Sc₂S@C_s(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)-C₇₂, 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@C₇₂. The purified Sc₂S@C_s(10528)-C₇₂ 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 C₇₂ fullerene cage violates the isolated pentagon rule, and the cage symmetry was assigned to C_s(10528)-C₇₂. The electrochemical behavior of Sc₂S@C_s(10528)-C₇₂ shows a major difference from those of Sc₂S@C_s(6)-C₈₂ and Sc₂S@C_3v(8)-C₈₂ as well as the other metallic clusterfullerenes. Computational studies show that the Sc₂S cluster transfers four electrons to the C₇₂ cage and C_s(10528)-C₇₂ is the most stable cage isomer for both empty C₇₂^4– and Sc₂S@C₇₂, among the many possibilities. The structural differences between the reported fullerenes with C₇₂ 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)-C₇₂ cage.