Metallofullerene Complexes

An important characteristic of these metallofullerene complexes is their unique electrochemical properties. The comparison between the reduction potential of these complexes with those of free C o gives an indication of the localization and delocalization of ffie added electrons. In some mono- [180] and trimetallic C o complexes the first reduction wave is slightly more negative than that of free C o (for example, for [Os3(CO)n(j -C6o)] 1/2 = —1-08 V, compared to 3/2 = —1.05 V for free Cgo) [181]. This is consistent with metal-to-Cco-back-donation, and provides a direct indication of charge transfer upon complex formation. 

Metallobisfiillerene complexes are predicted to have intercage electronic communication between Cfio cages. The CV of [Rh4(CO)5(dppm)2(CNCH2C6H5)(/ 3-tf-,tf-,tf--C(,(,)2] (63) exhibits six well-separated reversible, one-electron redox waves localized at ffie Cgo cages [178]. Each redox wave corresponds to sequential, pairwise addition of six electrons into ffie two Ceo centers to form eventually -Rhe-Qo - The large peak separations [( 3/2, 1/2 ) = 0-19 V, 

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Tsuchiya T, Sato K, Kurihara H, Wakahara T, Nakahodo T, Maeda Y, Akasaka T, Ohkubo K, Fukuzumi S, Kato T, Mizorogi N, Kobayashi K, Nagase S (2006) Host-guest complexation of endohedral metallofullerene with azacrown ether and its application. J. Am. Chem. Soc. 128 6699-6703. 

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. 

At present, it is still not known why the M C6o-type metallofullerenes behave quite differently from the conventional M C82 type fullerenes in terms, for example, of the solubility property. This may correlate to high reactivity of M C6o toward moisture and/or air M C6o can possibly form weak complexes to stabilize themselves only with pyridine or aniline through their nonbonding electrons. Another possible rationale is that the carbon cage structures of the M C6o so far produced somehow do not satisfy the IPR, which again leads to high chemical reactivity of the species. To fully imderstand "the M C6o mystery" future studies on structural and electronic properties of these elusive metallofullerenes are definitely needed. 

The metallofullerenes were purified by CS2 extraction and toluene HPLC elution. The dominant products identified for neptunium and americium were An C82. Two uranium-containing metallofullerenes were identified, U C82 and U2 C8o. Based upon comparison with the optical spectra of lanthanide analogs, it was suggested that the oxidation state in these complexes might best be regarded as +3. 

Tsuchiya, T., Sato, K., Kurihara, H. etal. (2006) Host-guest complexation of endohedral metallofullerene with azacrown edier and its pUcation. Journal of the American Chemical Society, 128, 6699-6703. 

Yang, S.F. and Yang, S.H. (2002) Preparation and film formation behavior of the supramolecular complex of the endohedral metallofullerene Dy C82 with calix[8]arene. Langmuir, 18, 8488-8495. 

However, the calculations described above, together with others that have recently appeared, indicate that non-olefinic metallofullerenes and metal-doped nanostructures are stable. Because the synthesis of these complexes is... 

In general, electrochemical studies of Cg2 have been devoted to the study of its endohe-dral metallo complexes, in which metal atoms are trapped inside the fullerene cage. Part of the fascination with these molecules stems from two aspects of their electronic structures (1) Unlike noble gas endofullerenes, metallofullerenes are formed from a stable ion-pair association between a fulleride anion of charge n and a cation of charge n, which cannot escape from the anionic cage nor react with other substances outside the... 

The solids produced by the arc method are often complex mixtures of fullerenes and metallofullerenes and an important part of this chemistry has involved the purification of the individual metallofullerenes and even isomers of a particular species. In general a two-stage HPLC method has been used to separate the metallofullerenes from the empty fullerenes and purify individual metallofullerenes.105,106... 

Tml2, and that of other isolated uncommon divalent complexes there are also two endohedral metallofullerenes Sc Cg4 (Takahashi et al., 1995) and Tm C82 (Kirbach and Dunsch, 1996 Pichler et al., 1997) for which spectroscopic evidence points to the divalent nature of Sc and Tm, respectively they are worth mentioning here but they will not be discussed further. We will also consider the important issue of chemical systems in which uncommon divalent species may be present or have been postulated as intermediates, or displaying divalent-like reactivity. We will also report on the few low-valent scandium species that have been reported and finally on the zero-valent compounds. 

The electropolymerization method of functional monomers has proved successful in many cases, in particular to incorporate various ligands and their metallic complexes, like salen [66,245], porphyrin [246], diphosphine [247], pyridine [71,80,248,249], crown ether [250,251], metallofullerene [252], tetraazacyclotetradecane [253], or Prussian blue type [254] in a conjugated organic material like PPy, PTh, or PANE Thick films are likely to be obtained provided that the polymer is redox active at the deposition potential due to this, Zotti et al. demonstrated that 5,5 -bis(3,4-(ethylenedioxy)thien-2-yl)-2,2 -bipyridine could be electropolymerized when complexed by iron and ruthenium, but not in the case of complexation by nickel or copper [71]. 

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