Generalized topological efficiency – case study with C84 fullerene

Abstract

A pure topological mechanism able to explain fullerenes stability is presented here. The non-trivial case of the C₈₄ fullerene isomers with isolated Pentagons Is in fact analyzed. This original computational approach is based on the generalization of the topological efficiency potentials which may be used to study all types of carbon allotropes.     

A study on the aromaticity and kinetic stability of fullerene C38 isomers and their molecular ions

The aromaticity of the fullerene C₃₈ isomers and their molecular ions is examined by the topological resonance energy (TRE) method. The aromaticity order obtained by the TRE method is compared with relative energies found in DFT calculation results reported in literature. It is found that all C₃₈ isomers exhibit antiaromaticity when in the neutral state. However, they are highly aromatic in the hexaanionic states. The minimum bond resonance energy (min BRE) method is utilized to estimate the kinetically stability of the C₃₈ isomers and their molecular ions. According to the min BRE method, C₃₈ isomers are only have kinetic stability in penta- and hexavalent molecular anionic states.     

GENERATION OF HIGHER FULLERENES FROM LASER ABLATION OF CARBYNE AND C60 PHOTOPOLYMER ASTROCHEMICAL IMPLICATIONS

ABSTRACT

Laser ablation of targets of carbonaceous matter containing carbyne nanodomains (the sp hybridised carbon chains) or targets of C₆₀ photopolymer produced carbon clusters which have been detected by FT-ICR (Fourier-Transform Ion Cyclotron Resonance) mass spectrometer. When the carbonaceous matter containing carbyne has been employed as laser target, no C₆₀ has been generated but only fullerene cages from C₇₄ up to C₁₂₄. Larger cages were also obtained but with odd number. Starting from C₆₀ photopolymer, laser ablation regenerates free C₆₀ and creates a sequence of C₆₀ superior homologues all possessing even number and each member of the series is separated from the preceding and the following member by the loss or by the addition respectively of a C₂ unit. Fullerenes up to C₁₆₂ have been recorded. The implications about the presence of free C₆₀ fullerene in the interstellar and circumstellar space, its formation from carbyne chains and its stability towards its photopolymerization tendency and its regeneration from the photopolymer together with its superior homologues have been discussed thoroughly in the present paper.     

B3LYP/6-31G∗//SAM1 Calculations of C36 Fullerene and quasi-Fullerene Cages

Abstract

The recently isolated fullerene C₃₆ is computed by the SAM1 method with energetics refined at the B3LYP/6-31G? level. Twelve low-energy cages are considered in detail, exhibiting both fullerene (pentagons and hexagons) and quasi-fullerene (also squares and heptagons) pattern. In contrast to other fullerene systems, the SAM1 and B3LYP/6-31G? methods do produce somewhat different energetics. Consequently, the equilibrium isomeric composition at high temperatures is different, too. In the best affordable B3LYP/6-31G? approach the fullerene cage with the topological D _6d symmetry represents the most populated species at high temperatures. Hence, an agreement with the solid-state NMR experiment is achieved at the B3LYP/6-31G? theoretical level.     

Geometry and energetics of Si60 isomers

The novel electronic, optical and super-conducting properties exhibited by C₆₀ and its assembled materials have greatly stimulated the scientists all over the world racing to study Si₆₀. In this paper we performed an extensive search from eighteen isomers including cages, wires, and stuffed structures of Si. It is found that the fullerene cage is not stable, and the tricapped-trigonal-prism unit is not the structural unit for Si₆₀. While the spherical compact structure is the most stable energetically, in agreement with experiments which suggested a transition from the elongated geometry to a more spherical one for the medium sized Si clusters [J. Chem. Phys. 111 (1999) 7865, J. Chem. Phys. 117 (2002) 3219].     

Geometry and energetics of Si60 isomers

The novel electronic, optical and super-conducting properties exhibited by C₆₀ and its assembled materials have greatly stimulated the scientists all over the world racing to study Si₆₀. In this paper we performed an extensive search from eighteen isomers including cages, wires, and stuffed structures of Si. It is found that the fullerene cage is not stable, and the tricapped-trigonal-prism unit is not the structural unit for Si₆₀. While the spherical compact structure is the most stable energetically, in agreement with experiments which suggested a transition from the elongated geometry to a more spherical one for the medium sized Si clusters [J. Chem. Phys. 111 (1999) 7865, J. Chem. Phys. 117 (2002) 3219].     

