The Shape of the Sc₂(μ₂-S) Unit Trapped in C₈₂: Crystallographic, Computational, and Electrochemical Studies of the Isomers, Sc₂(μ₂-S)@<i>C</i>_<i>s</i>(6)-C₈₂ and Sc₂(μ₂-S)@<i>C</i>_3<i>v</i>(8)-C₈₂

Abstract

Single-crystal X-ray diffraction studies of Sc₂(μ₂-S)@<i>C</i>_<i>s</i>(6)-C₈₂·Ni^II(OEP)·2C₆H₆ and Sc₂(μ₂-S)@<i>C</i>_3<i>v</i>(8)-C₈₂·Ni^II(OEP)·2C₆H₆ reveal that both contain fully ordered fullerene cages. The crystallographic data for Sc₂(μ₂-S)@<i>C</i>_<i>s</i>(6)-C₈₂·Ni^II(OEP)·2C₆H₆ show two remarkable features: the presence of two slightly different cage sites and a fully ordered molecule Sc₂(μ₂-S)@<i>C</i>_<i>s</i>(6)-C₈₂ in one of these sites. The Sc−S−Sc angles in Sc₂(μ₂-S)@<i>C</i>_<i>s</i>(6)-C₈₂ (113.84(3)°) and Sc₂(μ₂-S)@<i>C</i>_3<i>v</i>(8)-C₈₂ differ (97.34(13)°). 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 C₈₂, the cage stability changes markedly between 0 and 250 K, but the <i>C</i>_<i>s</i>(6)-C₈₂ cage is preferred at temperatures ≥250 °C when using the energies obtained with the free encapsulated model (FEM). However, the <i>C</i>_3<i>v</i>(8)-C₈₂ cage is preferred at temperatures ≥250 °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 Sc₂(μ₂-S) cluster, whereas earlier FEM and RRHO calculations predicted only the <i>C</i>_<i>s</i>(6)-C₈₂ cage is likely to trap the Sc₂(μ₂-O) cluster. We also compare the recently published electrochemistry of the sulfide-containing Sc₂(μ₂-S)@<i>C</i>_<i>s</i>(6)-C₈₂ to that of corresponding oxide-containing Sc₂(μ₂-O)@<i>C</i>_<i>s</i>(6)-C₈₂.