Combined topological and energy analysis of the annealing process in fullerene formation. Stone–Wales interconversion pathways among IPR isomers of higher fullerenes

Ōsawa, Eiji; Ueno, Hiroshi; Yoshida, Mitsuho; Slanina, Zdenêk; Zhao, Xiang; Nishiyama, Minobu; Saito, Hiroko

doi:10.1039/a706423c

Cited by 66 publications

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“…The computations start from topologically generated structures [45,46] with correct bond connectivities. All such 134 C 94 IPR topologies possible were submitted to the MNDO, PM3, AM1, and SAM1 geometry optimizations.…”

Section: Resultsmentioning

confidence: 99%

C94 IPR isomeric set: large-scale computations of relative stabilities based on the Gibbs function

Slanina

Zhao

Uhlı́k

et al. 2003

Journal of Molecular Structure: THEOCHEM

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At present C 94 is one of the highest sets of isomeric fullerenes that has been characterized by 13 C NMR spectra. This contribution reports quantum-chemical computations on the C 94 system. The complete set of 134 isolated-pentagon-rule isomers of C 94 is described by four semiempirical quantum-chemical methods (MNDO, AM1, PM3, and SAM1). The C 94 energetics is also checked with Hartree -Fock SCF calculations in the standard 4-31G basis set (HF/4-31G). The calculations point out a C 2 structure as the system ground state. As energetics itself cannot produce reliable relative stabilities at high temperatures, entropy terms are also computed and the relative-stability problem is entirely treated in terms of the Gibbs function. The lowest-energy structure remains the most populated isomer at higher temperatures. However, several other structures show significant populations at higher temperatures. The six most populated species at the AM1 computational level read: C 2 ; C 2 ; C 1 ; C 1 ; C s ; and C 2 : This selected six-membered isomeric set indeed contains the four symmetries observed in the available experiment (C 2 ; C s ; C 2 ; and C 2 ). This incidence represents a good agreement with the experiment and can be viewed as another evidence that the supposed inter-isomeric thermodynamic equilibrium does exist in experiments. q

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Section: Resultsmentioning

confidence: 99%

C94 IPR isomeric set: large-scale computations of relative stabilities based on the Gibbs function

Slanina

Zhao

Uhlı́k

et al. 2003

Journal of Molecular Structure: THEOCHEM

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“…We searched all topologically possible pathways for the reaction with the aid of a graphical search program. 12,24 Among these, we identified the shortest pathway, which is likely associated with the fastest fusion mechanism. This pathway involves only 23 GSW transformations and is depicted in Fig.…”

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confidence: 99%

“…GSW transformations are known to require much lower activation energies than processes involving bond breaking, and have been studied extensively in sp 2 bonded carbon structures. 12,19,20 A possible GSW pathway for fusion has been suggested based on a "qualitative reasoning assisted search" for structures along the minimumenergy path. 21 The initial step in that study, however, is a reaction between two pentagons facing each other, which is energetically unaccessible.…”

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confidence: 99%

“…We show that large-scale structural changes, including fusion, can be achieved by a finite sequence of generalized Stone-Wales transformations, which involve only bond rotations and avoid bond breaking. Using a graphical search program, 12 we determine the optimum reaction pathway for thermal fusion of fullerenes. Search of the phase space by the "string method" provides detailed information about the optimum pathway, including the identification of activation barriers and transition-state geometries.…”

