Showing papers on "Fullerene published in 1993"
TL;DR: Application of the wr-orbital axis vector theory to the geometries of structurally characterized organometallic derivatives of C60 and C70 shows that the reactivity exhibited by the fullerenes may be attributed to the relief of a combination of local and global strain energy.
Abstract: Within the wr-orbital axis vector theory, the total rehybridization required for closure of the fullerenes is approximately conserved. This result allows the development of a structure-based index of strain in the fullerenes, and it is estimated that about 80 percent of the heat of formation of the carbon atoms in C60 may be attributed to a combination of v strain and steric inhibition of resonance. Application of this analysis to the geometries of structurally characterized organometallic derivatives of C60 and C70 shows that the reactivity exhibited by the fullerenes may be attributed to the relief of a combination of local and global strain energy. C60 is of ambiguous aromatic character with anomalous magnetic properties but with the reactivity of a continuous aromatic molecule, moderated only by the tremendous strain inherent in the spheroidal structure.
822 citations
TL;DR: Cyclopropylation of Fullerenes C60 and C70 is achieved by a tandem process followed by intramolecular substitution of the halogen yields fullerene derivatives with functional groups.
Abstract: Cyclopropylation of Fullerenes
Cyclopropylation of fullerenes C60 and C70 is achieved by a tandem process. Michael addition of a stabilized α-halocarbanion to fullerenes followed by intramolecular substitution of the halogen yields fullerene derivatives with functional groups.
805 citations
TL;DR: In this article, a method to grow carbon microtubules with fullerene structure (buckytubes) has been identified, which consists of the catalytic decomposition of acetylene over iron particles at 700 °C.
Abstract: A method to grow carbon microtubules with fullerene structure (buckytubes) has been identified. The method consists of the catalytic decomposition of acetylene over iron particles at 700 °C. Carbon microtubules of up to 50 μm in length are synthesized by this method. Electron diffraction and high resolution electron microscopy studies demonstrate that the structure of these microtubules corresponds to the helical structure recently reported by S. Iijima, Nature 354, 56(1991), prepared using an arc‐discharge evaporation method.
672 citations
661 citations
IBM1
TL;DR: The existence of such species is now strongly supported by a growing body of experimental evidence as discussed by the authors, and their structure and properties are beginning to be explored in milligram quantities, and their structures and properties have been explored.
Abstract: Encapsulating atoms or molecules inside fullerene cages could give rise to a myriad of novel molecules and materials. The existence of such species is now strongly supported by a growing body of experimental evidence. Fullerene& ndash;metal complexes generally thought to be endohedral are being produced and purified in milligram quantities, and their structure and properties are beginning to be explored
621 citations
TL;DR: In this article, the structures of pyrolytic carbon nanotubes (PCNTs) produced by thermal decomposition of hydrocarbon vapor (benzene at ca 1100°C) have been studied.
461 citations
TL;DR: In this article, it was shown that heating large ring systems above their melting point leads to 100% fullerene formation accompanied by the evaporation of a small carbon fragment (C1 or C3 for odd systems and C2 for even systems).
Abstract: THE discovery1–6 of the spherical carbon cage compound buck-minsterfullerene (C60) and the recent development of methods to produce it in bulk7 have led to an explosion in research in the physical and chemical properties of this unique species8,9. Nevertheless, the question of the formation mechanism of C60 (or of the other fullerenes) is still far from settled. We have shown elsewhere that carbon clusters in the gas phase develop from linear chains to planar ring systems to fullerenes as their size increases. One can easily envisage the transformation from chains to rings, but how the three-dimensional near-spherical fullerenes evolve from large planar rings is not obvious. Here we show that 'heating' these large ring systems above their 'melting' point leads to 100% fullerene formation accompanied by the evaporation of a small carbon fragment (C1 or C3 for odd systems and C2 for even systems). We propose a mechanism, based on these data, for efficient C60 production in carbon arcs.
353 citations
315 citations
TL;DR: A new material containing macroscopic quantities of hollow nanometric carbon onions with from 2 to about 8 graphitic shells, with outer diameters ranging from 3 to 10 nm (characterized by high-resolution electron microscopy), is produced by heat treatment of pure carbon soot.
