On the Formation and Stability of Fullerenes

Fullerenes (especially the higher ones) degrade to an insoluble material on storage in air. The C_2v(II) isomer of [78]fullerene is completely degraded after storage for 5 months. The extreme instability may account for the variable yields of this isomer obtained by different research groups. Strong heating of KBr discs of these insoluble materials produces CO₂ showing that they are oxygen containing. Given this inherent instability of fullerenes, the question arises as to why they are formed in the first place. It is argued that the formation is not a unique consequence of the need to eliminate dangling bonds produced during carbon vaporisation by the arc-discharge procedure. Rather, fullerene formation is favoured by a higher intramolecular dangling-bond collision frequency (i.e. much higher Arrhenius A-factor) for cage closure compared to the intermolecular collisions that lead to the more stable graphitic sheets.     

Heterohedral Fullerenes and Nanotubes: Formation and Characteristics

Both theoretical and experimental studies show that carbon atom(s) can be substituted in a fullerene cage or in a nanotube by “guest” atom(s) or molecule(s) to form stable structures. This new class of networked carbon nanostructures called heterofullerenes and heteronanotubes is presented and their interesting properties and synthesis routes are discussed.     

The Formation of Fullerenes from Sonic Velocity Gaseous Carbon

Abstract

A contact are and adiabatic expansion hybrid reactor has been utilized to provide a controlled cooling process of gaseous carbon species capable of attaining very high velocities. Both vaporization and annealing temperatures and annealing time were found to be impartant for the formation of fullerenes. Immediate rapid quenching of gaseous carbon resulted in the reduction of fullerene yields. However, rapid quenching was demonstrated to improve the fullerene yield by preserving the as-grown fullerenes in the high temperature annealing process.     

The Formation of Fullerenes from Sonic Velocity Gaseous Carbon

A contact are and adiabatic expansion hybrid reactor has been utilized to provide a controlled cooling process of gaseous carbon species capable of attaining very high velocities. Both vaporization and annealing temperatures and annealing time were found to be impartant for the formation of fullerenes. Immediate rapid quenching of gaseous carbon resulted in the reduction of fullerene yields. However, rapid quenching was demonstrated to improve the fullerene yield by preserving the as-grown fullerenes in the high temperature annealing process.     

On the Number of Spanning Trees in Fullerenes

A simple method, based on the spectrum of the Laplacian matrix, is proposed for the enumeration of spanning trees of fullerenes.     

催化剂种类对纳米洋葱状富勒烯形成的影响

研究了相同电弧放电条件下,不同催化剂(Fe、Al)掺杂对洋葱状富勒烯形成的影响.用高分辨透射电子显微镜(HRTEM)和X-射线衍射(XRD)对产物进行了观察与表征.结果表明,Fe作催化剂形成的洋葱状富勒烯产量和质量都优于Al作催化剂的情况,Fe的催化活性较Al的高,是制备洋葱状富勒烯的一种更加有效的催化剂.     

On Assembling Fullerenes from Identical Fragments

A combinatorial covering of the fullerene graph by identical fragments has been considered. Fragments involved in various proposed mechanisms for fullerene formation were examined. A search for Hamiltonian circuits has been also undertaken.     

On the Size Dependence of Standing Waves in Tubular Fullerenes

Summary

We present an analysis of principal vibrational modes whose propagation creates the standing waves along the lateral surfaces of the elongated fullerenes.

We deduce the recurrence rules determining the possibility of resonances between the skew and vertical modes, as well as the appearance of isolated standing waves with nodes in the elongated fullerenes C_N with N = 50 + 10k, k= 1,2,3….

We discuss briefly the influence of different vibrational spectra on the mechanical stability of C_N-elongated fullerenes, and its impact on the relative rate of their production.

     

Time-Resolved Mass Spectrometric Studies of Fullerenes and Endohedral Fullerenes

Abstract

The energetics and dynamics of C₂ evaporations from fullerene radical cations C_n ^?+ were studied with and without ion trapping techniques. Electron space charge trapping was applied in electron ionization experiments. RF trapping in a Paul type ion source was applied for Laser MPI. Appearance energies, kinetic energy releases and metastable fractions were determined. the experimental data were modeled by finite heat bath theory (FHBT) and by RRKM/QET. Evaporation (binding) energies as well as conventional and intrinsic kinetic shifts were deduced. Our results support the following conclusions: (a) C₆₀ sits on the leading edge of a magic shell, with C₅₈ only slightly less stable and C₆₂ considerably less stable than C₆₀; (b) Dissociative decay is able to compete with radiative decay of C₆₀ ^?+ only at internal energies in excess of 37.6 eV (T_b>2300 K); (c) a Ne endohedral atom has a slightly stabilizing effect on the C₆₀ ^?+ cage whereas La is strongly stabilizing the C₈₂ ^?+ cage; (d) C₂ loss is a true evaporation in the sense of having a loose transition state with no reverse activation energy; (e) the C₂ evaporations are statistical in nature and theories such RRKM/QET and FHBT are in excellent agreement with experimental observations.     

