Synthesis and EPR investigation of nitroxyl derivatives of fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript>

Nitroxide derivatives of C₆₀ and C₇₀ were obtained by [3+2] cycloaddition of 4-(4-azidophenyl)-2,2,5,5-tetramethyl-3-oxy-2,5-dihydroimidazol-1-oxyl to fullerenes. The products were isolated by TLC and studied by EPR and optical spectroscopy. Molecular rotation of the adducts was shown to slow down on successive addition of the nitroxides, rotational correlation times depending nearly linearly on the number of the nitroxides added. Investigation of photochemical stability of nitroxide derivatives of C₆₀ and C₇₀ in benzene-ethanol medium reveal that the dissolved oxygen quenches efficiently the excitation of nitroxide (λ = 250–400 nm). In the absence of oxygen photoexcitation converts nitroxides to diamagnetic products, presumably, hydroxylamines formed through the interaction with the solvent.     

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.     

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.     

The structural-phase state of C<Subscript>60</Subscript>-C<Subscript>70</Subscript> fullerene mixtures

The structural and phase state of the C₆₀-C₇₀ system at various C₆₀/C₇₀ ratios in mixtures obtained by the vaporization of solutions in toluene at ∼98°C was studied by X-ray structure analysis, differential scanning calorimetry, and infrared spectroscopy. Solid solutions based on the face-centered cubic packing of C₆₀ are not formed in the C₆₀-C₇₀ system at C₇₀ contents from 0.5 to 50 wt %. The hexagonal close packing of a solid solution of C₆₀ in C₇₀ can be formed as a result of the thermally activated decomposition of the ternary crystal solvate in the C₆₀-C₇₀-C₆H₅CH₃ system. The structural state of multiphase mixtures formed under conditions far from equilibrium is characterized by a high degree of structure imperfection and greater ability to undergo oxidation compared with C₆₀ and C₇₀.     

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.     

Aqueous dispersions of C<Subscript>60</Subscript> fullerene

Stable aqueous colloidal dispersions of C₆₀ fullerene are prepared. A solvatochromic effect is revealed upon the addition of C₆₀ solution in chlorobenzene to a water-acetone mixture.     

Synthesis of fullerene C<Subscript>60</Subscript> monoadducts. Cyclopropanation of C<Subscript>60</Subscript> with sulfonium ylides

3′H-Cyclopropa[1,9](C₆₀-I_h)[5,6]fullerene-3′-carboxylic acid can be synthesized in a good yield by cyclopropanation of fullerene C₆₀ with 2-(dimethyl-λ⁴-sulfanylidene)acetates provided that the ester residue is readily hydrolyzable in acid medium.     

Synthesis and structures of C<Subscript>60</Subscript> fullerene chlorides

Systematic study of chlorination of fullerene C₆₀ with inorganic chlorides SbCl₅, VCl₄, MoCl₅, and KICl₄ was carried out. Higher chlorofullerenes, viz., T _h -C₆₀Cl₂₄, C₆₀Cl₂₈, C ₂-C₆₀Cl₃₀, and D _3d -C₆₀Cl₃₀, can be prepared depending on the temperature and time of chlorination. The molecular and crystal structures of C₆₀Cl₂₄⋅VOCl₃, C₆₀Cl₃₀⋅2CS₂, and C₆₀Cl₃₀O_1.22 were determined by single-crystal X-ray diffraction. Fullerenes C₆₀Cl₂₈ and C ₂-C₆₀Cl₃₀ were shown to be only kinetically stable, whereas D _3d -C₆₀Cl₃₀ is a thermodynamically stable product. Transformations of less chlorinated fullerenes into more chlorinated products are accompanied by substantial changes in the addition patterns. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1608–1618, July, 2005.     

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.     

