The Shape of the Sc-2(mu(2)-S) Unit Trapped in C-82: Crystallographic, Computational, and Electrochemical Studies of the Isomers, Sc-2(mu(2)-S)@C-s(6)-C-82 and Sc-2(mu(2)-S)@C-3v(8)-C-82

Mary A. Mackey, University of Southern Mississippi
Steven Stevenson, University of Southern Mississippi


Single-crystal X-ray diffraction studies of Sc-2(mu(2)-S)@C-s(6)-C-82 center dot Ni-II(OEP)center dot 2C(6)H(6) and Sc-2(mu(2)-S)@C-3v(8)-C-82 center dot Ni-II(OEP)center dot 2C(6)H(6) reveal that both contain fully ordered fullerene cages. The crystallographic data for Sc-2(mu(2)-S)@C-s(6)-C-82 center dot Ni-II(OEP)center dot 2C(6)H(6) show two remarkable features: the presence of two slightly different cage sites and a fully ordered molecule Sc-2(mu(2)-S)@C-s(6)-C-82 in one of these sites. The Sc-S-Sc angles in Sc-2(mu(2)-S)@C-s(6)-C-82 (113.84(3)degrees) and Sc-2(mu(2)-S)@C-3v(8)-C-82 differ (97.34(13)degrees). This is the first case where the nature and structure of the fullerene cage isomer exerts a demonstrable effect on the geometry of the cluster contained within. Computational studies have shown that, among the nine isomers that follow the isolated pentagon rule for C-82, the cage stability changes markedly between 0 and 250 K, but the C-s(6)-C-82 cage is preferred at temperatures >= 250 degrees C when using the energies obtained with the free encapsulated model (FEM). However, the C-3v(8)-C-82 cage is preferred at temperatures >= 250 degrees C using the energies obtained by rigid rotor-harmonic oscillator (RRHO) approximation. These results corroborate the fact that both cages are observed and likely to trap the Sc-2(mu(2)-S) cluster, whereas earlier FEM and RRHO calculations predicted only the C-s(6)-C-82 cage is likely to trap the Sc-2(mu(2)-O) cluster. We also compare the recently published electrochemistry of the sulfide-containing Sc-2(mu(2)-S)@C-s(6)-C-82 to that of corresponding oxide-containing Sc-2(mu(2)-O)@C-s(6)-C-82.