Dependence of Endohedral Fullerenes Formation on Laser Ablation Parameters of Carbonaceous Materials

Endohedral fullerenes containing yttrium atoms were produced by laser irradiation of mixtures of carbonaceous compounds and yttrium oxide targets. The laser irradiance, the temperature, the ablation wavelength and the nature of the target were studied more precisely. The analyses are performed with a Laser Microprobe coupled with Mass Spectrometry (LMMS). The study of spectral fingerprints on both positive and negative modes allows to evaluate the relative distribution of metalfofullerenes compared to classical fullerenes according the laser ablation parameters.     

Fullerenes and Viruses

Abstract

It is well known that any, sometimes very small, changes in the chemical structure can lead to the dramatic changes in biological properties. Therefore it is necessary to divide into two different topics the studies of biological properties of fullerene and fullerene‐like compounds. In the enormous variety of data on the biological activity of fullerenes it is possible to select some with defined mechanism of action. This selection showed that in case of using the fullerene‐containing compositions the main mechanisms of drug action, namely unspecific, specific (ligand–receptor) interaction and membranotropic can be obtained. Therefore fullerenes as compounds with broad biological potential are very promising not only for the design of antiviral compounds, but also for the design of various types of drugs.     

Photophysical and Photochemical Properties of the Fullerenes

This article primarily reviews the recent work of this laboratory on the photophysical and photochemical properties of the fullerenes, C₆₀ and C₇₀, in solution. Properties of the excited singlet and triplet states of them have been characterised by static and transient fluorescence spectroscopy. Charge and/or proton transfer dynamics in ground and excited singlet state of the fullerenes with the amines have been investigated in detail. Strong evidence has been obtained for weak interaction between the fullerenes and the aromatic solvents, like benzene, toluene etc. A novel method has been described to solubilise C₆₀ in aqueous solution via formation of inclusion complex with γ-cylodextrin.     

On the Limitation of Net Algorithm for Enumerating Isomeric Structures of Giant Fullerenes

Abstract

Application of our net algorithm to the generation of all possible IPR isomers for giant fullerenes C_n, n=102 to 120, missed nine out of 39,621 possible structures. Analysis revealed that the omission of too small and too large cap triangles was the reason. Within the range of fullerenes studied, the missed structures are of high-energy and do not affect the distribution of significantly low-energy isomers.     

Terrestrial and Extraterrestrial Fullerenes

This paper reviews reports of occurrences of fullerenes in circumstellar media, interstellar media, meteorites, interplanetary dust particles (IDPs), lunar rocks, hard terrestrial rocks from Shunga (Russia), Sudbury (Canada) and Mitov (Czech Republic), coal, terrestrial sediments from the Cretaceous-Tertiary-Boundary and Permian-Triassic-Boundary, fulgurite, ink sticks, dinosaur eggs, and a tree char. The occurrences are discussed in the context of known and postulated processes of fullerene formation, including the suggestion that some natural fullerenes might have formed from biological (algal) remains.     

Shungite Carbon and Fullerenes

Abstract

Thermpgravimetry method applied to shungite carbon (ShC) was the next step which testified its similarity with fullerenes. Fullerene-like approach suggested earlier was helpful in understanding shungite nature. ShC behavior under heating in air confirmed the structure ordering and its metastability.     

Shungite Carbon and Fullerenes

Thermpgravimetry method applied to shungite carbon (ShC) was the next step which testified its similarity with fullerenes. Fullerene-like approach suggested earlier was helpful in understanding shungite nature. ShC behavior under heating in air confirmed the structure ordering and its metastability.     

On the Limitation of Net Algorithm for Enumerating Isomeric Structures of Giant Fullerenes

Application of our net algorithm to the generation of all possible IPR isomers for giant fullerenes C_n, n=102 to 120, missed nine out of 39,621 possible structures. Analysis revealed that the omission of too small and too large cap triangles was the reason. Within the range of fullerenes studied, the missed structures are of high-energy and do not affect the distribution of significantly low-energy isomers.     

EPR of Graphite and Fullerenes

Analysis of the EPR results for graphite and fullerenes has led to the development of a model for the g-factor in follerene based on the analogy between graphite and fullerene. Pressure dependence of g-factor in C₆₀ powder confirms the validity of this model. ¹³C hyperfine splitting of_a0.36 mT in pristine fullerene is also reported. The g-factors of C₆₀^-1 and C₆₀^-3 in a solution and in a different K°C₆₀ fullerides are presented. C₆₀⁺ⁿ states should be described by the spectroscopic splitting factor larger than that of a free spin.     

Theory for the Growth of Fullerenes

Abstract

In view of recent experiments we extend our previous growth model for fullerene formation. It becomes clear how a high efficiency of C₆₀ formation is achieved. We estimate the size dependence of intermediate structures along the most efficient growth route and furthermore the stability of Si_2o, Ge_2o vs. the unstable C_20-     

Theory for the Growth of Fullerenes

In view of recent experiments we extend our previous growth model for fullerene formation. It becomes clear how a high efficiency of C₆₀ formation is achieved. We estimate the size dependence of intermediate structures along the most efficient growth route and furthermore the stability of Si_2o, Ge_2o vs. the unstable C_20-