287 citations
TL;DR: In this paper, the NMR chemical shifts of the bridgehead C-atoms and the 1J(C,H) coupling constants for the methano-bridge atoms were analyzed.
Abstract: A rapid and inexpensive method for the large-scale purification of C60 is the simple filtration of the toluenesoluble extract of commercial fullerene soot through a short plug of charcoal/silica gel with toluene as the eluent. Reactions of C60 with ethyl and tert-butyl diazoacetates in refluxing toluene lead to the formation of the (alkoxycarbonyl)methylene-bridged isomers 1a–3a and 1b–3b, respectively, which can be equilibrated, upon further heating, into the single compounds 1a and 1b, respectively. Isomers 1a/b possess the methano bridge at the 6–6 ring junction, whereas structures 2a/b and 3a/b are bridged at the 6–5 junction. A dramatic influence of local and π-ring current anisotropic effects of the fullerene sphere on the NMR chemical shifts of the methine protons in the bridge is observed: the chemical shifts of the protons located over a pentagon ring in 2a/b and over a hexagon ring in 3a/b differ by Δδ = 3.47 and 3.45 ppm, respectively. The analysis of the 13C-NMR chemical shifts of the bridgehead C-atoms and the 1J(C,H) coupling constants for the methano-bridge atoms reveals conclusively that the 6-5-ring-bridged structures 2a/2b and 3a/3b are π-homoaromatic (‘open’ transannular bond) and the 6-6-ring-bridged structures 1a/b are π-homoaromatic (‘closed’ transannular bond). The electronic absorption spectra show that π-homoconjugation in 2a/b and 3a/b represents a much smaller electronic perturbation of the original C60 chromophore than σ-homoconjugation in 1a/b. The results of this study demonstrate an impressive linkage between the chemistry of methano-bridged annulenes and methano-bridged fullerenes.
281 citations
TL;DR: Ion chromatography was used to determine the structure of pure carbon cluster ions as a function of size from C4 to C84, and results indicate that carbon grows first in linear chains, transforms to monocyclic planar rings at about C10, and forms new families of planar bi-, tri-, and tetracyclic rings at C20, C30, and C40.
Abstract: Gas-phase ion chromatography can separate ions that have the same mass but differ in isomeric structure or electronic configuration. The main features of this technique are briefly outlined, and applications to a series of problems in transition metal chemistry and carbon cluster chemistry are described. Examples in transition metal chemistry include state-selective reactivity, excited state deactivation, and state-selective ligand binding energies. For clusters, ion chromatography was used to determine the structure of pure carbon cluster ions as a function of size from C4 to C84. The results indicate that carbon grows first in linear chains, transforms to monocyclic planar rings at about C10, and forms new families of planar bi-, tri-, and tetracyclic rings at C20, C30, and C40, respectively. Fullerenes, which mysteriously appear at C30 and dominate by C50, are generated by heating the planar ring systems above an isomerization barrier rather than by growth of graphite precursors.
TL;DR: In this paper, the authors used a carbon arc reactor for the synthesis of a series of lanthanide elements and for iron group metals (Fe, Co, Ni) in the form of dicarbides within multilayered polyhedral carbon cages.
TL;DR: In this paper, the authors showed that carbon nanotubes and nanoparticles are more resistant to oxidation than other forms of carbon diamond, soot, graphite, and C[sub 60] studied previously under identical conditions.
Abstract: The oxidation of carbon nanotubes and nanoparticles has been studied by thermogravimetric analysis (TGA) in air. The maximum rate of weight loss took place at 695[degrees]C at a heating rate of 1[degrees]C/min. This result shows that the nanotubes and nanoparticles are more resistant to oxidation than other forms of carbon diamond, soot, graphite, and C[sub 60] studied previously under identical conditions. The TGA of the nanotubes/nanoparticles in argon showed no weight change or detectable thermal transformation up to 1000[degrees]C. 18 refs., 1 fig.
TL;DR: In this paper, the structure and stability of four possible isomers of C 24 and B 12 N 12 have been investigated by means of ab initio calculations at the MP2/DZP level.
