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

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

Sc₂O@<i>C</i>_3<i>v</i>(8)‑C₈₂: A Missing Isomer of Sc₂O@C₈₂

By introducing CO₂ as the oxygen source during the arcing process, a new isomer of Sc₂O@C₈₂, Sc₂O@<i>C</i>_3<i>v</i>(8)-C₈₂, previously investigated only by computational studies, was discovered and characterized by mass spectrometry, UV–vis–NIR absorption spectroscopy, cyclic voltammetry, ⁴⁵Sc NMR, density functional theory (DFT) calculations, and single-crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the cage symmetry was assigned to <i>C</i>_3<i>v</i>(8) and suggests that Sc₂O cluster is disordered inside the cage. The comparative studies of crystallographic data further reveal that the Sc1–O–Sc2 angle is in the range of 131.0–148.9°, much larger than that of the Sc₂S@<i>C</i>_3<i>v</i>(8)-C₈₂, demonstrating a significant flexibility of dimetallic clusters inside the cages. The electrochemical studies show that the electrochemical gap of Sc₂O@<i>C</i>_3<i>v</i>(8)-C₈₂ is 1.71 eV, the largest among those of the oxide cluster fullerenes (OCFs) reported so far, well correlated with its rich abundance in the reaction mixture of OCF synthesis. Moreover, the comparative electrochemical studies suggest that both the dimetallic clusters and the cage structures have major influences on the electronic structures of the cluster fullerenes. Computational studies show that the cluster can rotate and change the Sc–O–Sc angle easily at rather low temperature

Isomeric Sc₂O@C₇₈ Related by a Single-Step Stone–Wales Transformation: Key Links in an Unprecedented Fullerene Formation Pathway

It has been proposed that the fullerene formation mechanism involves either a top-down or bottom-up pathway. Despite different starting points, both mechanisms approve that particular fullerenes or metallofullerenes are formed through a consecutive stepwise process involving Stone–Wales transformations (SWTs) and C₂ losses or additions. However, the formation pathway has seldomly been defined at the atomic level due to the missing-link fullerenes. Herein, we present the isolation and crystallographic characterization of two isomeric clusterfullerenes Sc₂O@<i>C</i>_2<i>v</i><i>(3)</i>-C₇₈ and Sc₂O@<i>D</i>_3<i>h</i><i>(5)</i>-C₇₈, which are closely related via a single-step Stone–Wales (SW) transformation. More importantly, these novel Sc₂O@C₇₈ isomers represent the key links in a well-defined formation pathway for the majority of solvent-extractable clusterfullerenes Sc₂O@C_2<i>n</i> (<i>n</i> = 38–41), providing molecular structural evidence for the less confirmed fullerene formation mechanism. Furthermore, DFT calculations reveal a SWT with a notably low activation barrier for these Sc₂O@C₇₈ isomers, which may rationalize the established fullerene formation pathway. Additional characterizations demonstrate that these Sc₂O@C₇₈ isomers feature different energy bandgaps and electrochemical behaviors, indicating the impact of SW defects on the energetic and electrochemical characteristics of metallofullerenes

Facile Synthesis of an Extensive Family of Sc₂O@C_2<i>n</i> (<i>n</i> = 35–47) and Chemical Insight into the Smallest Member of Sc₂O@<i>C</i>₂(7892)–C₇₀

An extensive family of oxide cluster fullerenes (OCFs) Sc₂O@C_2<i>n</i> (<i>n</i> = 35–47) has been facilely produced for the first time by introducing CO₂ as the oxygen source. Among this family, Sc₂O@C₇₀ was identified as the smallest OCF and therefore isolated and characterized by mass spectrometry, ⁴⁵Sc nuclear magnetic resonance, UV–vis–near-infrared absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The combined experimental and computational studies reveal a non-isolated pentagon rule isomer Sc₂O@C₂(7892)–C₇₀ with reversible oxidative behavior and lower bandgap relative to that of Sc₂S@<i>C</i>₂(7892)–C₇₀, demonstrating a typical example of unexplored OCF and underlining its cluster-dependent electronic properties