-C₈₀, Yb@C_s(6)-C₈₂ and Yb@C_2v(9)-C₈₂, for which the calculations suggest that the Yb atoms are indeed situated above the C–C bonds, close to the reported structures obtained by single crystal XRD experiments. The result will guide the characterization of structures and electronic structures of endohedral metallofullerenes (EMFs), especially C₆₀ mono-EMFs, in the future.