TL;DR: Observations of frozen growth stages of buckytubes and derivatives suggest a helical growth mechanism analogous to that of crystal growth via screw dislocations and the possible steps in buckyball formation are outlined.
Abstract: Transmission electron microscopy (TEM) observations of graphite tubules (buckytubes) and their derivatives have revealed not only the previously reported buckytube geometries but also additional shapes of the buckytube derivatives. Detailed cross-sectional TEM images reveal the cylindrical cross section of buckytubes and the growth pattern of buckytubes as well as their derivatives. These observations of frozen growth stages of buckytubes and derivatives suggest a helical growth mechanism analogous to that of crystal growth via screw dislocations. The helicacy of buckytubes is analyzed by electron diffraction whereas the anisotropy of electronic structure is revealed by momentum transfer resolved electron energy loss spectrometry. Based on the TEM observations, it is proposed that buckytubes act as precursors to closed-shell fullerene (buckyball) formation and the possible steps in buckyball formation are outlined. In arc evaporation experiments in which residue rods (containing various amounts of buckytubes) were used as the starting anode for fullerene production, the amount of buckytubes in the rod was correlated with fullerene yield.
TL;DR: In this article, the metallofullerene LaC 82 has been isolated for the first time from the carbon soot using two-step liquid chromatographic method, and it was well identified as a stable molecule classified to a novel family of fullerene cage molecules.
TL;DR: In this article, the first self-assembled monolayer (SAM) of C[sub 60] was reported, its spectroscopic and electrochemical characterization, and initial chemistry with respect to its further modification.
Abstract: The authors report the first self-assembled monolayer (SAM) of C[sub 60], its spectroscopic and electrochemical characterization, and initial chemistry with respect to its further modification. The latter demonstration is significant since it illustrates the potential for growing covalently bound three-dimensional structures from fullerenes in a stepwise fashion via the self-assembly process. Two approaches may be taken towards fullerene self-assembly onto surfaces. Either a fullerene can be modified in solution with functionalities that allow for self-assembly, or a surface may be chemically modified with a reagent that undergoes a bond-forming reaction with a fullerene in solution. Herein, the authors report success via the latter approach. 13 refs., 1 fig., 1 tab.
TL;DR: The formation of the tubes under the quasi-free conditions suggests that the growth to tubular rather than spherical configurations is preferred for "giant fullerenes."
Abstract: Fullerene tubular structures can be generated by vapor condensation of carbon on an atomically flat graphite surface. Scanning tunneling microscope (STM) images revealed the presence of tubes with extremely small diameters (from 10 to 70 angstroms), most of which are terminated by hemispherical caps. Atomic resolution images of such structures showed that the tubes have a helical graphitic nature. The formation of the tubes under the quasi-free conditions suggests that the growth to tubular rather than spherical configurations is preferred for "giant fullerenes."
TL;DR: Experimental studies of the annealing of the non-fullerene C60+ ions indicate that they can be converted into the fullerene and an isomer that appears to be a large monocyclic ring, suggesting that this is a relatively stable non-spheroidal form of these all carbon molecules.
Abstract: Laser vaporization of graphite generates C60+ cluster ions that are fullerenes and a mixture of roughly planar polycyclic polyyne ring isomers. Experimental studies of the annealing of the non-fullerene C60+ ions indicate that they can be converted (in the gas phase) into the fullerene and an isomer that appears to be a large monocyclic ring. Some fragmentation is associated with conversion to the fullerene geometry, but the majority of the non-fullerene C60+ isomers are cleanly converted into an intact fullerene. The emergence of the monocyclic ring (as the clusters are annealed) suggests that this is a relatively stable non-spheroidal form of these all carbon molecules. The estimated activation energies for the observed structural interconversions are relatively low, suggesting that these processes may play an important role in the synthesis of spheroidal fullerenes.
TL;DR: In this article, the formation of C60 and C70 by pyrolysis of naphthalene at ∼1,000 °C was reported, showing that closed fullerene cages can be built from well defined aromatic fragments.
