Self-assembling of fullerene C<Subscript>60</Subscript> into (C<Subscript>60</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clasters in aromatic solvents

Self-assembling of fullerene C₆₀ into (C₆₀) _n clusters in aromatic solvents was studied. The role of the π-π interactions and dispersion forces in the (C₆₀) _n cluster formation in these media is demonstrated using the data on the solubility of fullerene C₆₀ in these solvents and their ionization potentials and also spectral characteristics of fullerene C₆₀ in the range of 326–340 nm in different solvents.     

Molecular modeling of hydration properties of hydrophobic ions Li<Superscript>+</Superscript>@C<Subscript>60</Subscript> and K<Superscript>+</Superscript>@C<Subscript>60</Subscript>

The Gibbs free energies of solvation (ΔG _s) and the electronic structures of endohedral metallofullerenes M⁺@C₆₀ (M⁺= Li⁺, K⁺) were calculated within the framework of the density functional theory and the polarizable continuum model. In water environment, the equilibrium position of K⁺ is at the center of the fullerene cavity whereas that of Li⁺ is shifted by 0.14 nm toward the fullerene cage. The Li⁺ cation is stabilized by interactions with both the fullerene and solvent. The equilibrium structures of both endohedral metallofullerenes are characterized by very close ΔG _s values. In particular, the calculated ΔG _s values for K⁺@C₆₀ are in the range from −124 to −149 kJ mol⁻¹ depending on the basis set and on the type of the density functional. Molecular dynamics simulations (TIP3P H₂O, OPLS force field, water sphere of radius 1.9 nm) showed that the radial distribution functions of water density around C₆₀ and M⁺@C₆₀ are very similar, whereas orientations of water dipoles around the endohedral metallofullerenes resemble the hydration pattern of isolated metal ions.     

Inertness of C<Subscript>60</Subscript> fullerene toward RO<Subscript>2</Subscript><Superscript>·</Superscript> peroxy radicals

The reactivity of fullerene C₆₀ toward peroxy radicals RO₂ ^· was tested by the chemiluminescence method. A comparison of the influence of C₆₀ and known inhibitors on the kinetics of liquid-phase chemiluminescence (CL) during oxidation of a series of hydrocarbons (ethyl-benzene, cyclohexane, n-dodecane, and oleic acid) shows that the fullerene does not react with the RO₂ ^· radicals. A sharp decrease in the CL intensity observed upon C₆₀ addition is caused by the quenching of CL emitters with fullerene but not by inhibition of hydrocarbon oxidation. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1808–1811, August, 2005.     

Solution ozonolysis of C<Subscript>70</Subscript>: stable products and chemiluminescence

For the first time the total and relative contents of the stable ozonolysis products of fullerene C₇₀ solutions were identified by IR spectroscopy and elemental and chemical analyses. At the 100% conversion of C₇₀ a mixture of products corresponding to the empirical formula C₇₀O_14.3H_0.21 (epoxides: polyketones: polyesters: secondary fullerene ozonides (SFOZ): acids = 1.07: 6: 6: 0.21: 1.02) is formed. The content of polyketones, polyesters, acids, and SFOZ increases during the whole ozonolysis time (1 h). The number of oxygen atoms in epoxides C₇₀O _n (n = 1–4) is lower than that in epoxides C₆₀O _n (n = 1–6) formed by the ozonolysis of fullerene C₆₀. The kinetic curve of accumulation of epoxides C₇₀O _n (n = 1–4) passes through a maximum, which is observed 0.5 min after the beginning of ozonolysis. No epoxides were identified among the products 3.5 min after the ozonolysis. The photoluminescence (PL) (λ_max = 645 and 685 nm) of fullerene polyketones in glassy EtO₂/EtOH solutions frozen at 77 K was observed. This PL is much brighter, than that of polyketones formed upon the ozonolysis of fullerenes C₆₀. For the first time the chemiluminescence (CL) was detected and studied upon the ozonolysis of C₇₀ solutions at 300 K. The CL emitters are excited states of fullerene polyketones. The CL spectrum is partially overlapped with the known CL spectrum appeared upon the ozonolysis of C₆₀ (λ_max = 685 nm) but contains the greater number of maxima (λ_max = 645 and 685 nm), which is related to a lower symmetry of the C₇₀ oxidation products.     

