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.     

Thermodynamic properties of graphite-like nanostructures prepared by thermobaric treatment of fullerite C60

Temperature dependences of the heat capacities of disordered graphite-like nanostructures prepared by the thermobaric treatment of fullerite C₆₀ (p = 2 and 8 GPa, T = 1373 K) were measured in the temperature ranges from 7 to 360 K in an adiabatic vacuum calorimeter and from 330 to 650 K in a differential scanning calorimeter. At T < 50 K, the dependences obtained were analyzed using the Debye theory of the heat capacity of solids and its multifractal version. The fractal dimensions D were determined and some conclusions on the heterodynamic character of the structures studied were made. The 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) were calculated in the temperature range from T → 0 to 610 (650) K. The thermodynamic properties of the graphite-like nanostructures studied and some carbon allotropes were compared. The standard entropies of formation Δ_f S ^o of the graphite nanostructures studied and diamond were calculated along with the standard entropies of the reactions of their synthesis from the face-centered cubic phase of fullerite C₆₀ and their interconversions at T = 298.15 K. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1940–1945, September, 2008.     

Thermodynamic properties of crystalline polymeric C60 phases in the temperature region from O → 0 to 340 E

The temperature dependences of the heat capacity C _p° = f(T) were studied in an adiabatic vacuum calorimeter for the orthorhombic, tetragonal, and rhombohedral polymeric C₆₀ phases in the 7—340 K temperature interval with an error of 0.2%. Comparative analysis of C _p° of these phases formed by stacking of one-dimensional and two types of two-dimensional polyfullerenes C₆₀, was performed, and their fractal dimensionalities D were determined for temperatures below 50 K. The thermodynamic functions of the crystalline polymeric C₆₀ phases were calculated in the temperature region from O 0 to 340 K: C _p°(T), H°(T) — H°(0), S°(T) — S°(0), and G°(T) — H°(0). Assuming that S°(0) = 0, the standard entropies of formation _f S° of these phases from graphite at T = 298.15 K and standard pressure were calculated. In addition, the entropies of transformation of the initial face-centered cubic phase of fullerite C₆₀ in the crystalline polymeric C₆₀ phases and entropies of their interconversions under the same conditions were estimated. The thermodynamic characteristics of the polymeric C₆₀ phases were reviewed.     

Fullerene C<Subscript>60</Subscript> as a superefficient quencher of singlet exited states of polycyclic aromatic hydrocarbons

Quenching of fluorescence of polycyclic aromatic hydrocarbons (PAH), namely, naphthalene, anthracene, 9,10-diphenylanthracene, 9,10-dibromoanthracene by C₆₀ fullerene in ethylbenzene at 293 K was found and investigated. The phenomenon is characterized by abnormally high values of bimolecular rate constants for quenching (k _bim = (0.18–6.78)·10¹² L mol⁻¹ s⁻¹) determined from the Stern—Volmer dependence of the PAH fluorescence intensity on the C₆₀ concentration and occurs through the inductive-resonance (dominant channel) and exchange-resonance (minor channel) energy transfer from ¹PAH* to C₆₀. The overlap integrals of the PAH fluorescence spectra with the C₆₀ absorption spectrum and the critical energy transfer distances were calculated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 432–436, March, 2007.     

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.     

Formation and properties of the Fe<Subscript>8</Subscript>V<Subscript>10</Subscript>W<Subscript>16–x</Subscript>Mo<Subscript>x</Subscript>O<Subscript>85</Subscript> type solid solution

Solid solution phases of a formula Fe₈V₁₀W_16–xMo_xO₈₅ where 0≤x≤4, have been obtained, possessing a structure of the compound Fe₈V₁₀W₁₆O₈₅. It was found on the base of XRD and DTA investigations that these solution phases melted incongruently, with increasing the value of x, in the temperature range from 1108 (x=0) to 1083 K (x=4) depositing Fe₂WO₆ and WO₃. The increase of the Mo⁶⁺ ions content in the crystal lattice of Fe₈V₁₀W₁₆O₈₅ causes the lattice parameters a=b contraction with cbeing almost constant. IR spectra of the Fe₈V₁₀W_16–xMo_xO₈₅ solid solution phases have been recorded.     

