Metal Sulfide in a C82 Fullerene Cage: A New Form of Endohedral Clusterfullerenes

The row of endohedral fullerenes is extended by a new type of sulfur-containing clusterfullerenes: the metal sulfide (M2S) has been stabilized within a fullerene cage for the first time. The new sulfur-containing clusterfullerenes M2S@C-82-C-3v(8) have been isolated for a variety of metals (M = Sc, Y, Dy, and Lu). The UV-vis-NIR, electrochemical, and FTIR spectroscopic characterization and extended DFT calculations point to a close similarity of the M2S@C-82 cage isomeric and electronic structure to that of the carbide clusterfullerenes M2C2@C-2n. The bonding in M2S@C-82 is studied in detail by molecular orbital analysis as well as with the use of quantum theory of atom-in-molecules (QTAIM) and electron localization function (ELF) approaches. The metal sulfide cluster formally transfers four electrons to the carbon cage, and metal-sulfur and metal-carbon cage bonds with a high degree of covalency are formed. Molecular dynamics simulations show that Sc2S cluster exhibits an almost free rotation around the C-3 axis of the carbon cage, resulting thus in a single line Sc-45 NMR spectrum.