Stable Metallofullerene Research Articles

Kinetic Stability of Non-IPR Fullerene Molecular Ions.

Many fullerenes that violate the isolated pentagon rule (IPR) form stable metallofullerenes. In general, a fullerene cage is kinetically stabilized by acquiring a given number of electrons. Kinetic stability of negatively charged non-IPR fullerenes, including the recently isolated endohedral metallofullerene with a heptagonal face, was rationalized in terms of bond resonance energy (BRE). Interestingly, molecular anions of conventional fullerenes found in most isolated metallofullerenes are kinetically stable with large positive BREs for all CC bonds. As we pointed out in 1993, the IPR does not apply to charged fullerenes because π-bonds shared by two five-membered rings are aromatized to varying extents.

Structures, stabilities, aromaticity, and electronic properties of C66 fullerene isomers, anions (C66 2−, C66 4−, C66 6−), and metallofullerenes (Sc2@C66)

Among all the 4478 classical isomers of C66, C66(C s :0060) with the lowest number of pentagon–pentagon fusions was predicted to be the most stable isomer, followed by isomers C66(C 2v :0011) and C66(C 2:0083). The infrared spectra and aromaticity of the most stable isomers were predicted. The relative stabilities of C66 isomers change with charges or doping of metals. The structures and relative stabilities of the most stable metallofullerenes were delineated and compared with experiment. Sc2@C66(C 2:0083) was predicted to be the most stable metallofullerene, although Sc2@C66(C 2v :0011) was observed. Charge-transfer from Sc2 to the fused pentagons and the bonding between these two moieties significantly decrease the strain energies caused by the pair of fused pentagons thereby stabilizing the fullerene cage.

Synthesis and in vivo study of metallofullerene based MRI contrast agent

Gd@C82(OH)40 has been developed as a new generation of MRI contrast agent. But recently, it was found that Gd@C82(OH)x with a larger number of OH (x>36) would lead to cage break and hence, release of highly toxic Gd ions. We synthesized the more stable Gd@C82(OH)x with less OH-number, Gd@C82(OH)16, and studied its proton relaxivity and MRI images. The results indicate that Gd@C82(OH)16 also gives high proton relaxivity, even higher than that of (NMG)2-Gd-DTPA. The bio-distribution indicated that Gd@C82(OH)16 tends to be entrapped in the liver and kidney and remained in tissue for about 2 hours. The results suggest that the more stable metallofullerene derivative Gd@C82(OH)16 can be the potential candidate of the new MRI contrast agent.

Investigation on the Electrochemistry of Gd @ C 82 / DDAB Films in an Aqueous Solution

Electrochemistry of films made from cationic surfactant didodecyldimethylammonium bromide (DDAB) containing metallofullerene on a glassy carbon electrode was investigated in an aqueous solution, and both oxidation and reduction peaks of films were found in the potential range between 0.6 and vs. a saturated calomel electrode. Electrochemically stable metallofullerene modified electrodes were produced. Furthermore, electrocatalysis of myoglobin and cytochrome c at the films was also studied. © 2004 The Electrochemical Society. All rights reserved.

Formation of polymer complexes of transition metals with fullerene

This paper reports on the results of ab initio unrestricted Hartree-Fock (UHF) calculations of the equilibrium geometry and binding energy for the transition-metal complexes Me(C5H5)2 and Me(C6H6)2 and the energetically stable metallofullerene complexes Me(C60)2, where Me=Ti, V, Cr, Fe, and Ni. The calculation technique is worked out using the ferrocene molecule. The calculated geometry and binding energy agree satisfactorily with the experimental data.

A C82 Carbon Cage Stable toward Two Different Oxidation States of Endohedral Metal Atoms

The effect of transmutation of a metallic element encaged in C{sub 82} through EC radioactive decay was studied for the {sup 146}Gd {r_arrow} {sup 146}Eu {r_arrow} {sup 146}Sm decay series. The metallofullerene containing the EC decay progeny {sup 146}Eu was found chemically stable and eluted in a HPLC separation at a retention time which corresponded to the retention time of one of the minor isomers of Eu {at} C{sub 82}. As the oxidation state of the metal atom in Gd {at} C{sub 82} and Eu {at} C{sub 82} is known to be +3 and +2, this result suggests that the C{sub 82} cage which forms a chemically stable metallofullerene with the metal atom at the +3 oxidation state can also form a stable metallofullerene with a metal atom at the +2 oxidation state.