Mass spectrometric determination of the electron affinity of C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>10</Subscript> and C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>12</Subscript> molecules

Knudsen cell mass spectrometry was used to study ion-molecular electron exchange reactions between some trifluoromethyl derivatives of C₆₀ fullerene. Electron affinity values were experimentally determined for C₆₀(CF₃)₁₀ and the S ₆ isomer of C₆₀(CF₃)₁₂ and compared with the results of calculations and the data in the literature.     

Thermodynamic properties of solutions of fullerene C<Subscript>60</Subscript> in mixtures of tetraline with carbon tetrachloride and 1,2-dichlorobenzene

The solubility of fullerene C₆₀ in tetraline-carbon tetrachloride and tetraline-1,2-dichlorobenzene systems in all compositions of the mixed solvent are measured in the temperature range of 298.15–338.15 K. It is found that in a mixture of tetraline with 1,2-dichlorobenzene, the solubility of C₆₀ is considerably higher than in its pure components; in this case, solubility has a maximum in the range of lower temperatures and compositions of the mixture X _trl = 0.3–0.5. It is established that C₆₀ forms crystal solvates with components of the mixed solvents. Enthalpies and temperatures of incongruent melting of the crystal solvates are determined by differential scanning calorimetry.     

Octafluorocyclohexa derivatives of [60]fullerene: C<Subscript>60</Subscript>(C<Subscript>4</Subscript>F<Subscript>8</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 2, 3, 4, and 6)

Fluorocyclohexa adducts C₆₀(C₄F₈) _n were synthesized by high-temperature reaction of fullerene C₆₀ with 1,2-C₂F₄I₂ or 1,4-C₄F₈I₂ in sealed tubes. Their separation by HPLC allowed us to determine molecular structure (X-ray diffraction) of four new compounds C₆(C₄F₈) _n (n = 2, 3, 4, and 6). Structures of isomers C₆₀(C₄F₈) _n were discussed in terms of a concept of consecutive addition of C₄F₈ groups to the fullerene cage.     

Endohedral Complex of Fullerene C<Subscript>60</Subscript> with Tetrahedral N<Subscript>4</Subscript>, N<Subscript>4</Subscript>@C<Subscript>60</Subscript>

B3LYP/6-31G(d) hybrid HF/DFT and BLYP/6-31G(d, p) DFT calculations were carried out to determine the structural and electronic properties of the endohedral complex of C₆₀ with Tetrahedral N₄ (T_d N₄), N₄@C₆₀. It was demonstrated that N₄ was seated in the center of the fullerene cage and the tetrahedral structure of N₄ is remained in the cage. The formation of this complex is endothermic with inclusion energy of 37.92 kcal/mol. N₄ endohedral doping perturbs the molecular orbitals of C₆₀ not so much, the calculated HOMO–LUMO gaps, the electron affinity (EA) and the ionizational potential (IP) of N₄@C₆₀ are similar to that of C₆₀.     

Circular dichroism of optically active organometallic derivatives of fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript>

Palladium and platinum complexes of fulleienes C₆₀ and C₇₀ containing the axially chiral ligand (—)-BITIANP (BITIANP is 2,2’-bis(diphenylphosphino)-3,3’-bi(benzo[b]thiophene)) and pynolidino[60]fullerene bearing a planar chiral organometallic π-complex substituent in the heteiocyclic ring were studied by circular dichroism (CD) spectroscopy.     

A Quantum Chemical Study of C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>, C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Molecules and Fe@C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Endocomplex

(U)PBE0/cc-pVDZ method is used to study the structure of C₆₀Cl₃₀, C₆₀(OH)₃₀ molecules and Fe@C₆₀(OH)₃₀ endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s²2s²2p⁶3s²3p⁶3d^7.24s^0.14p^0.3 electron configuration of iron with spin population of 2.36.     

