Sc2S@Cs(10528)-C72: A Dimetallic Sulfide Endohedral Fullerene with a Non Isolated Pentagon Rule Cage

A non isolated pentagon rule metallic sulfide clusterfullerene, Sc2S@C-s(10528)-C-72, has been isolated from a raw mixture of Sc2S@C-2n (n = 35-50) obtained by arc-discharging graphite rods packed with Sc2O3 and graphite powder under an atmosphere of SO2 and helium. Multistage HPLC methods were utilized to isolate and purify the Sc2S@C-72. The purified Sc2S@C-s(10528)-C-72 was characterized by mass spectrometry, UV-vis-NIR absorption spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the C-72 fullerene cage violates the isolated pentagon rule, and the cage symmetry was assigned to C-s(10528)-C-72. The electrochemical behavior of Sc2S@C-s(10528)-C-72 shows a major difference from those of Sc2S@C-s(6)-C-82 and Sc2S@C-3v(8)-C-82 as well as the other metallic clusterfullerenes. Computational studies show that the Sc2S cluster transfers four electrons to the C-72 cage and C-s(10528)-C-72 is the most stable cage isomer for both empty C-72(4-) and Sc2S@C-72, among the many possibilities. The structural differences between the reported fullerenes with C-72 cages are discussed, and it is concluded that both the transfer of four electrons to the cage and the geometrical requirements of the encaged Sc2S cluster play important roles in the stabilization of the C-s(10528)-C-72 cage.