Molecular structures of the open-shell IPR isomers of fullerene C90

Fifteen open-shell isomers off the forty six IPR isomers of fullerene C₉₀ were found and investigated: 5 (C_s), 7 (C₁), 9 (C₁), 10 (C_s), 11 (C₁), 20 (C₁), 21 (C₁), 22 (C₁), 23 (C₂), 24 (C₁), 25 (C_2v), 41 (C₂), 42 (C₂), 43 (C₂), and 44 (C₂). According to developed by us approach the positions of single, double, and delocalized π-bonds in the molecules of these isomers are shown for the first time. The obtained results of electronic and geometrical structures are fully supported by DFT method with the B3LYP functional at the 6-31G and 6-31G* levels. Molecules of these open-shell isomers contain different radical substructures (mainly the phenalenyl-radical substructures), they should be unstable and could not be obtained as empty molecules. Nevertheless, there is a possibility of obtaining them in polymeric forms or as endohedral or exohedral derivatives.     

Modeling the structure of fulleranes and their endohedral complexes involving small molecules with nontrivial topological properties

'In' and 'out' isomers of perhydrogenated fullerenes and endohedral fullerene complexes have only recently been incorporated into the realm of topological chemistry. The 'in' isomers are, until now, purely hypothetical while for the latter group mostly studied are the complexes with metal ions that can be obtained during the fullerenes manufacturing. Much more difficult to obtain are the complexes with small molecules buried inside fullerene cages produced by laborious synthesis involving opening the cage, inserting the guest into it, and closing the cage chemically. This complicated procedure has only recently been accomplished for a hydrogen molecule put in the C60. Two H2 molecules inside the opened C70 cage and H2O in the opened C60 have been also reported recently. Model calculations, when carefully applied, allow one to predict the possibility of obtaining endohedral fullerene complexes with small molecules and 'in' isomers of perhydrogenated fullerenes. However, such systems are too large to be reliably handled by quantum calculations. Interestingly, such a simple method as molecular mechanics seems much more trustworthy.     

A MODEL STUDY OF NARROW NANOTUBES RELATED TO C36, C32, C20, AND C16: SEMIEMPIRICAL AND NONEMPIRICAL TREATMENTS

ABSTRACT

Very recently, narrow nanotubes have been observed with diameters of 5 or even 4?Å. In this report we perform calculations of narrow model nanotubes capped by fragments of D _2d and D _6h C₃₆ fullerene cages or by fragments of C₃₂ and C₁₆ quasi-fullerene cages with two four-membered rings, or finally by a fragment of dodecahedral C₂₀. The computations can reproduce the observed diameters of the narrow nanotubes. The results also indicate that fragments of C₃₂, used as caps instead of C₃₆, can lead to quite competitive energetics. Thus, a novel possibility that some of the narrow nanotubes can contain four-membered rings at their tips is suggested.     

Crystal Structure of C60 and C70 Compounds

Abstract

Fullerene intercalated compounds are the most intensively examined molecular materials to exhibit superconducting, ferromagnetic, optical non-linear and other properties. the fullerene C₆₀ or C₇₀ serve usually as electron acceptors in these materials. Although the electron acceptor properties of the fullerene are similar to those of the weak organic acceptors, the fullerene forms various C₆₀-based materials, namely clathrates, charge-transfer complexes and weak, molecular complexes. the search for cation species for fullerene-based materials is one of the routes towards progress in the design of materials with interesting physical properties.

Physical properties of the fullerene-derived molecular compounds are determined mainly by their crystal structure packing. Relatively large cavities in the fullerene solid can easily accommodate small units like solvent molecules or electron-donor organic compounds. An intercalation with these species is usually accompanied either by a lowering in crystal symmetry or by a change in the stacking arrangement of the C₆₀ spheres. These factors influence the interactions between fullerene (host) and an organic molecule (guest). Charge transfer between the electron donor molecule and the fullerene is usually weak and is hindered by unfavourable steric factors; it does not correlate with the ionization potential of the donor.

