Fullerene, endohedral

Tsuchiya T, Akasaka T, Nagase S (2010) New vistas in fullerene endohedrals functionalization with compounds from main group elements. Pure Appl Chem 82 505-521... 

Rare Earth Metals Trapped Inside Fullerenes - Endohedral Metallofullerenes (EMFs)... 

Since the discovery by Kratschmer and Huffman last year of a simple method for producing macroscopic quantities of Cjo, C70, and some of the higher empty fullerenes, we have searched for a means of extending this technique to fill the void and make macroscopic quantities of internally substituted fullerenes— endohedral fullerene complexes. We report below our first success in this search. It involves a simple revision to the laser-vaporization method originally used in 1985 just do it in an oven at 1200 C. 

Keywoids Fullerene, Endohedral MetallofuUerene, Transition Metals, Helium, [2 + 2 + 2] Ring Opening. 

Since their discovery, fullerenes and their derivatives have been the subject of very extensive research. One of the topics investigated intensively are the linear and nonlinear optical (NLO) properties, owing to a variety of possible applications. Here we review some of the recent work of our group in this area, which is concerned with the ab-initio calculation of molecular NLO properties of two different kinds of fullerene derivatives, a) substituted 1,2-dihydro fullerenes and b) fullerenes endohedrally doped with atoms or small molecules. Apart from the purely electronic response, we also focus on the vibrational contributions to the NLO response, that is, to the response of the nuclei to the external electric fields. 

Figure 34.1 Representative examples of [60]fullerene, endohedral fullerene, graphene and a single-walled carbon nanotube.

Fullerene Endohedral Complexes. The possibility of trapping atoms or molecules inside carbon frameworks is a very peculiar property of fullerenes. Today there is indeed strong evidence that metal atoms can actually be trapped inside fullerene cages. A nomenclature for this peculiar kind of compounds has been even suggested (M Cn) for a metal atom M located inside a C fullerene. 

Endohedral metal fullerenes can be detected in relatively small amounts in the mass spectra in the laser vaporization cluster beams (vide supra). However, macroscopic quantities of these compounds may be produced rather readily either by vaporization in a laser furnace apparatus or by arc-burning of a composite rod of graphite and the corresponding metal oxide. In Fig. 4.50, a mass spectrum which illustrates the formation of a series of fullerene endohedral yttrium complexes obtained by laser vaporization of a composite graphite/ Y2O3 rod at 1200 ""C is reproduced. Among these species there is also one, Y2 Cs2, which corresponds to the inclusion of a metal cluster in the fullerene ball. 

In this chapter we will show how quantum-chemical calculations can assist in studies of fullerenes. In particular, we will discuss prediction and elucidation of the molecular structures of the empty fullerenes, endohedral metallofullerenes, and selected fullerene derivatives. Taking into the account the huge amount of literature published on this subject, any review of the field is necessarily incomplete. We wffl not try to cover the whole field instead, we will focus on several representative examples. 

Metal-carbide clusters are relevant to the fonnation of both endohedral fullerenes and carbon nanotubes [1351. There also exists a class of apparently stable metal-carbide cluster ions, = Ti, V, Cr, Zr and Hf), called... 

Cagle D W, Kennel S J, Mirzadeh S, Alford J M and Wilson L J 1999 In vivo studies of fullerene-based materials using endohedral metallofullerene radiotraoers Proc. Natl Acad. Sc/. USA 96 5182-7... 

Teligmann R C, Krawez N, Lin S-H, Campbell E E B and Hertel I V 1996 Endohedral fullerene produotion Nature 382 407... 

Y2 Cg2 denotes two Y atoms inside a Cg2 fullerene [19], Thus far, only small quantities of endohedrally-doped fullerenes have been prepared and only limited investigations of endohedrally-doped crystalline materials have been reported but steady progress is being made both in synthesis and in properties measurements [20]. 

Golden MS, Pichler T, Rudolf P (2004) Charge Transfer and Bonding in Endohedral Fullerenes from High-Energy Spectroscopy 109 201-229 Goodin DB, see Contakes SM (2007) 123 177-203 Gorelesky SI, Lever ABP (2004) 107 77-114... 

The organic inclusion compound 2,4,6-tris-(4-bromophenoxy)-l,3,5-triazine was used to create an ordered arrangement of endohedral fullerenes in a crystalline host matrix <06CPL327>. 

One particularly striking aspect of endohedral fullerene complexes is the surprising ability of the carbon cage to contain highly reactive species such as atomic nitrogen.1801 N C6o (54) has been prepared... 

Y. Rubin, Organic Approaches to Endohedral Metallo-fullerenes Cracking Open or Zipping Up Carbon Shells , Chem. Eur. J. 1997, 3,1009-1016. 

Y. Rubin, Ring Opening Reactions of Fullerenes Designed Approaches to Endohedral Metal Complexes , Top. Curr. Chem. 1999,199, 67-91. 

In contrast to carbon, which forms structures derived from both sp2 and sp3 bonds, silicon is unable to form sp2 related structures. Since one out of four sp3 bonds of a given atom is pointing out of the cage, the most stable fullerene-like structure in this case is a network of connected cages. This kind of network is realized in alkali metal doped silicon clathrate (19), which were identified to have a connected fullerene-like structure (20). In these compounds, Si polyhe-dra of 12 five-fold rings and 2 or 4 more six-fold rings share faces, and form a network of hollow cage structures, which can accommodate endohedral metal atoms. Recently, the clathrate compound (Na,Ba), has been synthesized and demonstrated a transition into a superconductor at 4 K (21). The electronic structure of these compounds is drastically different from that of sp3 Si solid (22). 

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