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.     

The reaction of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate with fullerene C60

Heating (100 °C, toluene) or photolysis (Nd³⁺ : YAG laser, = 532 mil, benzonitrile) of a mixture of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (Hantsch ester) (1) and fullerene C₆₀ under anaerobic conditions results in the formation of fullerene hydrogenation products and ethyl 2,6-dimethylpyridine-3,5-dicarboxylate, which is the product of dehydrogenation of1, identified by IR spectroscopy and mass spectrometry. The triplet state of C₆₀ is quenched by the Hantsch ester.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2531–2534, October, 1996.     

Interaction of the iridium(III) trihydridophosphine complex with fullerene C60 under thermal and photochemical excitation

The interaction of the PPh₃-stabilized iridium trihydrido complex H₃Ir(PPh₃)₃ with fullerene C₆₀ under thermal and photochemical excitation was studied under anaerobic conditions. Heating (100 °C) or photolysis by the visible light of the H₃Ir(PPh₃)₃-C₆₀ 650 nm, which are characteristic of the ·²-coordinated C₆₀ in several fullerene-containing metal complexes. The kinetic behavior of the H₃Ir(PPh₃)₃)-C₆₀ system in benzonitrile was investigated using a Nd³⁺-YAG laser (λ=532 nm). The quenching rate constant determined from the dependence of the effective first-order quenching constant of C₆₀(T) on the concentration of H₃Ir(PPh₃)₃ is equal to 1.1·10⁹ L mol⁻¹ s⁻¹. The quenching of C₆₀(T) by the iridium hydridophosphine complex follows the reductive mechanism to form a C₆₀ monoanion. The ESR signal with g=2.000 and ΔH=0.17 mT (at room temperature) and characteristic absorption bands in the near-IR region at 940, 1004, and 1076 nm support the formation of the C₆₀ monoanion during the interaction of the triplet-excited C₆₀ with H₃Ir(PPh₃)₃. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2145–2148, December, 1997.     

Quenching excited triplet C60 fullerene by tetracyanoethylene in benzonitrile

Quenching excited triplet³C₆₀ fullerene by tetracyanoethylene (TCNE) in a benzonitrile solution proceeds with a rate constant equal to (4.2±0.3) · 10¹⁸ (M · s)^–1. The formation of a radical ion pair [C₆₀ ⁺ · · · TCNE^–] was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1228–1230, July, 1993.     

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.     

Laser flash photolysis of fullerols of C60 and of C70 in aqueous solutions

Fullerols of C₆₀ and of C₇₀ [C₆₀(OH)_n, C₇₀(OH)_m], water-soluble fullerene derivatives, unlike some other fullerene derivatives (such as C₆₀ (C₄H₆O), C₆₀ (C₃H₇N) and C₆₀ [C(COOEt)₂]_x), do not result in excited triplet state but in ionization via monophotonic process in aqueous solutions with 248 nm laser. The quantum yields of formation of hydrated electron (Φ_e ⁻) are determined to be 0.08 and 0.11 for fullerols of C₆₀ and of C₇₀ respectively at room temperature (ca. 15°C) with KI solution used as reference. By laser flash photolysis and oxidation of sulfate radical anion SO₄ ⁻, the fullerol radical cation or neutral radical of C₆₀ is confirmed to be existent and the transient absorption spectra of fullerol radical cation of C₇₀ are observed for the first time. Project supported by the National Natural Science Foundation of China     

New complexes of fullerences C60 and C70 with CoII and MnII tetraphenylporphyrinates and their ESR study

Complexes of fullerenes C₆₀ and C₇₀ with cobalt(II) and manganese(II) tetraphenylporphyrinates of compositions Mn(TPP)·(C₆₀)₂(CS₂)_1.5 (1), Mn(TPP)·C₇₀(CS₂) _x , wherex<=1.25 (2), Co(TPP)·C₆₀(CS₂)_0.5 (3), and Co(TPP)·C₇₀(CS₂) _x , wherex<0.25 (4), were synthesized and studied by ESR spectroscopy. At 77 K, complexes1 and2 have singlet ESR spectra characteristic of the low-spin (S=1/2) state of Mn^II, withg=2.002 and linewidths of 250 G and 300 G, respectively, and differing significantly from that of the initial Mn^II(TPP) (g ₁=5.9 andg=2.0,S=5/2). The spectra of complexes1 and2 exposed to oxygen exhibit hyperfine structure due to interaction with⁵⁵Mn and¹⁴N nuclei. The ESR spectra of complexes3 and4 are asymmetric (<g>=2.4, ΔH _pp=(500–600) G), which is due to the overlap of parallel and perpendicular spectral components. The absence of ESR signals from C₆₀ ^.− and C₇₀ ^.− radical anions makes it possible to conclude that the formation of complexes1–4 is not accompanied by electron transfer from Co(TPP) and Mn(TPP) to fullerences C₆₀ and C₇₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 722–725, April, 1999.     