Benzene Adsorption on C<Subscript>24</Subscript>, Si@C<Subscript>24</Subscript>, Si-Doped C<Subscript>24</Subscript>, and C<Subscript>20</Subscript> Fullerenes

The absorption feasibility of benzene molecule in the C₂₄, Si@C₂₄, Si-doped C₂₄, and C₂₀ fullerenes has been studied based on calculated electronic properties of these fullerenes using Density functional Theory (DFT). It is found that energy of benzene adsorption on C₂₄, Si@C₂₄, and Si-doped C₂₄ fullerenes were in range of –2.93 and –51.19 kJ/mol with little changes in their electronic structure. The results demonstrated that the C₂₄, Si@C₂₄, and Si-doped C₂₄ fullerenes cannot be employed as a chemical adsorbent or sensor for benzene. Silicon doping cannot significantly modify both the electronic properties and benzene adsorption energy of C₂₄ fullerene. On the other hand, C₂₀ fullerene exhibits a high sensitivity, so that the energy gap of the fullerene is changed almost 89.19% after the adsorption process. We concluded that the C₂₀ fullerene can be employed as a reliable material for benzene detection.     

Electron interactions in the (η<Superscript>2</Superscript>-C<Subscript>60</Subscript>)Pd[P(Ph<Subscript>2</Subscript>)C<Subscript>5</Subscript>H<Subscript>4</Subscript>]<Subscript>2</Subscript>Fe complex

The electronic structure of the (η²-C₆₀)Pd[P(Ph₂)C₅H₄]₂Fe complex was calculated by the “hybrid” B3LYP method. Comparison of the experimental X-ray emission C-Kα spectrum and theoretical spectrum of the compound demonstrated that the electron interactions between the C₆₀ core, palladium atom, and organometallic fragment are described correctly in the framework of the quantum chemical method used. The electronic structure of the organometallic fullerene complex can be presented as a set of blocks of orbitals corresponding to different types of chemical bond. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2640–2644, December, 2005.     

The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

Effect of fullerene C<Subscript>60</Subscript> on the structure and mechanical characteristics of polyethylene: Technological aspect

On the basis of the literature data, a retrospective analysis of the thermodynamic characteristics of dissolution of fullerene C₆₀ in a series of single-ring aromatic solvents is presented. The effect of the molecular structure of a solvent on its dissolving capacity with respect to fullerene is studied. The parameter of the boiling temperature of the solvent normalized to its molecular mass is introduced. The correlation of this parameter with the dissolving capacity of the solvent is discussed. Special emphasis is placed on the effect of halogen-containing solvents on the dissolution of fullerene and indirectly on the development of the mechanical characteristics of films prepared from common solutions of fullerene and low-density polyethylene. For comparison, the films prepared from PE melts modified with low concentrations of fullerene are considered. The film structure is studied via X-ray analysis, optical microscopy, AFM, small-angle scattering of linearly polarized light, and DSC. The films with the maximum strength are prepared from solutions in halogen-containing solvents at a concentration of fullerene below 1 wt %. In this case, spherulites are 5–10 times smaller than those in the films cast from solutions in other solvents. In the films cast from common solutions of PE and fullerene in bromobenzene, crystal solvates C₆₀ · 2C₆H₅Br are formed. It seems that the formation of the crystal solvates binds the residual solvent and thus affects the mechanical behavior of the films, thereby eliminating the plasticizing effect of residual bromobenzene. Localization of fullerene in various regions of the supramolecular structure of the films is discussed, and the morphology of the separating regions of the crystal solvate fullerene phase is analyzed.     

Synthesis and electrochemical properties of fullerene-containing C<Subscript>60</Subscript>-acceptor dyads with fluoronitrobenzene and fluoroquinoxaline moieties as substituents

Reactions of fullerene C₆₀ with 4-azido-3-fluoro-1-nitrobenzene and 7-azido-6-fluoroquinoxaline afforded earlier unknown cycloadducts (C₆₀-acceptor dyads), in which the electron affinities of the fullerene spheres are comparable with the affinity of nonmodified C₆₀.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 650–655, March, 2005.     