Doping of fullerite with molecular oxygen at low temperature and pressure

Two methods are described for doping of fullerite C₆₀ with molecular oxygen at a pressure of ∼104 Pa and at temperature 20–30 °C. It was found by mass spectrometry using oxygen ¹⁸O as dopant that a portion of molecular oxygen absorbed by the pre-decontaminated fullerite (first method) is removed as CO and CO₂ at the heating temperature ≤200 °C. Doping during fullerite precipitation from the liquid phase (second method) makes it possible to prepare samples with the oxygen content ≥1.2 at.%. The fullerite doped with oxygen to this level is diamagnetic. The paramagnetic properties of an O₂ molecule disappear when O₂ is incorporated into the fullerene lattice. This is interpreted on the basis of quantum chemical calculations as a sequence of equilibrium formation of the adduct C₆₀O₂. Calculations showed that the subsequent chemical transformation of C₆₀O₂ resulting in the O-O bond cleavage is energetically favorable, enabling prerequisites for the formation of products of incomplete (CO) and deep (CO₂) oxidation of fullerene under mild conditions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 662–671, April, 2006     

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.     

Preparation and study of hydrides of fullerenes C60 and C70

Fullerene hydrides were prepared by hydrogenation of fullerences C₆₀ and C₇₀ using proton transfer from 9,10-dihydroanthracene to fullerene and were studied by mass spectrometry (electron impact, field desorption), IR, UV, and¹H and¹³C NMR spectroscopy. The main product of the hydrogenation of C₆₀ is C₆₀H₃₆, which is sufficiently stable. Hydrogenation of fullerene C₇₀ gives a series of polyhydrides C₇₀H _n (n=36–46), and the main product is C₇₀H₃₆. The dehydrogenation of C₆₀H₃₆ by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone is not quantitative and results in the formation of fullerene derivatives along with C₆₀. The comparison of the IR and¹H and¹³C NMR spectral data for solid C₆₀H₃₆ with the theoretical calculations suggests that the fullerene hydride has aT-symmetric structure and contains four isolated benzenoid rings located at tetrahedral positions on the surface of the closed skeleton of the molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 4, pp. 671–678, April, 1997.     

Investigation of phase interactions in C<Subscript>60</Subscript> fullerite films during gas phase metal deposition

Fullerite films covered with d-metal layers were obtained. The metal deposited over fullerite was shown to diffuse substantially into the films. The prepared heterophase film structures M/C₆₀ were studied by X-ray diffraction and vibrational spectroscopy. It is established that the interaction between metal and fullerite phases gives rise to chemical bonds M—C₆₀. It results in a partial polymerization of fullerite. Samples of metal-impregnated fullerite films exhibit semiconducting properties.     

Redox-induced hydrogen transfer from hydrofullerene C60H36 to fullerene C60

The possibility of hydrogen transfer from hydrofullerene C₆₀H₃₆ to electrogenerated radical anion C₆₀ ^.− or dianion C₆₀ ²⁻ in propylene carbonate-toluence (3∶2, v/v) was demonstrated by cyclic voltammetry. The process affords C₆₀H₂ as the product. The reaction found is the typical redox-induced process. Translated fromIzvestiya Akodemii Nauk. Seriya Khimicheskaya, No. 6, pp. 1136–1139, June, 1998.     

Aqueous sol–gel processing of precursor oxides for ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript> synthesis

This paper describes the synthesis of ZrW₂O₈ by the use of an aqueous citrate-gel method in order to prepare a fine, pure and homogeneous oxide mixture suitable for ceramic processing. The thermal expansion coefficient thus obtained for α-ZrW₂O₈ is −10.6 × 10⁻⁶ °C⁻¹ (50–125 °C) whereas for the β-ZrW₂O₈ a value of −3.2 × 10⁻⁶ °C⁻¹ (200–300 °C) is obtained. The advantages of the use of a sol–gel method is expressed in the very homogeneous end-products. The paper describes crystallographic data, morphological structure and the thermal expansion properties of the ZrW₂O₈ material. Moreover, photoluminescence and photochromic properties specific to the precursor gel are described and analyzed. These effects support our views that the precursors show homogeneity up to nanometer level.     