[60]Fullerene diol issued from pentaerythritol derivatives

A new [60]fullerene diol is synthesized in good yield, in two steps starting from reaction of C₆₀²⁻ anion with the benzylideneacetal derived from 2,2-bis(iodomethyl)-1,3-propanediol. The corresponding [60]fullerene bis-mesylate is also formed in a similar way starting from bis-iodo bis-mesylate compound in the same series. The scope of this fullerene diol in synthesis is exemplified by its easy esterification with 4-formyl benzoyl chloride.     

Hydrosilylation of fullerence C60

The hydrosilylation of C₆₀ by diphenylsilane was studied. Silicon-containing derivatives C₆₀H _n (HSiPh₂) _n (n=2, 4, 6) were obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1697–1699, September, 1997.     

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.     

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.     

Spectra of optical phonons and low-energy electronic transitions in C60/TMPD and C60/TPA single crystals

Single Crystals of C₆₀/TMPD and C₆₀/TPA have been grown from a chlorobenzene solution. Optical transmission spectra of single crystals of fullerene complexes withN,N,N,N-tetramethyl-p-phenylenediamine (TMPD) and triphenylamine (TPA) are studied in the spectral range from 600 to 16000 cm^–1. Splitting of the intramolecular vibration of C₆₀ is observed at 1428 cm^–1, which is likely caused by freezing of the rotation of the C₆₀ molecules due to their interaction with amines. Single crystals of C₆₀/TMPD differ from those of C₆₀/TPA by a decrease in the vibration frequency at 1428 cm^–1, vibrations of the C-C bonds of the TMPD molecule, and the redistribution of the forces of the oscillators of the vibrations of the C-N bonds. These peculiarities are interpreted to be the result of partial electron transfer from TMPD to C₆₀ in the C₆₀/TMPD single crystals. The electron transfer in the C₆₀/TPA system is less pronounced.Translated fromIzvestiya akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1459–1464, June, 1996     

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.     

Voltammetric studies of microcrystalline C60 adhered to a carbon electrode surface and placed in contact with aqueous electrolyte containing potassium ions

The reduction of microcrystalline C₆₀ fullerene, adhered at a carbon electrode and immersed in aqueous electrolyte, has been studied under various voltammetric conditions. This work reports mainly the voltammetric studies carried out principally in electrolyte containing potassium ions. Comparison of adherence techniques, such as solvent casting and mechanical transfer methods, are made to assess if the type of adhered techniques has any significant influence on the observed electrochemistry. The solvent casting method is found to produce three peaks in the potential for C₆₀^0/n- redox couple as compared to a single and large peak produced when a mechanical transfer technique is employed. When the reduction potential of microcrystalline C₆₀ in the presence of K⁺ is compared with other cations, such as Li, Na, Rb and Cs, it is observed that the shift of reduction potential follows the change in the hydration energy in the order Cs>Rb>K>Na>Li. In a mixed electrolyte study of CsCl/KCl, the reduction potential and peak shape of C₆₀^0/n- redox couple during cyclic voltammetry is observed to change with concentration of the cations and the observed electrochemistry can be attributed to a cation-exchange mechanism. The reduction of C₆₀ is irreversible in aqueous electrolyte containing alkaline cations as the re-oxidation process does not produce any observed electro-activity. Evidence of the formation of a passive coating of K _n C₆₀ fulleride, which does not appear to undergo dissolution is obtained under cyclic voltametric conditions. This coating remains electrochemically active in the presence of tetrabutylammonium ions in acetonitrile. Scan rate, chronocoulometric, and scanning electron microscopic studies provide evidence of the presence of a surface process involving solid–solid transformation.     

Water-soluble polyketones and esters as the main stable products of ozonolysis of fullerene C60 solutions

Stable ozonolysis products of C₆₀ solutions in CCl₄, toluene, and hexane were studied by elemental analysis, HPLC, and UV and IR spectroscopy. Polyketones and esters were established for the first time to be the main stable products, whose content increased during the whole ozonolysis time (1 h). Epoxides C₆₀O _n (n = 1—6) are accumulated within 1—3 min, and after 5 min of ozonolysis their concentration decreases to zero. Fullerene C₆₀ disappears from the reaction solution due to its conversion to oxides and mechanical capturing of C₆₀ by these oxides to form a precipitate. The oxidation of C₆₀ is completed in the solid phase by the formation of the C₆₀O₁₆ oxide in which 9.68 O atoms fall on fullerene polyketones, 6 O atoms are attributed to esters, and 0.32 O atoms fall per epoxides. The optimum medium for preparation of the C₆₀ oxides is CCl₄ rather than traditional toluene, which reacts with ozone in the side reaction to form products containing active oxygen. The C₆₀ cage is raptured during ozonolysis because of the C=C bond cleavage to form two C=O groups at the ends of the open hexagon. Ozonolysis of C₆₀ solutions in CCl₄ is efficient for synthesis of water-soluble fullerene oxides due to the high yield and solubility of polyketones and esters in water.     