In this paper we present characteristic structures of one-, two-, and three-component fullerene compounds or else the structures of fullerene clathrates, neutral (van der Waals) complexes and ionic charge-transfer complexes. One can conclude that the stability and properties of the fullerene-based derivatives are defined by the steric compatibility between the three-dimensional donor and the spherical or elongated fullerene.     

Contact stability of C60 molecules on pure and doped (100) tungsten surface

The influence of the metal surface doping on the contact stability of adsorbed fullerene molecules at room temperature was observed for the first time. The C₆₀ fullerene molecules decompose at room temperature both on a pure (100)W surface and on a tungsten surface containing carbide (WC), while the presence of a surface silicide of the same stoichiometry (WSi) produces passivation of the metal surface, thus preventing the fullerene molecules from decomposition.     

Synthesis of fullerene nanowhiskers using the liquid–liquid interfacial precipitation method and their mechanical,electrical and superconducting properties

Abstract

Fullerene nanowhiskers (FNWs) are thin crystalline fibers composed of fullerene molecules, including C₆₀, C₇₀, endohedral, or functionalized fullerenes. FNWs display n-type semiconducting behavior and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Alkali metal-doped C₆₀ (fullerene) nanowhiskers (C₆₀NWs) exhibit superconducting behavior. Potassium-doped C₆₀NWs have realized the highest superconducting volume fraction of the alkali metal-doped C₆₀ crystals and display a high critical current density (J_c) under a high magnetic field of 50 kOe. The growth control of FNWs is important for their success in practical applications. This paper reviews recent FNWs research focusing on their mechanical, electrical and superconducting properties and growth mechanisms in the liquid–liquid interfacial precipitation method.     

First synthesis of a new fullerene oximes bis(9-[hydroxo]-1-[1′-hydroxymino-2′-oxo-2′-alkyl-ethyl])1,9-dihydro-[C60-Ih][5,6]fullerenes via reaction of C60 with ketones and NaNO2 promoted by HCl

A mixture of cis-2 and cis-3 isomers of new fullerene derivatives bis(9-[hydroxo]-1-[1′-hydroxymino-2′-oxo-2′-alkyl-ethyl])-1,9-dihydro-[C₆₀-I_h][5,6]fullerenes have been selectively synthesized with high yields at the reaction of C₆₀ fullerene with ketones Me₂CO, EtMeCO, i-PrMeCO, PhMeCO in the presence of NaNO₂ and HCl.     

Eu@C86 isomers: Calculated relative populations

Abstract

Relative populations of four energy-lowest IPR (isolated-pentagon-rule) isomers of Eu@C₈₆ are computed using the Gibbs energy based on characteristics from density functional theory calculations (M06-2X/3-21G?～?SDD entropy term, M06-2X/6-31G*～SDD or B2PLYP(D)/6-31G*～SDD energetics). The calculations confirm that the recently isolated Eu@C₁(7)-C₈₆ species is a major isomer in a relevant temperature region. Relationship to the empty C₈₆ cages is discussed, too.     

Synthesis of fullerene nanowhiskers using the liquid–liquid interfacial precipitation method and their mechanical,electrical and superconducting properties

Fullerene nanowhiskers (FNWs) are thin crystalline fibers composed of fullerene molecules, including C₆₀, C₇₀, endohedral, or functionalized fullerenes. FNWs display n-type semiconducting behavior and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Alkali metal-doped C₆₀ (fullerene) nanowhiskers (C₆₀NWs) exhibit superconducting behavior. Potassium-doped C₆₀NWs have realized the highest superconducting volume fraction of the alkali metal-doped C₆₀ crystals and display a high critical current density (J_c) under a high magnetic field of 50 kOe. The growth control of FNWs is important for their success in practical applications. This paper reviews recent FNWs research focusing on their mechanical, electrical and superconducting properties and growth mechanisms in the liquid–liquid interfacial precipitation method.     

CHROMATOGRAPHIC PURIFICATION OF Kr@C60

Unusual compounds have been reported to form by the incorporation of atoms into fullerene cages. The compounds in which a noble gas atom is trapped into a C₆₀ cage are very stable and only van der Waals interactions occur between the noble gas and the fullerene cage. The study of these compounds requires efficient chromatographic (or other) separations. We performed the isolation of Kr@C₆₀ and a study of its chromatographic separations on several HPLC columns using toluene : hexane mixtures as solvent. We found that the separation factor is small (1.09 to 1.12) with the highest separation factor on a Buckyprep column.     