Effect of high-pressure high-temperature treatment on the structure of a hexagonal modification of fullerite C<Subscript>60</Subscript>

Powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and molecular dynamics have been employed to investigate structural transformations in hexagonal and cubic modifications of fullerite C₆₀ after the action of high pressure (4 GPa) within the temperature range 20–1450°C. It has been found that fullerene molecules polymerize to afford polymer structures only in the case of face-centered cubic samples. Under the effect of high pressure and temperature, fullerite C₆₀ with a hexagonal close-packed structure is initially transformed into the cubic modification and, then, forms polymerized structures, which, during an increase in the treatment temperature, become less stable and ordered than the same polymerized structures obtained directly from cubic fullerite C₆₀. X-ray photoelectron spectroscopy measurements suggest deformation of the cages of fullerene molecules in the polymerized structures.     

Fullerene complexes with divalent metal dithiocarbamates: structures,magnetic properties,and photoconductivity

A series of complexes of fullerenes C₆₀ and C₇₀ with metal dithiocarbamates {M^II(R₂dtc)₂}·C_m (m = 60 or 70) and metal dithiocarbamates coordinated to nitrogen-containing ligands (L), {M^II(R₂dtc)₂)_x·L}·C₆₀ (x = 1 or 2), where M = Cu, Zn, Cd, Hg, Mn, or Fe, R = Me, Et, Prⁿ, Prⁱ, or Buⁿ, L is 1,4-diazabicyclo[2.2.2]octane (DABCO), N,N′-dimethylpiperazine, or hexamethylenetetramine, were synthesized. The shape of dithiocarbamate molecules is sterically compatible with the spherical shape of C₆₀, resulting in an efficient interaction between their π systems. The resulting compounds are characterized by a layered or three-dimensional packing of the fullerene molecules. In the C₆₀ complexes, iron(II) and manganese(II) dithiocarbamates exist in the high-spin states (S = 2 and 5/2). The magnetic susceptibility of {M^II(Et₂dtc)₂}₂·C_m (M = Fe or Mn, m = 60 or 70) in the temperature range of 200–300 K is described by the Curie-Weiss law with Θ = −250 and −96 K and with maxima at 110 and 46 K, respectively, which is indicative of a strong antiferromagnetic spin coupling between M^II. The Weiss constants for the [{M^II(Et₂dtc)₂}₂·DABCO]·C₆₀·(DABCO)₂ complexes (M = Fe or Mn) are 1.7 and 0.3 K, respectively. The magnetic moments of the complexes containing Fe and Mn dithiocarbamates slightly increase at temperatures below 50 and 35 K, respectively, which is evidence of the ferromagnetic spin coupling between M^II in {M^II(Et₂dtc)₂}₂·DABCO. Single crystals of the complexes exhibit low dark conductivity (10⁻¹⁰–10⁻¹¹ S cm⁻¹). The visible light irradiation of these crystals leads to an increase in the photocurrent by two–three orders of magnitude. The photogeneration of free charge carriers in the complexes occurs both due to the photoexcitation of metal dithiocarbamate (Cu^II(Et₂dtc)₂) and through the charge transfer from metal dithiocarbamate (M^II(Et₂dtc)₂, M = Zn or Cd) to C₆₀. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2072–2087, November, 2007.     

Magnetic properties of fullerene salts containing d- and f-metal cations (Co2+, Ni2+, Fe2+, Mn2+, Eu2+, Cd2+). Specific features of the interaction between C60·? and the metal cations

The interaction between the radical anions C₆₀ ^·− and divalent d- and f-metal (Co, Fe, Ni, Mn, Eu, Cd) cations in DMF and acetonitrile-benzonitrile (AN-BN) mixture was studied. Black solid polycrystalline salts (C₆₀ ^·−)₂{(M²⁺)(DMF) _x } (x = 2.4–4, 1–6) containing the radical anions C₆₀ ^·− and metal(ii) cations solvated by DMF were prepared for the first time and their optical and magnetic properties were studied. The salts containing Co²⁺, Fe²⁺, and Ni²⁺ are characterized by antiferromagnetic interactions between the radical anions C₆₀ ^·−, which result in unusually large broadening of the EPR signal of C₆₀ ^·− upon lowering the temperature (from 5.55–12.6 mT at room temperature to 35–40 mT at 6 K for Co²⁺ and Ni²⁺). The salts containing Mn²⁺ and Eu²⁺ form diamagnetic dimers (C₆₀ ⁻)₂, which causes a jumpwise decrease in the magnetic moment of the complexes and disappearance of the EPR signal of C₆₀ ^·− in the temperature range 210–130 K. A feature of salt 6 is magnetic isolation of the radical anions C₆₀ ^·− due to the presence of diamagnetic cation Cd²⁺. The salts prepared are unstable in air and decompose in o-dichlorobenzene or AN. Reactions of C₆₀ ^·− with metal(ii) cations in AN-BN mixture result in decomposition products of the salts that contain neutral fullerene dimers and metals solvated by BN. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1909–1919, September, 2008.     