Annealing Temperature Dependence of the Size of C60 Clusters in C60-Doped Silicon Oxide Films

C₆₀-doped silicon oxide thin films were prepared by spin-coating a viscous solution formed upon soaking at 40°C an acidic toluene/ethanol solution of C₆₀, phenyltriethoxysilane, and tetraethoxysilane with a C₆₀–to–Si molar ratio of 2.5 × 10^–3. The films were submitted to annealing at 300–500°C in Ar to investigate variation in the size of C₆₀ clusters embedded in the films by photoluminescence spectroscopy. The film before annealing was found to contain the clusters consisting of ca. 60 C₆₀ molecules, suggesting that C₆₀ is present well-dispersed in the film. The molecules in the film aggregated to increase the size with increasing annealing temperature, indicating that the molecules diffuse easily in the film upon heating and therefore the size of the clusters is controllable with the annealing temperature.     

Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

Copolymerization of Fullerene (C60) and Methyl Methacrylate (MMA) using Triphenylbismuthonium Ylide as a Novel Initiator and Characterization of the Copolymers (C60-MMA)

Copolymerization of fullerene (C₆₀) with methyl methacrylate (MMA) was carried out using triphenylbismuthonium ylide (abbreviated as Ylide) as a novel initiator in dioxan at 60°C for 4 h in a dilatometer under a nitrogen atmosphere. The reaction follows ideal kinetics: R_p∝ [Ylide]^0.5[C₆₀]^?1.0[MMA]^1.0. The rate of polymerization increases with an increase in concentration of initiator and MMA. However, it decreases with increasing concentration of fullerene due to the radical scavenging effect of fullerene. The overall activation energy of copolymerization was estimated to be 57 KJ mol^?1. The fullerene-MMA copolymers (C₆₀-MMA) were characterized by FTIR, UV–Vis, NMR and GPC analyses.     

Reduction of C60 and C70 by primary amines: Optical and ESR studies

Radical anions C70- and C70 2- were obtained in vacuo by the reaction of I-amino3-propanol (AP) and 1,5-diaminopentane (DAP) with fullerene C70. The radical anions were identified by visible/near IR (X = I372 and I172 nm, respectively) and ESR spectroscopies. The temperature dependences of the ESR spectra were studied for the C₆₀-AP, C₇₀-AP, and C70-DAP systems. At low temperatures (I5-45 K), the ESR spectrum for C60 is close to that for species with axial symmetry of theg-factor (q_| = 2.000 and g, = I.995). The anisotropy of theg-factor is averaged, when the temperature increases. At T > I48 K the averaged line is broadened, and the sharp signal with g = 2.0001 overlaps this broad line. The intensity of the narrow line increases, when the temperature increases. The ESR spectrum observed in the C₇₀-AP system at I2.5 K may be tentatively described as a superposition of two ESR spectra, namely, the ESR spectra of a radical with g_| = 2.0042 and g, = 2.0015 (presumably a radical cation) and of C₇₀ ^– with q_| = 2.000 and g = I.994. The spectra of the sample in which C70 is present mainly as C₇₀ ^2– exhibit only a line with g = 2.0004.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. I, pp. 103–108, January, 1996.     

Electrochemical behavior of fullerene C60 and substituted fullerenes immobilized on an electrode surface

The effect of substituents with different donor capabilities, which are inserted into a molecule of fullerene C₆₀, on the kinetics and thermodynamics of redox conversions of fullerenes that are immobilized on an electrode, is studied for the first time. To this end, redox conversions that occur with rubbed-on films of fullerene and fulleropyrrolidines are studied using cyclic voltammetry in 0.5 M KCl/H₂O and a 0.1 M (C₄H₉)₄NBF₄/AN solution in acetonitrile. A hypothesis that the kinetics of redox conversions occurring with films of individual fullerenes is defined largely by changes in the structure of initial films in the process of their cathodic doping is used. The effect of the substituents is explained in the framework of this hypothesis by a transition from a dense crystalline structure of nonsubstituted fullerene C₆₀ to an amorphous structure of substituted fullerenes. It is demonstrated that the formal potentials corresponding to redox conversions of fullerenes in a solid cationic lipid matrix are defined by the energy of interaction of anions, which are products of reduction of fullerenes, with cations of the matrix. As a result of this interaction, the formal potentials of the process of cathodic doping shift to less negative values. It is established that the insertion of a donor substituent and increase in its donor capability amplify the energy of interaction of the fullerene anions with the lipid cations.