Exohedral Metallofullerenes

Huang and Freiser (132, 133) were able to prepare exohedral metal C60 ions [MC60]+ by direct reaction of the bare metal ions Fe+, Ni+, Co+, Cu+, Rh+, and La+ with Cgo vapor produced from a heated probe. The [MC60]+ ions when subjected to low-energy collision-induced dissociation with argon all produced the Cg0 ion. These results show that the metal ions attach to the outer surface of C60. The exohedral metallofullerene ions differ from the endohedral metallofullerenes produced by laser ablation of metal oxide-graphite mixtures and support the observations of Smalley and co-workers (148) who found that endohedral metallofullerene ions dissociate by loss of C2 units. 

Exohedral metallofullerenes have attracted attention concerning the effect of metal coordination on the chemical and physical properties of Ceo- It has been... 

The endohedral (metal trapped inside the carbon cage) nature of the metallofullerenes has been questioned, but gas phase photofragmentation experiments of ions99,100 and solid-state measurements indicate that the metals are endohedral not exohedral.101 Exohedral metallofullerenes have been prepared in the gas phase but they have different properties to the endohedral metallofullerenes prepared by the arc or laser methods.102-104 The symbol has been used to denote a species inside the fullerene cage and this symbol will be now used to denote endohedral metallofullerenes. 

Synthesis, structure, and properties of exohedral metallofullerenes MnC60 (M = transition metal) 00ZSK164. 

Chamberlain TW, Champness NR, Schroeder M, Khlobystov AN. A piggyback ride for transition metals encapsulation of exohedral metallofullerenes in carbon nanotubes. Chem Eur J 2011 17 668-74. S668/661-S668/665. 

It was shown how both endohedral and exohedral fullerenes can be inserted in nanotubes. In the peapods containing endohedral fullerenes (for instance Ce Cg2), HRTEM images showed interesting rotation and translation motion of the trapped spheroids. Exohedral metallofullerenes, CsC io have been synthesized and successfully encapsulated into SWCNTs via a new chemical reduction of Cgo molecules into anions. The addition of iodine to already prepared peapods allowed the coalescence of Cgo directly inside the nanotubes. Indeed, after heating at 550 C, iodine-doped peapods, inside the Cgo molecules molecules have been transformed in a tubular structure. Khlobystov et al. were able to perform reactions on the inner surface of carbon nanotubes in the presence of catalyti-cally active atoms of rhenium and monitor the whole process via HRTEM. ... 

The first exohedral metallofullerenes to be synthesized and isolated were if complexes of C6oPt(PPh3)2 and C6oPd(PPh3)2 [7-9]. This work was later extended to monoatomic coordination by a whole range of metals including Ti, Nb, Re, Fe, Ru and Ni, and also multiple metal doping [4, 10-13]. 

Two DFT methods, namely OLYP and B3LYP, have been compared via geometrical parameters and stability of various exohedral metallofullerene structures. 

Formation of equivalent bonds in metal-ligand bonding is referred to as hapticity (r ), and in the case of exohedral metallofullerenes, single atoms may in principle explore the range from one to six for r], depending on the site of coordination to the fullerene. To our knowledge, only r7 -substituted exohedral metallofullerenes have been observed so far and in the present work we focus on this coordination mode. 

Akasaka T, Nagase S, Kobayashi K, Suzuki T, Kato K, Yamamoto K, Funasaka H and Takahashi T 1995 Exohedral derivatization of an endohedral metallofullerene Gd Cg2 J. Chem. See., Chem. Commun. 1343-4... 

Since then, several studies on the chemical reactivity of endohedral metallofullerenes have been performed in order to understand their basic chemical properties. The endohedral metallofullerenes Gd C82 [137], La2 C80, and Sc2 C84 [138] showed similar behavior towards disilirane, forming the corresponding adducts via C-Si bonds. Also, similar functionalization of La C82 was achieved with digermirane [ 139,140]. However, when diphenyldiazomethane was added to La C82 an exohedral adduct was formed via C-C bonds [ 140,141 ]. This organic functionalization of endohedral metallofullerenes opened the way to chemically tune the electronic properties of the so-produced materials, the degree of charge transfer, and ultimately their electronic properties. 

Tagmatarchis N., Taninaka A., Shinohara H. (2002) Production and EPR characterization of exohedrally perfluoroalkylated paramagnetic lanthanum metallofullerenes (La C82)-(C8Fn)2. Chem. Phys.Lett. 355 226-232. 

The exohedral derivatives of fullerenes with organometallic compounds have received extensive attention and appropriate materials have been generated as catalysts, molecular devices, liquid crystals, and so on [10-13]. The discussion in this chapter will not address such materials but will only specifically examine endohedral metallofullerenes because they are viewed as more unique, fascinating, and promising due to the strong interactions between the encapsulated metallic species and the carbon cages [2]. 

Akasaka, T., Nagase, S., Kobayashi, K. etal. (1995) Exohedral derivatization of an endohedral metallofullerene Gd C82. Journal of the Chemical Society - Chemical Communications, 1343-1344. 

---