Thermochemical properties of the Fe-analogue of cryolite, Na3FeF6

Relative enthalpies for low-and high-temperature modifications of Na₃FeF₆ and for the Na₃FeF₆ melt have been measured by drop calorimetry in the temperature range 723–1318 K. Enthalpy of modification transition at 920 K, δ_trans H(Na₃FeF₆, 920 K) = (19 ± 3) kJ mol⁻¹ and enthalpy of fusion at the temperature of fusion 1255 K, δ_fusH(Na₃FeF₆, 1255 K) = (89 ± 3) kJ mol⁻¹ have been determined from the experimental data. Following heat capacities were obtained for the crystalline phases and for the melt, respectively: C _p(Na₃FeF₆, cr, α) = (294 ± 14) J (mol K)⁻¹, for 723 = T/K ≤ 920, C _p(Na₃FeF₆, cr, β) = (300 ± 11) J (mol K)⁻¹ for 920 ≤ T/K = 1233 and C _p(Na₃FeF₆, melt) = (275 ± 22) J (mol K)⁻¹ for 1258 ≤ T/K ≤ 1318. The obtained enthalpies indicate that melting of Na3FeF6 proceeds through a continuous series of temperature dependent equilibrium states, likely associated with the production of a solid solution.      

Quenching of electronically excited Ln3+* ions by C60 fullerene

Quenching of electronically excited states of Ln^3+* ions generated upon photoexcitation of toluene solutions of Ln(acac)₃·H₂O (Ln = Tb, Eu) complexes by C₆₀ fullerene at 293 K was detected and investigated. The dependences of quenching efficiency on C₆₀ concentration obtained from data on the decrease in the photoluminescence intensity and Ln^3+* lifetimes obey the Stern-Volmer law. Quenching is due to inductive-resonant energy transfer from Ln^3+* to C₆₀ fullerene. The bimolecular rate constants for quenching, the overlap integrals of the Ln^3+* photoluminescence spectra with the C₆₀ absorption spectra, and the critical energy transfer distances were determined. No sensitized luminescence of C₆₀ in the system studied was detected. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 921–925, June, 2006.     

On the state of CH<Subscript>4</Subscript> molecule in the octahedral void of C<Subscript>60</Subscript> fullerite

Methane-intercalated fullerite (CH₄)_0.56C₆₀ was obtained by low-temperature precipitation from solution. Methane transition from the gas phase to the octahedral void of fullerite is accompanied by a bathochromic shift of normal vibrational frequencies (by 19 and 8 cm⁻¹ for ν₃ and ν₄, respectively). The methane ¹³C signal in the proton decoupling ¹³C NMR spectrum is observed as a singlet at δ−0.42. According to quantum chemical calculations using density functional theory, location of methane in the octahedral void of fullerite (C₆₀)₆ leads to a decrease in the total energy of fullerite by 4 kcal mol⁻¹.     

Rotation dynamics of C60 molecules in organic superconductor K3C60

The rotation dynamics of C₆₀ molecules in organic superconductor K₃C₆₀ has been investigated from the viewpoint of intramolecular interaction. It is determined that the rotation of C₆₀ at mom temperature has been frozen up within a small region of rotation angle (0°–50°), and pointed out that the reason for the freeze is the physical interaction rather than the geometrical hindrance. The computations of the interactions for alkali-doped compounds A_3-x A′ _x C₆₀ (x = 1, 2, 3; A, A′ = K, Rb, Cs) other than K₃C₆₀ have also been camed out. Fmm the obtained results, it is seen that the superconducting transition temperatures T, are strongly connected with the interactions in them, and this observation is consistent with the discovery of the correlation between T_c, and lattice constants a. Project supported by the National Natural Science Foundation of China.     

Facile preparation and electrochemical properties of large-scale Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> nanobelts

Large-scale Li_1+x V₃O₈ nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method. The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts is mainly determined by the calcination temperature. Electrochemical properties of the Li_1+x V₃O₈ nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li_1+x V₃O₈ nanobelts exhibit a high discharge capacity (278 mAh g⁻¹) and excellent cycling stability.