Abstract: THE formation of bulk quantities of C60 by arc discharge between carbon electrodes in an atmosphere of helium1 or argon2,3 has led to an explosion in fullerene research. Methods for improving the rate of fullerene production have included increasing the reactor size and the diameter of the carbon rods, and varying the rate of rod consumption and helium pressure4. Systems using several rods have also been employed5,6. The ideal method, however, would involve a continuous process that does not require rod replacement. Approaches using carbon granules6 and powders7 have been reported, as well as combustion methods using hydrocarbons8,9. Here we report the formation of C60 and C70 by pyrolysis of naphthalene at ∼1,000 °C. C60 and C70 are formed by the 'patching together' of six and seven naphthalene molecules respectively, as demonstrated by mass-spectrometric analysis of intermediate products. These results point to a continuous method of fullerene formation, and also show that closed fullerene cages can be built from well defined aromatic fragments.
TL;DR: In this article, a methano analog of buckminsterfullerene epoxide (C[sub 60]O]O) was derived and structure elucidation of 1,2-methanobuckminster fullerene (2, C[sub 61]H[sub 2]).
Abstract: Recently we reported the synthesis, isolation, and characterization of 1, the first fullerene epoxide (C[sub 60]O). We describe herein the generation and structure elucidation of 1,2-methanobuckminsterfullerene (2, C[sub 61]H[sub 2]), the parent fullerene cyclo propane. This is the methano analog of buckminsterfullerene epoxide 1. NMR coupling constants were employed to differentiate closed (fullerene) and open (fulleroid) isomers. We are currently exploring the chemical and physical properties of the [6,6] fullerene cyclopropanes. 15 refs., 1 fig.
TL;DR: In this paper, the authors used ab initio quantum-chemical calculations to show that fullerene annealing happens more readily than fragmentation, and that both are intimately related.
Abstract: WHEN fullerenes1,2 are fragmented by laser irradiation, they lose C2 fragments and retain a closed carbon cage3. The detailed mechanism of this process remains unknown, although survival of the cage implies that annealing (rearrangement of the bonding) must play an important role3,4. Here we use ab initio quantum-chemical calculations to show that fullerene annealing happens more readily than fragmentation, and that both are intimately related. Our findings imply that the assumptions commonly made about fullerenes5—that they are composed of five- and six-membered rings of sp2 carbons— are not valid under high-energy conditions. In particular, the appearance of sp3 carbon and seven-membered rings is central in both the annealing and fragmentation processes. Our theoretical predictions imply that the high-energy processes of fullerene growth6–11 and coalescence12 are much richer than previously thought, and that their mechanisms may also involve structures containing sp3 carbon and seven-membered rings. Our results may aid in the design of experimental methods for controlling the nature of fullerene cages (for example, doping, opening and re-closing them).
TL;DR: In this article, the coupling of compact dendritic macromolecules with prefunctionalized fullerenes is described, and two dendrimers are attached to the surface of the fullerene.
Abstract: The coupling of compact dendritic macromolecules with prefunctionalized fullerenes is now described. This synthetic strategy, involving two species containing a precise number of functional groups, gives greater control over the formation of polymer-fullerene hybrid structures. Phenol-functionalized fullerenes have been prepared by reaction of C[sub 60] with bis(p-methoxyphenyl)diazomethane followed by hydrolysis of the methyl ethers with BBr[sub 3]. This synthesis has been tailored to yield a 6-6 bridged methano fullerene derivative carrying only two phenolic sites as the major product. Polyether dendrimers prepared by the convergent synthesis route are ideally suited for attachment to phenol-functionalized buckyballs since they carry a single electrophilic site at their focal point, and their attachment to phenolic moieties has been studied extensively. The formation of fullerene-bound dendrimers was accomplished by reaction of each of the two phenolic groups located at the surface of the functionalized fullerene with the single benzylic bromide group at the focal point of a fourth-generation dendrimer in the presence of K[sub 2]CO[sub 3]. Purification by flash chromatography or precipitation gave only partial separation of the products; as a result, preparative SEC was used to obtain samples of each of the products. A [sup 1]H NMR spectrum of the desired product, in whichmore » two dendrimers are attached to the surface of the fullerene, is shown. 9 refs., 2 figs.« less
TL;DR: The present studies not only provide new insights into fullerene formation mechanisms but also raise the possibility of tailoring the size distributions of fullerenes by variation of the appropriate properties of the precursors.
