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

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• 作者：Taishan Wang ; Chunru Wang
• 刊名：Accounts of Chemical Research
• 出版年：2014
• 出版时间：February 18, 2014
• 年：2014
• 卷：47
• 期：2
• 页码：450-458
• 全文大小：464K
• ISSN：1520-4898

文摘

Fullerenes are carbon cages assembled from fused hexagons andpentagons that have closed networks and conjugated 蟺 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 (I_h) is the most stable fullerene molecule. However, another highly symmetrical fullerene, I_h-C₈₀, is extremely unstable. The reason for this difference is the open-shell electronic structure of I_h-C₈₀, which has a 4-fold degenerate HOMO occupied by only two electrons. Predictably, once the degenerate HOMO of I_h-C₈₀ accepts six more electrons, it forms a closed-shell electronic structure similar to I_h-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 I_h-C₈₀ fullerenes.
In this Account, we focus on the molecular structures and paramagnetic properties of spherical I_h-C₈₀ endohedral fullerenes encaging a variety of metal moieties, such as metal atoms (M_n), metal nitride (M₃N), metal carbide (M_nC₂), metal carbonitride (M₃CN), and metal oxides (M₄O_m). We introduce several types of endohedral metallofullerenes such as Sc₄C₂@I_h-C₈₀, which exhibits a Russian-doll-like structure, and Sc₃CN@I_h-C₈₀, which encapsulates a planar metal carbonitride cluster. In addition, we emphasize the paramagnetic properties of I_h-C₈₀-based metallofullerenes, such as Sc₃C₂@I_h-C₈₀, Y₂@C₇₉N, and M₃N@I_h-C₈₀, to show how those spin-active species can present a controllable paramagnetism. This Account highlights an inspiring molecular world within the spherical I_h-C₈₀ cages of various metallofullerenes.