La₃N@C₉₂: An Endohedral Metallofullerene Governed by Kinetic Factors?

Different structures have been proposed so far for the C₉₂ isomer that encapsulates M₃N (M = La, Ce, Pr). We show here that the electrochemical properties of the predicted most abundant (thermodynamic) isomer for La₃N@C₉₂ does not agree with experiment. After a systematic search within the huge number of possible C₉₂ isomers, we propose other candidates with larger electrochemical gaps for La₃N@C₉₂ before its structure could be finally determined by X-ray crystallography. We do not discard that the thermodynamic isomer could be detected in future experiments though

Sc₃O@<i>I</i>_h(7)‑C₈₀: A Trimetallic Oxide Clusterfullerene Abundant in the Raw Soot

The trimetallic oxide clusterfullerene (OCF) Sc₃O@C₈₀ has been obtained with rather high abundance in the raw soot. Most of the formed product, however, remained nonextracted in the soot so that only a small amount of it was isolated and purified. The tiny quantity of pure product acquired made only possible characterization by UV–vis-NIR spectroscopy. DFT computations predict Sc₃O@<i>I</i>_h(7)-C₈₀ to be the isolated isomer and provide further information about the electronic structure and other (magnetic and electrochemical) properties of this singular OCF. Significant spin density on the endohedral Sc ions and in cavea redox processes are two main features of Sc₃O@<i>I</i>_h(7)-C₈₀, which is isoelectronic to the anion of the prototypical nitride Sc₃N@<i>I</i>_h(7)-C₈₀. Polymerization is predicted to be a favored process that could explain the very low yields obtained once the product is purified

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

Capturing the Fused-Pentagon C₇₄ by Stepwise Chlorination

As a bridge to connect medium-sized fullerenes, fused-pentagon C₇₄ is still missing heretofore. Of 14 246 possible isomers, the first fused-pentagon C₇₄ with the Fowler–Manolopoulos code of 14 049 was stabilized as C₇₄Cl₁₀ in the chlorine-involving carbon arc. The structure of C₇₄Cl₁₀ was identified by X-ray crystallography. The stabilization of pristine fused-pentagon C₇₄ by stepwise chlorination was clarified in both theoretical simulation with density functional theory calculations and experimental fragmentation with multistage mass spectrometry

Capturing the Fused-Pentagon C₇₄ by Stepwise Chlorination

As a bridge to connect medium-sized fullerenes, fused-pentagon C₇₄ is still missing heretofore. Of 14 246 possible isomers, the first fused-pentagon C₇₄ with the Fowler–Manolopoulos code of 14 049 was stabilized as C₇₄Cl₁₀ in the chlorine-involving carbon arc. The structure of C₇₄Cl₁₀ was identified by X-ray crystallography. The stabilization of pristine fused-pentagon C₇₄ by stepwise chlorination was clarified in both theoretical simulation with density functional theory calculations and experimental fragmentation with multistage mass spectrometry

Zigzag Sc₂C₂ Carbide Cluster inside a [88]Fullerene Cage with One Heptagon, Sc₂C₂@<i>C</i>_<i>s</i>(hept)‑C₈₈: A Kinetically Trapped Fullerene Formed by C₂ Insertion?

A non-isolated pentagon rule metallic carbide clusterfullerene containing a heptagonal ring, Sc₂C₂@<i>C</i>_<i>s</i>(hept)-C₈₈, was isolated from the raw soot obtained by electric arc vaporization of graphite rods packed with Sc₂O₃ and graphite powder under a helium atmosphere. The Sc₂C₂@<i>C</i>_<i>s</i>(hept)-C₈₈ was purified by multistage high-performance liquid chromatography (HPLC), cocrystallized with Ni–(octaethylporphyrin), and characterized by single-crystal X-ray diffraction. The diffraction data revealed a zigzag Sc₂C₂ unit inside an unprecedented <i>C</i>_<i>s</i>(hept)-C₈₈ carbon cage containing 13 pentagons, 32 hexagons, and 1 heptagon. Calculations suggest that the observed nonclassical fullerene could be a kinetically trapped species derived from the recently reported Sc₂C₂@<i>C</i>_2<i>v</i>(9)-C₈₆ via a direct C₂ insertion

Formation of Curvature Subunit of Carbon in Combustion

Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C₅–C₁₈ that are online produced in the flame of acetylene–cyclopentadiene–oxygen and in situ captured by C₆₀ or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C₂₀H₁₀. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process

Formation of Curvature Subunit of Carbon in Combustion

Curvature prevalently exists in the world of carbon materials (e.g., fullerenes, buckyl bowls, carbon nanotubes, and onions), but traditional C2-addition mechanisms fail to elucidate the mechanism responsible for the formation of carbon curvature starting from a pentagonal carbon ring in currently available chemical-physical processes such as combustion. Here, we show a complete series of nascent pentagon-incorporating C₅–C₁₈ that are online produced in the flame of acetylene–cyclopentadiene–oxygen and in situ captured by C₆₀ or trapped as polycyclic aromatic hydrocarbons for clarifying the growth of the curved subunit of C₂₀H₁₀. A mechanism regarding C1-substitution and C2-addition has been proposed for understanding the formation of curvature in carbon materials, as exemplified by the typical curved molecule containing a single pentagon completely surrounded by five hexagons. The present mechanism, supported by the intermediates characterized by X-ray crystallography as well as NMR, has been experimentally validated for the rational synthesis of curved molecule in the commercially useful combustion process