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Microscopic mechanism of fullerene fusion

et al. 2004

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Combining total energy calculations with a search of phase space, we investigate the microscopic fusion mechanism of C 60 fullerenes. We find that the ͑2+2͒ cycloaddition reaction, a necessary precursor for fullerene fusion, may be accelerated inside a nanotube. Fusion occurs along the minimum energy path as a finite sequence of Stone-Wales transformations, determined by a graphical search program. Search of the phase space using the "string method" indicates that Stone-Wales transformations are multistep processes, and provides detailed information about the transition states and activation barriers associated with fusion. The discovery of fullerenes 1 and nanotubes 2 has ignited strong interest in these and related carbon nanostructures. Due to the unusual stability of the graphitic sp 2 bond, largescale structural changes in bulk fullerene crystals occur only under extremely high pressures and temperatures.3,4 On the other hand, fullerenes in nanotube peapods 5 have been observed to fuse 6,7 at relatively low temperatures near 1100°C, significantly below the decomposition temperature of fullerenes 8 or graphite 9 near 4000°C. No information is available about the detailed fusion process except the obvious conclusion that strong sp 2 bonds should not be broken during structural rearrangements leading to fusion. In view of the fact that even minor structural changes in carbon nanostructures may modify significantly their physical properties, including magnetism, 10,11 there is additional interest in understanding fusion as a way to control large-scale structural transformations.Here we study the microscopic fusion mechanism of fullerenes. We show that large-scale structural changes, including fusion, can be achieved by a finite sequence of generalized Stone-Wales transformations, which involve only bond rotations and avoid bond breaking. Using a graphical search program, 12 we determine the optimum reaction pathway for thermal fusion of fullerenes. Search of the phase space by the "string method" provides detailed information about the optimum pathway, including the identification of activation barriers and transition-state geometries. We find the fusion process to be exothermic. The fusion dynamics is fast in spite of the formidable total activation barrier close to 5 eV, associated with each Stone-Wales transformation. These bond rotations turn out to be multistep processes with lower individual activation barriers.We calculate the total energy of the fullerene system using an electronic Hamiltonian that had been applied successfully to describe the formation of peapods, 13 multiwall nanotubes, 14 the dynamics of the "bucky shuttle," 15 and the melting of fullerenes. 8 Our numerical results are compared to those of ab initio density functional calculations, which use a numerical basis to represent localized atomic orbitals, 16 and which have been applied successfully to nanotubes and fullerenes. 17 Structural optimization is performed using the conjugate gradient technique. Our total energy formalism describe...

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“…So könnte man festzustellen, ob die gewünschten Isomere isolierbar sind oder ob sie bei der Synthese zu einem (oder mehreren) stabileren Isomeren umlagern. [62] Exotischere Zielverbindungen stellen 13 C-markiertes C 60 , Azafullerene oder andere Heterofullerene dar. Die Synthese von mehrfach 13 C-markiertem C 60 könnte klären, ob ein einziges Isotopomer als Produkt erhalten wird oder ob die Kohlenstoffatome unter den FVP-Bedingungen [63,64] oder bei einer anschließenden Bestrahlung [65] durchmischt werden.…”

Section: Die Anwendung Der Beschriebenen Methoden Bei Der Synthese Vounclassified

Methoden zur chemischen Synthese von Fullerenen

Scott

2004

Angewandte Chemie

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Das bekannteste Fulleren, C60 , wurde mit chemischen Methoden synthetisiert. Über zehn Jahre lang wurden im Labor des Autors bei der Synthese und dem Studium von offenen geodätischen Polyarenen Erfahrungen gesammelt, auf deren Grundlage die Strategie und Methodik für die Herstellung einer Vorstufe aus 60 Kohlenstoffatomen und deren Schließung zum Fulleren ausgearbeitet wurden. In diesem Aufsatz beschreibt der Autor aus seiner persönlichen Perspektive, wie die neuen Synthesemethoden entwickelt und eingesetzt wurden.

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Combined topological and energy analysis of the annealing process in fullerene formation. Stone–Wales interconversion pathways among IPR isomers of higher fullerenes

Cited by 66 publications

References 36 publications

C94 IPR isomeric set: large-scale computations of relative stabilities based on the Gibbs function

C94 IPR isomeric set: large-scale computations of relative stabilities based on the Gibbs function

Microscopic mechanism of fullerene fusion

Methoden zur chemischen Synthese von Fullerenen

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