Sc₂O@<i>C</i>_2<i>v</i>(5)‑C₈₀: Dimetallic Oxide Cluster Inside a C₈₀ Fullerene Cage

Abstract

A new oxide cluster fullerene, Sc₂O@<i>C</i>_2<i>v</i>(5)-C₈₀, has been isolated and characterized by mass spectrometry, UV–vis–NIR absorption spectroscopy, cyclic voltammetry, ⁴⁵Sc NMR, DFT calculations, and single crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the cage symmetry was assigned to <i>C</i>_2<i>v</i>(5)-C₈₀ and suggests that the Sc₂O cluster is ordered inside the cage. The crystallographic data further reveals that the Sc1–O–Sc2 angle is much larger than that found in Sc₂O@<i>T_d</i>(19151)-C₇₆ but almost comparable to that in Sc₂O@<i>C</i>_<i>s</i>(6)-C₈₂, suggesting that the endohedral Sc₂O unit is flexible and can display large variation in the Sc–O–Sc angle, which depends on the size and shape of the cage. Computational studies show that there is a formal transfer of four electrons from the Sc₂O unit to the C₈₀ cage, i.e., (Sc₂O)⁴⁺@(C₈₀)^4–, and the HOMO and LUMO are mainly localized on the C₈₀ framework. Moreover, thermal and entropic effects are seen to be relevant in the isomer selection. Comparative studies between the recently reported Sc₂C₂@C_2<i>v</i>(5)-C₈₀ and Sc₂O@<i>C</i>_2<i>v</i>(5)-C₈₀ reveal that, despite their close structural resemblance, subtle differences exist on the crystal structures, and the clusters exert notable impact on their spectroscopic properties as well as interactions between the clusters and corresponding cages