Endohedral Metallofullerenes Based on Spherical I_h-C₈₀ Cage: Molecular Structures and Paramagnetic Properties

Abstract

Fullerenes are carbon cages assembled from fused hexagons andpentagons that have closed networks and conjugated π systems. The curve of the fullerene structure requires that the constituent carbon atoms take on a pyramidal shape and produces extra strain energy. However, the highly symmetrical geometry of the fullerene decreases the surface tension in these structures, so highly symmetrical fullerenes are usually very stable. For example, C60 with icosahedral symmetry (Ih) is the most stable fullerene molecule. However, another highly symmetrical fullerene, Ih-C80, is extremely unstable. The reason for this difference is the open-shell electronic structure of Ih-C80, which has a 4-fold degenerate HOMO occupied by only two electrons. Predictably, once the degenerate HOMO of Ih-C80 accepts six more electrons, it forms a closed-shell electronic structure similar to Ih-C60 and with comparable stability. Because the hollow structure of fullerenes can encapsulate metal atoms and those internal metals can transfer electrons to the fullerene cage, the encapsulation of metal clusters may provide an ideal technique for the stabilization of the Ih-C80 fullerenes. In this Account, we focus on the molecular structures and paramagnetic properties of spherical Ih-C80 endohedral fullerenes encaging a variety of metal moieties, such as metal atoms (Mn), metal nitride (M3N), metal carbide (MnC2), metal carbonitride (M3CN), and metal oxides (M4Om). We introduce several types of endohedral metallofullerenes such as Sc4C2@Ih-C80, which exhibits a Russian-doll-like structure, and Sc3CN@Ih-C80, which encapsulates a planar metal carbonitride cluster. In addition, we emphasize the paramagnetic properties of Ih-C80-based metallofullerenes, such as Sc3C2@Ih-C80, Y2@C79N, and M3N@Ih-C80, to show how those spin-active species can present a controllable paramagnetism. This Account highlights an inspiring molecular world within the spherical Ih-C80 cages of various metallofullerenes.

An atlas of endohedral Sc2S cluster fullerenes

“…To date, more than two hundred EMFs have been characterized, including mono-metallofullerenes, dimetallofullerenes, trimetallofullerenes, and fullerenes incorporating clusters various kinds [4]. Amongst the EMFs, those in which the encapsuland is a metallic cluster have attracted attention because of their novel geometries and properties [5,6]. However, as far as we are aware, the mechanism of formation of EMFs has not yet been clarified, even though so many EMFs have been reported.…”

Sc2O@Td(19151)‐C76: Hindered Cluster Motion inside a Tetrahedral Carbon Cage Probed by Crystallographic and Computational Studies

“…[5][6][7][8][9] Since the discovery of Sc 3 N@C 80 in 1999, [10] cluster fullerenes (CFs) have been of particular interest in the field of endohedral fullerenes as ar esult of their exceptionally high yield and excellent stabilitya nd the unique structural variety of both clusters and cages, which resultsi nt heir tunable physical and chemical properties. [11][12][13][14] To date,avariety of cluster fullerenes have been reported, including nitride (NCFs), [15][16][17] carbide( CCFs), [18,19] hydrocarbide (HCCFs), [20] oxide (OCFs), [21,22] sulfide( SCFs), [23][24][25] carbonnitride (CNCFs), [26,27] and di/trimetallic clusterf ullerenes. [28,29] In particular,t he OCF family has demonstratede xceptional structuralv ersatility of the encapsulated oxide clusters, whichh ave includedS c 2 O, [21] Sc 4 O 2 , [22] and Sc 4 O 3 [30] structures.I ncontrast, the reported cage structures of this family have been limited to I h (7)-C 80 , C s (6)-C 82 ,a nd the very recent C 2 (7892)-C 70 cages.…”

Sc2O@C2v(5)-C80: Dimetallic Oxide Cluster Inside a C80 Fullerene Cage

“…9 For example, isomeric cages of C 80 are popular cages for various forms of endohedral fullerenes. 21 However, one of them, C 2v (5)-C 80 , remained missing until its recent discovery by Akasaka et al in the study of Sc 2 C 2 @ C 2v (5)-C 80 . 22 It was found that this cage structure was stabilized by a four-electron-transfer from the encapsulated Sc 2 C 2 cluster.…”