Stability Of Fullerenes Research Articles

Local-density-functional study of the fullerenes, graphene and graphite

Large basis set local-density-functional calculations on fullerenes, graphene and graphite suggest that fullerene stability increases monotonically with the number of carbon atoms (N), and is nearly linear in 1/N. is less stable energetically than and higher fullerenes, despite the apparent preference for in nature. The heat of formation found here for relative to graphite is in good agreement with experiment, while the heat of formation for graphene relative to graphite is overestimated by a factor of two.

Thermodynamics of intercalation in C 60 fullerite and stability of cubic close-packed fulleride compounds

Stability of known or hypothetical fullerene C 60 intercalation compounds was investigated through a donor-acceptor scheme. A thermodynamic cycle was employed, requiring evaluation of energy costs related with charge transfer and formation of the intercalated solid. Strongly exothermic reactions are predicted in several cases, especially with some elements of the rare-earth series, which should consequently form stable, low dimensional phases. These latter might be interesting candidates for superconductivity, as alkali-doped C 60.

Fullerene stability and structure

Abstract Fullerenes are all-carbon polyhedral cage molecules in which each atom is directly bonded to three neighbours and the n atoms and 3n/2 edges are arranged in 12 pentagonal and n/2–10 hexagonal rings. Simple mathematical and physical models can be used to count and construct isomers, to assign symmetries, to estimate geometries, to predict the (rare) appearances of property closed πelectron configurations and to rationalize trends in overall stability in this new and growing family of molecules.

Local softness and hardness as reactivity indices in the fullerenes C 24C 76

The condensed local softness, s k + or condensed fukui function, f k +, approximated by Mulliken atomic charge differences, are used as a descriptor of the regioselectivity for the fullerenes (from C 24 to C 76) towards a nucleophilic attack. In general the results, which are in agreement with experimental data, can be interpreted in terms of a pyramidalization angle effect, soft-hard alternations and softness delocalization. The local hardness on the most reactive carbon atom in each fullerene turns out to be a valuable descriptor of the intermolecular reactivity sequence. The maximal hardness principle is used to discuss the stability for the larger fullerenes (C 50, C 60, C 70 and C 76). The calculated hardness, approximately calculated as the LUMO-HOMO energy difference, confirms the fact that C 60 and C 70 are the most stable fullerenes.

The phaseon line: a new criterion for the stability of fullerenes

The phaseon line: a new criterion for the stability of fullerenes

Propensity Rules for the Stability of Odd-Numbered Fullerenes: A Semiempirical Proposal

The structures of C119 and C129, the two lowest odd-numbered fullerenes, are investigated by semiempirical quantum chemical calculations. In the process, the use of a recently proposed parametrization for a tight-binding Extended-Huckel model is validated to study the relative stability of fullerenes. Three general routes for the generation of the structures of odd-numbered fullerenes are described and used to generate systems that can be loosely characterized as having either a four-membered ring or a patch of adjacent pentagons, or a set of multiple connections between the cages of the pristine fullerenes. The structures of the six isomers of C119 obtained in this manner are optimized and it is confirmed that the most stable isomer of C119 has C2 symmetry and forms three bonds between the C59 and the C60 moieties. By analogy with C119, 56 structures of C129 are generated and their geometries are optimized. As in the case of C119, it is found that the most stable isomer of C129 can be formed both from th...

Bond Resonance Energies and Kinetic Stabilities of Charged Fullerenes

The bond resonance energy (BRE) represents the contribution of a given {pi} bond in a molecule to the topological resonance energy. Kinetic stabilities of fullerenes and their molecular ions were interpreted successfully in terms of the BREs. Fullerene cations have highly reactive {pi} bonds with large negative BREs. In contrast, few {pi} bonds in multiply charged fullerene anions have large negative BREs. Thus, fullerenes and their molecular ions with highly antiaromatic {pi} bonds are predicted to be incapable of formation and survival during the synthetic process. Such a trend in kinetic stability is in agreement with experiment. 38 refs., 1 fig., 2 tabs.

Assessment of the Stability of Heterohedral Fullerenes: A Theoretical Analysis of C60-xNx and C60-xBx Where x = 1 and 2

In this work we discuss limitations in the stability of monosubstituted heterohedral fullerenes. Both quantum and molecular mechanical approaches are used to understand the limits in bonding and structural characteristics of these materials. Both the electronic structure calculations and the molecular mechanics study suggest that greater inherent stability exists in the monosubstituted boron fullerene compared with the equivalent nitrogen analog. This is somewhat consistent with the sparse experimental information provided for N-doped fullerenes. In addition, structural comparisons show significantly greater distortion of the fullerene framework for the nitrogen-substituted material. Electronic structure calculations predict greater disruption of bonding near the substitution site for C{sub 59}N in comparison with C{sub 59}B, and the energy trends from these calculations suggest that the stability of the C{sub 59}N is considerably lower than that of C{sub 59}B. Furthermore, the electronic structure calculations suggest that C{sub 59}N{sup +} may be more stable than the parent neutral material. Disubstituted heterohedral fullerenes have been analyzed utilizing similar electronic requisites for stability. 25 refs., 5 figs., 5 tabs.