Specificity of carbon cages towards oxidation states of metal atoms in metallofullerenes

The effect of transmutation of the metallic element encaged in C 82 through β − radioactive decay has been studied for two decay series of 155 Sm→ 155 Eu and 177 Yb→ 177 Lu , and the results were examined in combination with those reported for the decay series of 161 Gd→ 161 Tb . The metallofullerenes containing the β − decay progeny element are chemically stable if its oxidation state remains the same as that of the parent atom, namely, (+3→+3) and (+2→+2), whereas they become unstable if the oxidation state is changed like (+2→+3). This suggests that specific carbon cages can form stable metallofullerenes only with a metal atom of a given oxidation state: carbon cages for metal atoms of +2 oxidation are not the stable cage for atoms of the +3 oxidation state.

Isolation and Characterization of an ESR-Active La@C82 Isomer

A minor isomer of LaC[sub 82] has been isolated with an efficient HPLC method. The isolated minor LaC[sub 82] was well identified as a stable metallofullerene molecule. Both mass and ESR spectra confirmed that it was LaC[sub 82] with a 0.836-G [sup 139]La hyperfine splitting. Visible and near-IR absorption spectra, cyclic and differential pulse voltammograms, and [sup 13]C hyperfine splitting structures in an ESR spectrum for the sample showed features quite different from those for the major isomer of LaC[sub 82] with a 1.159-G [sup 139]La hyperfine splitting. We concluded that isolated species is a carbon-cage isomer of the major LaC[sub 82]. 12 refs., 4 figs.

Formation and stability of small metallocarbon clusters: what is the specificity for the formation of stable metallofullerenes?

To clarify the specificity for the formation of stable metallofullerenes M@C 82, laser vaporization time-of-flight mass spectroscopy was applied to metal—carbon composite rods, which have been used to produce extractable metallofullerenes. Most of the metal elements in the fourth row of the periodic table (K to Zn), the group IIIA elements (La, Y, and Sc), and some of the lanthanides (Ce, Sm, Eu, Gd, Tb, and Lu) were examined. The results of mass spectra taken by three different modes (positive, negative, and post-ionization) were shown and compared with the laser desorption time-of-flight mass spectra of the metallofullerene-containing crude extract for each element. It was shown that there was a strong correlation between the formation of MC n ( n>4) and the formation of MC 82. Also, a preliminary ab initio calculation was performed, using MC 6 (M = Sc, Y, and K) as typical examples, in order to elucidate the stability and the molecular structure of MC n . It was shown that there was a difference in the binding energy and the optimized molecular structure between the cases of M = Sc, Y, and M = K. All of the above findings strongly support the view that MC n ( n>4) has an important role in the formation process of M@C 82.

Isolation and Characterization of Two Esr–Active La@C82 Isomers

ABSTRACTTwo abundant ESR-active lantanofullerene species have been isolated with an efficient HPLC method. Each of isolated species was well identified as a stable metallofullerene molecule. Both mass and ET 9 spectra confirmed that they were La@C82 with 1.159-G and 0.836-G 139La hyperfine splittings. Visible and near-IR absorption spectra, cyclic and differential pulse voltammograms, and 13 C hyperfine splitting structures in ESR spectra for the samples showed features quite different from each other. Their differences were discussed on the basis of their structures.

How to fill or empty a graphitic onion

We present the preparation of metal enclosed clusters using an arc-discharge experiment. Gold clusters can be encapsulated in carbon onions, even if Au atoms have not yet been found to form metallo-fullerenes. We have subjected the sample to an intense electron beam, and in the case of encapsulated gold clusters, we have observed a tendency to migrate out of the concentric graphitic cages, which close again afterwards. These observations suggest the plausibility of a similar mechanism based on opening and closing of the fullerene cage, whether for the growth of stable metallo-fullerenes or for the decomposition of instable ones.