The standard enthalpy of formation of fullerene chloride C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>

A rotating-bomb calorimeter was used to measure the energy of combustion of crystalline fullerene chloride C₆₀Cl₃₀ · 0.09Cl₂, Δ_c U° = (?24474 ± 135 kJ/mol). The result was used to calculate the standard enthalpy of formation, Δ_f H° (C₆₀Cl₃₀, cr) = 135 ± 135 kJ/mol, and the C-Cl bond energy, 195 ± 5 kJ/mol. The C-X (X = F, F, Cl, and Br) bond energies in fullerene C₆₀ derivatives and other organic compounds are compared.     

Features of the oxidation of C<Subscript>60</Subscript> and C<Subscript>70</Subscript> fullerites as studied by IR spectroscopy

Features of the oxidation of C₆₀ and C₇₀ fullerites were studied by infrared spectroscopy. It was shown that for C₆₀ fullerite, the presence of toluene residue reduces the temperature at which oxidation starts. The form of the toluene (solvate or nonsolvate) is not important. A low-frequency shift in the valence C-O-C vibrations of C₇₀ fullerene due to local steric strains was discovered.     

Generation of fullerenyl radicals and chemiluminescence in the (C<Subscript>60</Subscript>—R<Subscript>3</Subscript>Al)—O<Subscript>2</Subscript> system

Fullerenyl radicals (FR) RC₆₀ ^· and chemiluminescence (CL) are generated in the presence of O₂ in C₆₀—R₃Al (R = Et, Buⁱ) solutions in toluene (T = 298 K). The FR are formed due to the addition of the R^· radical, which is an intermediate of R₃Al autooxidation, to C₆₀. Mass spectroscopy and HPLC were used to identify Et_nC₆₀H_m (n, m = 1–6), Et_pC₆₀ (p = 2–6), and dimer EtC₆₀C₆₀Et as stable products of FR transformations. As found by ESR, the EtC₆₀ ^· radical (g = 2.0037) is also generated by photolysis of solutions obtained after interaction in the (C₆₀— R₃Al)—O₂ system. In the presence of dioxygen, the FR is not oxidized but yields complexes with O₂, which appear as broadening of the ESR signals. Chemiluminescence arising in the (C₆₀—R₃Al)—O₂ system is much brighter (I _max = 1.86·10⁸ photon s⁻¹ mL⁻¹) than the known background CL (I _max = 6.0·10⁶ photon s⁻¹ mL⁻¹) for the autooxidation of R₃Al and is localized in a longer-wavelength spectral region (λ_max = 617 and 664 nm). This CL is generated as a result of energy transfer from the primary emitter ³CH₃CHO* to the products of FR transformation: R_nC₆₀H_m, R_pC₆₀, and EtC₆₀C₆₀Et. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 205–213, February, 2007.     

Structure,energy, and spin characteristics of La@C<Subscript>60</Subscript>-Lu@C<Subscript>60</Subscript> lanthanide endofullerenes

Calculations of the equilibrium geometric and electronic structure of lanthanide endofullerenes are presented. Two types of the Ln@C₆₀ structure are found. For endofullerenes of the first type (La@C₆₀-Dy@C₆₀), the stable position of the lanthanide atom is achieved at a distance of 0.67R from the center of fullerene (R is the fullerene radius); in endofullerenes of the second type (Ho@C₆₀-Lu@C₆₀), the character of the interaction between the lanthanide atom and fullerene changes because of the transfer of unpaired electrons from the corresponding atom to fullerene. It is found that in endofullerenes of the second type, metal atom mobility increases, and two minima of the potential energy appear, which corresponds to the Ln position in the center and at a distance of 0.5R from the center. Based on the obtained spin density distribution for La@C₆₀-Lu@C₆₀ endofullerenes, we conclude that there is spin leakage.     

Synthesis of fullerene epoxide (C<Subscript>60</Subscript>O) by oxidation of fullerene C<Subscript>60</Subscript> with oxygen catalyzed by Mn(III), Ni(II), and Co(II) acetylacetonates

A procedure has been developed for the synthesis of fullerene monoepoxide C₆₀O via liquid-phase oxidation of fullerene C₆₀ in the presence of accessible catalysts [(Mn(acac)₃, Ni(acac)₂, and Co(acac)₂].