Abstract: The availability of macroscopic quantities of fullerenes has resulted in a vast number of physical and chemical studies of these new materials. However, the mechanisms that lead to the formation of these spherical carbon allotropes are not well understood. Mass spectral evidence has been obtained for the size-selective growth of fullerenes through the coalescence of cyclo[n] carbons, molecular carbon allotropes consisting of monocyclic rings with n carbon atoms. Whereas coalescence of cyclo[30]carbon (cyclo-C30) produces predominantly buckminsterfullerene (C60), the smaller rings cyclo-Cl8 and cyclo-C24 preferentially produce fullerene C70 through distinct intermediates. The present studies not only provide new insights into fullerene formation mechanisms but also raise the possibility of tailoring the size distributions of fullerenes by variation of the appropriate properties of the precursors.
TL;DR: In this article, an X-ray crystal structure was obtained from a benzene clathrate of comparison compound 2, synthesized by Diels-Alder reaction of C60 with the ortho-quinodimethane derived from 1,2-bis(bromomethyl)-4,5-dimethoxybenzene (4).
Abstract: A fullerene derivative 1 of benzo[18]crown-6 was obtained by Diels-Alder addition of fullerene[60](C60) to the ortho-quinodimethane prepared in situ from 4,5-bis(bromomethyl)benzo[18]crown-6 (3) with Bu4NI in toluene. Extraction experiments show that the complexation of K+ ions strongly increases the solubility of 1 in protic solvents like MeOH. Using Langmuir-Blodgett techniques, monolayers of the highly amphiphilic fullerene-derived crown ether 1 and its K+ ion complex were prepared. An X-ray crystal structure was obtained from a benzene clathrate of comparison compound 2, synthesized by Diels-Alder reaction of C60 with the ortho-quinodimethane derived from 1,2-bis(bromomethyl)-4,5-dimethoxybenzene (4). Both the fullerene molecule 2 and the benzene molecule are fully ordered in a crystal packing which is stabilized by intermolecular van-der-Waals contacts between the benzene ring and the C-spheres, intermolecular C…C contacts between the C60 moieties, and intermolecular O…C contacts between the O-atoms of the veratrole moieties and fullerene C-atoms.
TL;DR: In this paper, the authors studied the electronic structures, equilibrium geometries, and binding energies of the title molecules at the self-consistent field (SCF) Hartree-Fock level of theory employing basis sets of double-zeta quality.
Abstract: Recent experiments have demonstrated that C28 is the smallest fullerene cage that successfully traps elements in its inside. In this work, we have studied the electronic structures, equilibrium geometries, and binding energies of the title molecules at the self‐consistent field (SCF) Hartree–Fock level of theory employing basis sets of double‐zeta quality. The empty C28 fullerene is found to have a 5A2 open‐shell ground state and behaves as a sort of hollow superatom with an effective valence of 4, both toward the outside and inside of the carbon cage. The theoretical evidence suggests that C28H4 and C28F4 should be stable molecules. The possibility of simultaneous bonding from the inside and outside of the C28 shell, as in (Ti@C28)H4, is also explored. Our calculations show that the binding energy of the M@C28 species is a good indicator of the success in experimentally trapping the metal atoms (M) inside the fullerene cage. Based on these results, we propose that elements with electronegativities smaller than 1.54 should form endohedral fullerenes larger than a minimum size which depends on the ionic radius of the trapped atom. This qualitative model, correctly reproduces the available experimental evidence on endohedral fullerenes.
TL;DR: An expression for the electron-phonon coupling strength in fullerene nanotubules is derived within the tight-binding model and it is shown that the interaction of electrons with longitudinal acoustic phonons gives rise to intraband scattering but not to interband scattering.
Abstract: An expression for the electron-phonon coupling strength in fullerene nanotubules is derived within the tight-binding model It is shown that the interaction of electrons with longitudinal acoustic phonons gives rise to intraband scattering but not to interband scattering; the reverse is true for interaction of electrons with transverse phonons in the tangential direction It is estimated that under ideal circumstances, the electrical conductivity of metallic fullerene nanotubules could be more than an order of magnitude larger than that of copper