Fullerene isolation

The biggest fullerene isolated and studied using electrochemistry is C92, which shows eight reversible reductions and one broad irreversible oxidation. The intensities of the eight reduction peaks can be grouped into two distinct sets, thus indicating that the electrochemistry corresponds to a mixture of two isomers The reduction and oxidation potentials are shown in Table 8.1. 

The geometrical parameters of equilibrium configurations of small fullerenes isolated molecules C , their dimers (Cn)2 and cuban-like clusters(Cn)8 are obtained for n = 20, 24, 28, 32. The Cuban like clusters can be considered as fragments of polymerized crystal structures with simple cubic symmetry. Total energy, heat of formation, energies of HOMO and LUMO orbitals, density of one-electron states (DOS) are determined for equilibrium configurations of all these objects. All the computations are performed by help of pocket PC Gamess in frames of optimized semi-empirical PM3-basis [4-5],... 

Austin, S. J., Fowler, P. W., Orlandi, G., Manolopou-los, D. E., Zerbetto, F. (1994). Relative stabilities of Cjs isomers - a numerical test of the fullerene isolated-pentagon rule. Chemical Physics Letters, 226(1-2), 219-225. 

In addition to the most abundant fullerene, namely [60]fullerene, a number of higher fullerenes have also been isolated and characterized, including [70] (point group D . ), chiral [76] (point group Dj), the D and Cj isomers... 

Taylor R, Hare J P, Abdul-Sada A K and Kroto H W 1990 Isolation, separation and oharaoterization of the fullerenes Cgg and C g, the 3rd form of oarbon J. Chem. Soc., Chem. Commun. 1423-5... 

Diederich F, Whetten R L, Thilgen C, EttI R, Chao I and Alvarez M M 1991 Fullerene isomerism—isolation of C2y-... 

Fullerenes are described in detail in Chapter 2 and therefore only a brief outline of their structure is presented here to provide a comparison with the other forms of carbon. The C o molecule, Buckminsterfullerene, was discovered in the mass spectrum of laser-ablated graphite in 1985 [37] and crystals of C o were fust isolated from soot formed from graphite arc electrodes in 1990 [38]. Although these events are relatively recent, the C o molecule has become one of the most widely-recognised molecular structures in science and in 1996 the codiscoverers Curl, Kroto and Smalley were awarded the Nobel prize for chemistry. Part of the appeal of this molecule lies in its beautiful icosahedral symmetry - a truncated icosahedron, or a molecular soccer ball, Fig. 4A. 

In the synthesis of Ceo, larger molecular weight fullerenes C (n > 60) are also formed, by far the most abundant being C70. However, sufficient quantities of C76, C78, and Cs4 have also been isolated to be studied in some detail. 

At higher frequencies (above 200 cm ) the vibrational spectra for fullerenes and their cry.stalline solids are dominated by the intramolecular modes. Because of the high symmetry of the Cgo molecule (icosahedral point group Ih), there are only 46 distinct molecular mode frequencies corresponding to the 180 6 = 174 degrees of freedom for the isolated Cgo molecule, and of these only 4 are infrared-active (all with Ti symmetry) and 10 are Raman-active (2 with Ag symmetry and 8 with Hg symmetry). The remaining 32 eigcnfrequencies correspond to silent modes, i.e., they are not optically active in first order. 

Although laser-ablation method with pure carbon as the target only gives fullerenes, SWCNT can be obtained at high yield by mixing Co-Ni into the target carbon [16]. Isolation of thus synthesized SWCNT is rather of ease since the crude product is almost free of nanoparticle and amorphous carbon [39]. Such... 

Confirming its structure required isolating enough Cgo to apply modern techniques of structure determination. A quantum leap in fullerene research came in 1990 when a team led by Wolfgang Kratschmer of the Max Planck Institute for Nuclear Physics in Heidelberg and Donald Huffman of the University of Arizona successfully prepared buckmin-sterfullerene in amounts sufficient for its isolation, purification, and detailed study. Not only was the buckminsterfullerene structure shown to be correct. 

The tremendous burst of excitement which attended the initial isolation in 1990 of weighable amounts of separated fullerenes has been followed by an unparalleled and sustained surge of activity as chemists throughout the world rushed to investigate the chemical reactivity of these novel molecular forms of carbon. 

Kuhn s carbanion analogues, [44 ], [45 ] and [46 ], have recently been synthesized, and the precursor hydrocarbons [44]-H, [45]-H and [46J-H dissociate into the respective anions in DMSO to show deep blue colours without any added base (Kinoshita et al., 1994). A fullerene anion, Bu Qb [47 ], has also been obtained as a stable carbanion (Fagan et al., 1992) its lithium salt has been isolated in the form Li [47 ]-4MeCN or Li [47"]-3-4THF. Several stable all-hydrocarbon anions of precursor hydrocarbons with low pKa values ( 7) are listed in Table 2, along with their oxidation potentials, ox-... 

The ability of a dendritic shell to encapsulate a functional core moiety and to create a specific site-isolated microenvironment capable of affecting the molecular properties has been intensively explored in recent years [19]. A variety of experimental techniques have been employed to evidence the shielding of the core moiety and to ascertain the effect of the dendritic shell [19, 20]. Dendrimers with a fullerene core appear to be appealing candidates to evidence such effects resulting from the presence of the surrounding dendritic branches. Effectively, the lifetime of the first triplet excited state of fullerene derivatives... 

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