Synthesis and structure of allylated derivatives of fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript>

New chromatographically pure monoand hexamethanofullerenes C₆₀ and C₇₀ containing active allylic groups were synthesized by Bingel—Hirsch reaction. These compounds are promising for the studies of biological activity, as well as for obtaining on their basis new fullerenecontaining materials. The purity and composition of the synthesized compounds were confirmed by MALDI-TOF mass spectrometry and HPLC, their structure was established by ¹H and ¹³C NMR spectroscopy and X-ray diffraction.     

Sorption of light fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript> on NORIT-AZO carbon

Sorption of fullerenes C₆₀ and C₇₀ from o-xylene, toluene, and dichlorobenzene solutions on NORIT-AZO carbons was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1638–1642.Original Russian Text Copyright © 2004 by Semenov, Seregin, Arapov, Charykov.     

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.     

Reactivity of fullerene C<Subscript>60</Subscript>

The results of a quantum-chemical study of the reactivity of fullerene C₆₀ in such reactions as polymerization (dimerization), cycloaddition, addition of valence-saturated molecules are presented. The mechanisms of these reactions are also discussed.     

Enhanced radical scavenging activity of polyhydroxylated C<Subscript>60</Subscript> functionalized cellulose nanocrystals

A first demonstration of conjugated polyhydroxylated fullerene (C₆₀(OH)₃₀) on the surface of cellulose nanocrystals (CNC)s is reported. These nanohybrids display favourable antioxidant performance and are an attractive alternative to derivatized fullerene nanocages reported previously. UV–Vis measurements indicated that the C₆₀(OH)₃₀-CNC system scavenged 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals to a greater degree than C₆₀(OH)₃₀ alone, due to the nucleation of C₆₀(OH)₃₀ on the surface of CNC and high colloidal stability of the engineered nanohybrid. A mechanism for the 2-stage process of the radical reaction with C₆₀(OH)₃₀-CNC is proposed, and modelled by pseudo-first order kinetics. Successful grafting of C₆₀(OH)₃₀ on CNC was confirmed by FTIR, while TEM revealed the morphology of the system with a grafting degree of 20.8 % C₆₀(OH)₃₀. Zeta potential measurements of C₆₀(OH)₃₀-CNC in aqueous solution showed a high stability in the pH range 4.0-8.0, indicating functionality of the CNC based antioxidant system as a biocompatible and sustainable protocol with potential for use in personal care applications.     

Electroactive Polymerization Behaviors of Fused-Pentagon Chlorofullerenes: <Superscript>#1809</Superscript>C<Subscript>60</Subscript>Cl<Subscript>8</Subscript> and <Superscript>#271</Superscript>C<Subscript>50</Subscript>Cl<Subscript>10</Subscript>

The fullerenes that violate isolated pentagon rule (IPR) have unusual electronic properties resulting from their fused-pentagon structures. Numerous non-IPR fullerenes have now been captured by chlorination, affording opportunity to go insight into the properties involved in non-IPR fullerenes in the forms of chlorofullerenes (CFs). Here cyclic voltammetry (CV) is employed to probe the electrochemical properties of non-IPR ^#1809C₆₀Cl₈ in comparison with those of ^#271C₅₀Cl₁₀. Differing from IPR-satisfying CFs such as C₆₀Cl₈ and C₆₀Cl₁₀ (referring to I _h-symmetric C₆₀), the two non-IPR CFs exhibit divergent electroactive polymerization characters. In addition, the electrocatalytic effect of ferrocene that is otherwise employed as internal reference has been shown in the CV process of CFs.     

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.     

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.     

The thermodynamic properties of fullerene hydrides C<Subscript>60</Subscript>H<Subscript>2<Emphasis Type="Italic">n</Emphasis></Subscript>

The equilibrium geometric parameters and normal vibration frequencies of the C₆₀H₂, C₆₀H₁₈, and C₆₀H₆₀ molecules were determined using density functional theory at the B3LYP/6-31G* level. The results were used to calculate the thermodynamic properties of the substances in the ideal gas state. The heat capacity of crystalline hydrofullerenes was modeled and the enthalpies of their sublimation estimated. The thermodynamic parameters of the hydrogenation of fullerene C₆₀ were analyzed.     

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.