Stability of fullerenes with four-membered rings

Fullerenes with four-membered rings with up to 60 atoms were systematically generated and their stability examined by the conjugated circuits (CC) model and the topological resonance energy (TRE) model. As none of the models accounts for strain, which is important in spherically shaped conjugated systems with four-membered rings, the results are only qualitative. Values of resonance energy obtained by the two models show remarkable disagreement. Isomers selected as the most stable are quite different in dependence on the criterion used. The structures selected by TRE possess a small number or no four-membered rings (for C 60, buckminsterfullerene was selected), while those selected by the CC model sometimes possess greater numbers (up to 6) of four-membered rings, paired by a common edge.

Stability of small fullerenes C n (n=36,40 and 60): A topological and molecular orbital approach

By semi-empirical molecular orbital calculations stability of fullerenes was analyzed in terms of topological parameters, such as the number of special fragments and the number of three types of abutting bonds between two 5-membered rings. Relative stability was compared by AM1 method for all spectrally distinct closed-shell isomers of C36 and C40 fullerenes, and for some closed-shell isomers of C60 fullerene. Molecular geometries of these fullerenes were also optimized. Their relative stabilities were well explained by the instability of abutting bonds.

Stability of small fullerenes C

Stability of small fullerenes C

Kinetic stability of fullerenes with four-membered rings

The bond resonance energy (BRE, Ebr) represents the contribution of a given π bond in a molecule to the topological resonance energy (TRE, Etr). It is useful for seeking the reactive sites in a cyclic π-electron system. Calculated Ebr support of the view that some fullerences with two four-membered and four fewer five-membered rings might be more stable than the normal fullerence isomers. Some such fullerenes have no highly reactive π bonds, presumably being capable of formation and survival during synthetic processes.

Topological resonance energy predictions of the stability of fullerene clusters

The topological resonance energies (TRE) for various fullerene clusters (C 20 to C 60) have been computed and based on this, stabilities of fullerenes are discussed. Trend in stability predicted by the TRE model is compared with predictions from the conjugated circuit model as well as the MNDO and ab initio methods. Reasonable agreement is found between the TRE model and rigorous quantum mechanical methods.

Fullerene stability under shock-wave and static loading

Fullerene stability under shock-wave and static loading

Structural defects and the shape of large fullerenes

Motivated by the recent experimental observation of nearly spherical multi-layer fullerenes, we investigate theoretically the role of thermally generated structural defects on the shape and stability of large fullerenes by equilibrium statistical mechanics methods. Low energy defects are generated via atom insertions and bond rotations and the resulting structures are relaxed using realistic atomic potentials. The lowest defect formation energies are about 1 eV. A free energy analysis shows that large fullerenes will contain a substantial number of such defects at high temperatures. The presence of these defects effectively spreads out the sharp “kinks” associated with the faceted ground state structure, leading to a more spherical cage of a uniform curvature.

Thermal stability of fullerene (C 70) on the Si(100) 2×1 surface studied with FI-STM

We have studied the thermal stability of fullerene C 70 adsorbed on the Si(100)2×1 surface with the field ion-scanning tunneling microscope. The results show that the first layer of C 70 adsorbed considerably strongly due to the existence of Si dangling bonds on the surface. The first layer passivated the surface efficiently so that the multilayer crystalline film could be grown as close-packing array. The C 70 above the first layer can be easily desorbed at temperatures above approximately 250°C, which is similar to that of bulk C 70. In contrast to that, the first layer remains stable without any evidence of cage breaking or reordering until at temperatures above 1000°C, resulting in well-ordered islands: β-SiC(100)3×2 surface, according to our STM observations. The present work reveals a novel fullerene property on the Si(100)2×1 surface.

Thermal Stability in Pure Oxygen of Soot Generated During the Production of C60by the Contact Arc Vaporization of Graphite

Abstract The thermal stability in oxygen of residual soot, after extraction with toluene, has been found to be lower than that of C60. Since the residual soot has been shown from previous studies to contain higher fullerenes, the present results suggest that the oxidative stability of higher fullerenes, rather surprisingly, is lower than that of C60.

STRUCTURE, STABILITY, AND ELECTRONIC PROPERTIES OF LARGE FULLERENES

The recent development in understanding the structures, relative stability, and electronic properties of large fullerenes is reviewed. We describe an efficient scheme to generate the ground-state networks for fullerene clusters. Combining this scheme with quantum-mechanical total-energy calculations, the ground-state structures of fullerenes ranging from C 20 to C 100 have been studied. Fullerenes of sizes 60, 70, and 84 are found to be energetically more stable than their neighbors. In addition to the energies, the fragmentation stability and the chemical reactivity of the clusters are shown to be important in determining the abundance of fullerene isomers.

Stability of multishell fullerenes.

We investigate the equilibrium geometry of very large carbon clusters with special emphasis on nested multishell fullerene derivatives of spherical, cylindrical, and conic shape. For cluster sizes above 20 atoms, we find spherical shapes to be most stable. For very large sizes, a transition from single-shell fullerenes to multishell structures, locally similar to graphite, is energetically favored by the weakly attractive interaction between the shells.

Stable derivatives of small fullerenes

Recent developments in experiment and theory have enhanced our understanding of fullerene stability and reactivity to the point where predictions may be made concerning the probable existence of specific fullerenes and their derivatives. One approach, considered here for small fullerenes (C n , n<10) - which cannot have isomers in which all pentagons are isolated - invokes the concepts of localised surface stability domains and angle strain release.