Sc<sub>2</sub>S@<i>C<sub>s</sub></i>(10528)-C<sub>72</sub>: A Dimetallic Sulfide Endohedral Fullerene with a Non Isolated Pentagon Rule Cage

A non isolated pentagon rule metallic sulfide clusterfullerene, Sc<sub>2</sub>S@<i>C</i><sub><i>s</i></sub>(10528)-C<sub>72</sub>, has been isolated from a raw mixture of Sc<sub>2</sub>S@C<sub>2<i>n</i></sub> (<i>n</i> = 35–50) obtained by arc-discharging graphite rods packed with Sc<sub>2</sub>O<sub>3</sub> and graphite powder under an atmosphere of SO<sub>2</sub> and helium. Multistage HPLC methods were utilized to isolate and purify the Sc<sub>2</sub>S@C<sub>72</sub>. The purified Sc<sub>2</sub>S@<i>C</i><sub><i>s</i></sub>(10528)-C<sub>72</sub> 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<sub>72</sub> fullerene cage violates the isolated pentagon rule, and the cage symmetry was assigned to <i>C</i><sub><i>s</i></sub>(10528)-C<sub>72</sub>. The electrochemical behavior of Sc<sub>2</sub>S@<i>C</i><sub><i>s</i></sub>(10528)-C<sub>72</sub> shows a major difference from those of Sc<sub>2</sub>S@<i>C</i><sub><i>s</i></sub>(6)-C<sub>82</sub> and Sc<sub>2</sub>S@<i>C</i><sub>3<i>v</i></sub>(8)-C<sub>82</sub> as well as the other metallic clusterfullerenes. Computational studies show that the Sc<sub>2</sub>S cluster transfers four electrons to the C<sub>72</sub> cage and <i>C</i><sub><i>s</i></sub>(10528)-C<sub>72</sub> is the most stable cage isomer for both empty C<sub>72</sub><sup>4–</sup> and Sc<sub>2</sub>S@C<sub>72</sub>, among the many possibilities. The structural differences between the reported fullerenes with C<sub>72</sub> cages are discussed, and it is concluded that both the transfer of four electrons to the cage and the geometrical requirements of the encaged Sc<sub>2</sub>S cluster play important roles in the stabilization of the <i>C</i><sub><i>s</i></sub>(10528)-C<sub>72</sub> cage.