Endohedral Fullerenes

Abstract

The recent state in endohedral fullerenes is reviewed in terms of both sides of the fullerene: the new carbon cages including non‐IPR (IPR, isolated pentagon rule) structures as well as new species encaged in the inner fullerene void. A general principle is valid nowadays and used in endohedral fullerene research: the stabilizing ability of the encaged structure for the fullerene cage architecture and that of the fullerene cage for the encaged species. Thus, the cage size ranges from C 66 , the first non‐IPR fullerene cage, to C 100 while the encaged species are extended up to five atomic clusters as for Sc 3 C 2 . The world of endohedral fullerenes was significantly enlarged within the past seven years by the cluster fullerenes containing structures like the M 3 N nitrides. This review is focused on the new development of this amazing world of carbon nanostructures since 1999, including new structures, properties, and potential applications of endohedral fullerenes as well as prospects.

An Improbable Monometallic Cluster Entrapped in a Popular Fullerene Cage: YCN@Cs(6)-C82

“…The molecular structure of YCN@C s (6)-C 82 is unambiguously determined by single crystal X-ray diffraction crystallography performed on a high-quality cocrystal of YCN@C 82 with Ni II (OEP) (OEP = octaethylporphyrin), which was obtained by diffusing a benzene solution of YCN@C 82 into a chloroform solution of Ni II (OEP)12345678921. The asymmetric unit cell of the cocrystal YCN@C 82 ·Ni II (OEP)·1.73C 6 H 6 ·1.27CHCl 3 contains an entire molecule of both YCN@C 82 and Ni II (OEP), while the cavities are filled with disordered solvent molecules.…”

“…This is dramatically different to the analogous C 82 -based mono-EMFs entrapping a trivalent Group-III metal M@C 82 (M = Sc, Y, La etc. ), which are typically ESR-active due to their open-shell electronic structures34567. Instead, divalent metal-based C 82 mono-EMFs, such as Yb@C 82 , Ca@C 82 , and Sm@C 82 , are usually ESR-silent owing to their closed-shell structures527.…”

“…Endohedral metallofullerenes (EMFs) thus formed have now been revealed to host a variety of species inside the carbon cage, including atoms, ions, or clusters2345678. EMFs exhibit unique electronic properties as a consequence of charge transfer and electrostatic interactions between the entrapped species and the carbon cage, enabling their potential applications in electronics and biomedicine and so on2345678. As the first and representative conventional EMFs, monometallofullerenes (mono-EMFs) had been extensively investigated in the early study of EMFs, and nowadays it has been commonly accepted that mono-EMFs always exist in the form of M@C 2n 12345.…”

“…EMFs exhibit unique electronic properties as a consequence of charge transfer and electrostatic interactions between the entrapped species and the carbon cage, enabling their potential applications in electronics and biomedicine and so on2345678. As the first and representative conventional EMFs, monometallofullerenes (mono-EMFs) had been extensively investigated in the early study of EMFs, and nowadays it has been commonly accepted that mono-EMFs always exist in the form of M@C 2n 12345. Among them, La@C 82 is the first stable monometallofullerenes isolated by Smalley et al in 19912, featuring a three-electron transfer from La to the C 82 cage123.…”

“…Among them, La@C 82 is the first stable monometallofullerenes isolated by Smalley et al in 19912, featuring a three-electron transfer from La to the C 82 cage123. Later on, a wealth of other mono-EMFs M@C 2n (M = Sc, Y, La-Lu, Ca, Mg) have been successfully isolated, featuring the transfer of two or three electrons from the entrapped metal ion to the carbon cage, which is sufficient for the mutual stabilization of the entrapped metal cation and carbon cage that are not even available in their empty form123456. Thus, it seems improbable to entrap a single metal cation in the form other than M@C 2n .…”