Endohedral filling

Figure 3.9 (a) The nondeltahedral endohedrally filled anion [Co Ceio] [81] (b) The largest... 

Due to the nanoscale confinement in the system, the interaction via interfacial bonding is considered to play an essential role in the impacts. Morphologically, the interfacial interaction sites on the CNT surface are (a) defeet sites at the tube ends and side-walls (b) covalent side-wall bindings (c) non-eovalent exohedral side-wall bindings and (d) endohedral filling (Figure 1.6). Three routes have been commonly used for preparation of... 

Edelmann F T 1995 Filled buckyballs—recent developments from the endohedral metallofullerenes of lanthanides Angew. Chem. Int. Edn. Engl. 34 981-5... 

The chemical modification of CNTs can be endohedral (inside the cavity of the tube) or exohedral [42]. There are some examples in the literature that have demonstrated the filling of CNTs with fullerenes, biomolecules (proteins, DNA), metals and oxides that have been driven inside by capillary pressure [39, 42, 72-78]. However, in this section we will focus on exohedral functionalization, taking place just at the external walls of the tubes. Both covalent (chemical-bond formation) and noncovalent (physiadsorption) functionlizations can be carried out. In the following... 

Table 14.3 Calculated endohedral He chemical shifts and symmetry of He C2o, He C6o and He Cgo species with different filling degree of the k electron system [107],...

The carbon arc is a versatile method to generate a wide variety of nanostruct-ured carbon materials such as fullerenes (7,11), endohedral metallofullerenes (12-14), nanotubes (6,8-10,15), nanocapsules filled with metals (or carbides) (16-18), and so forth. Arc discharge is characterized by the high electric current... 

This review describes the preparation, characterization, and properties of all nonpolymeric complexes that contain a metal removed from the fullerene also are included. The article does not cover the essentially ionic fullerides MmC (4) or the endohedral metallofullerenes MmC (8), which have been reviewed previously. The extended fullerenes, or so-called carbon nanotubes, which have hollow centers and can be filled with metal salts, also are not discussed. The majority of complexes involve 7r-bonds and, apart from alkyl lithium fullerides, the potentially useful synthetic area of o- complexes has not been explored. Table I shows the occurrence of metal-bound adducts across the periodic table. 

Typically, endohedral metallofullerenes are produced in an electric arc by evaporating composite carbon rods filled with atomic or molecular elements that later end up inside the carbon cages. However, the yield of endohedral metallofullerenes is rather low, less than 1%, and their formation mechanism is unknown. Furthermore, no particular rules are applied on the selection of the carbon cage that will be formed and on the nature of the element that ultimately will be encapsulated. 

Endohedral functionalization of CNTs is the filling of the tubes with various atoms or small molecules [254]. The internal cavity of CNTs (1-2 nm in diameter) provides space for the accommodation of guest molecules [254-260], Even small proteins and other biomolecules [207, 208, 261] and oligonucleotides [262] have been trapped in the nanotube cavity. In 1998, Luzzi s group [263] for the first... 

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. 

As seen before, the inside of the fullerene cages is empty, so it is self-suggesting to try to fill this cavity with atoms or molecules. Indeed the isolation of so-called endohedral fullerenes succeeded quite soon after the discovery of fullerenes themselves. In endohedral species, single or even several atoms are situated inside the carbon cage, so it is purely topological circumstances that prevent them from breaking out of these compounds. 

A first principles DFT investigation of the electronic structure of potassium doped C ) was carried out by Saito and Oshiyama [60]. Three different positions of the potassium atom were considered the endohedral center of C 0 and the tetrahedral and octahedral interstitial sites. The most stable position has been predicted for the tetrahedral site with a cohesion energy of 10 eV, followed by the octahedral site ( 8 eV) and the center of the fullerene molecule ( 6 eV). It was revealed that, in all cases, the 4s electron of the K transfers to the LUMO level of C60. Thus, in the frc.c. A3C60 phase three valence electrons of alkaline metals transfer to the lowest unoccupied level of each fullerene molecule and form the half filled conductivity band. In the case of b.c.c. AeCeo, the tiu electronic level of fullerene is completely filled by electrons, and the material is not conductive. 

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