Novel Fullerene Containing Liquid Crystalline Dendrimers and Hemi‐dendrimers: Synthesis and Characterization

Abstract

Novel fullerene C₆₀ containing liquid crystalline dendrimers and hemi‐dendrimers have been characterized by the method of electro‐optical Kerr effect and determination of the permanent dipole moment, sensitive to the molecular polar ordering and anisotropy of polarizability, and by hydrodynamic methods in solution. An influence of the covalently bonded fullerene on the polarity, electro‐optical, and viscometric properties of fullerene derivatives have been detected, analyzed, and concluded that fullerene produces a change in the original ordering in dendritic molecules, which mainly resulted in correction of the shape asymmetry of these molecules as a whole.     

A STUDY ON THE THERMAL STABILITY TO 1000°C OF VARIOUS CARBON ALLOTROPES AND CARBONACEOUS MATTER BOTH UNDER NITROGEN AND IN AIR

ABSTRACT

The thermal behavior of graphite, C₆₀ fullerene, fullerene black (carbon soot containing fullerenes), extracted fullerene black and diamond has been analyzed to 1000°C by TGA–DTA (thermogravimetric analysis and differential thermal analysis) under a nitrogen flow at a heating rate of 20°C/min. Very small weight losses have been recorded in the case of graphite and diamond. Furthermore no diamond graphitization has been observed. The sublimation of pure C₆₀ and the fullerene fraction of fullerene black (both pristine and extracted) has been observed and discussed.

The combustion reaction in air flow of graphite, C₆₀ and C₇₀ fullerenes, fullerene black (both unextracted and extracted), carbon nanotubes and diamond has been studied by TGA–DTA at a heating rate of 20°C/min. C₇₀ fullerene and fullerene black have been found to be the most reactive carbon materials with O₂. The role played by C₇₀ in the degradation of fullerites has been discussed. Among the carbon materials examined, the best resistance to O₂ attack has been shown by diamond and carbon nanotubes. The behavior of graphite is intermediate between diamond and fullerene blacks. The behavior of C₆₀ fullerene appears closer to that of graphite although it appears to be more reactive with O₂. Samples of graphite and carbon blacks N375 and N234 have been studied by TGA–DTA in air flow before and after a radiation treatment with neutrons or γ radiation. The effect of the radiation damage in the combustion reaction of these carbon materials has been discussed.     

Thin fullerene-containing films synthesized by ion beam sputtering of fullerene mixtures with doping additives in vacuum

A new approach to the synthesis of films containing fullerenes and doping elements is described. It is suggested that a cluster mechanism of the target sputtering by accelerated ions makes possible the deposition of fullerenes on a substrate with a certain probability for dopant atoms being introduced into the cavities of fullerene molecules and a higher probability of their occurrence between fullerene molecules. The proposed method has been experimentally implemented by using an Ar⁺ ion beam to sputter C₆₀/C₇₀ fullerene mixtures (synthesized in a plasmachemical reactor at a pressure of 10⁵ Pa) pressed into disk targets with a doping element (Fe, Na, B, Gd, or Se). The ion beam sputtering of dopant-containing fullerene mixtures in a vacuum of ～10^?2 Pa allowed micron-thick films containing C₆₀ and C₇₀ fullerenes and the corresponding dopant element (Fe, Na, B, Gd, or Se) to be grown on quartz substrates.     

Synthesis and characterization of higher fullerene (C84) in dc arc discharge using Cu as a catalyst

The synthesis of fullerenes was carried out using dc arc discharge technique. The separation and identification of higher fullerene C₈₄ was done by high performance liquid chromatography (HPLC). The raw soot collected from the high temperature region was dissolved in toluene and then toluene-extracted soot dissolved in n-hexane and kept in laboratory environment for more than one month. The peaks of C₆₀ and C₇₀ along with C₈₄ were observed. The existence of C₈₄ was confirmed by using linear regression between capacity factor log [k′] and the carbon number.