Crystal structures of chloroform solvates of fullerenes

The chloroform solvates of C₆₀ and C₇₀ fullerenes and of the C₆₀/C₇₀ mixture were synthesized and investigated by X-ray powder diffraction.     

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.     

Photosynthetic reactions in fullerene based donor-acceptor complexes

Donor-acceptor interaction changes essentially the terms of the ground state of binary complexes imparting them a multi-well, in particular, two-well form. A quantum chemical analysis of formation conditions for the amine derivatives of fullerenes depending on the type of the term has been performed by the example of binary complexes, including fullerenes C₆₀ and C₇₀ as acceptors of electrons and amines as donors,. It is found that the addition reaction of amines to fullerene hampered between neutral molecules can occur when the latter are ionized by light.     

Determinations of combustion and formation enthalpies of C60 and C70

By using a micro-bomb calorimeter, the standard enthalpies of combustion of C₆₀ and C₇₀ have been determined to be - (25 947.1±8.5) and - (29 956.1 ± 8.9) kJ/mol respectively. A g. 1. c. analysis indicated that the amounts of residual organic solvents in the samples were very small, and their effects on the final results were negligible. The energy of combustion ofC60 determined in this work is in agreement in the uncertainty interval with that determined by means of traditional calorimeter using macro amount of sample. The enthalpies of formation of these two substances have been derived. The strain energies in the molecules of C₆₀ and C₇₀ were estimated by a bond energy scheme and by using corannulene as the model compound, the results estimated from different methods are very close. Project supported by the National Natural Science Foundation of China (Grant No. 29473143)     

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.     

Charge transfer in complexes of C60 and C70 in solutions and solid state

Electronic absorption spectra of complexes of C₆₀ and C₇₀ fullerenes with donors, tetrathiafulvalene and pyranylidene derivatives, were studied in solutions and in the solid state. Charge transfer bands were found in the 680–1300 nm range. The charge transfer energies (hv _ct) for the C₆₀ and C₇₀ complexes in solutions are close and almost independent of the solvent polarity. For the C₆₀ complexes in the solid state, the dependence ofhv _ct on the ionization potential (IP) of donors was found to behv _ct=0.82IP–3.93 eV. In the C₆₀ complexes in the solid state, thehv _ct values are 0.15–0.20 eV lower than those in the solution. The linear dependences ofhv _ct onIP of donors for the C₆₀ complexes lie 0.6–0.7 eV higher than those in the complexes with tetracyanoethylene (TCNE). This is associated with lower values of the electron affinity of C₆₀ and the energy of the electrostatic interaction in the fullerene complexes as compared to those of the TCNE complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 478–483, March, 1999.     

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.     

Self-assembly of uncharged amphiphilic porphyrins and incorporation of C60 fullerenes in water

We synthesised an uncharged amphiphilic porphyrin, meso-tetrakis-(3,5-di-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-phenyl)-porphyrin, and investigated the supramolecular self-assembly of the porphyrins and the incorporation of C₆₀ molecules into the assembly in aqueous solutions. Spectroscopic and dynamic light scattering studies on the assembly of the amphiphilic porphyrin support that the amphiphilic porphyrins are likely held together through enhanced π–π interactions by pronounced hydrophobic effects in aqueous solutions. It was also found that C₆₀ molecules are efficiently incorporated into the assembly. The fluorescence emitted from the porphyrin ring of the porphyrin/C₆₀ co-assembly in aqueous solution is largely quenched, implying the presence of strong electronic interactions between C₆₀ and porphyrin molecules in the supramolecular assembly.     

Reactions of carbanions of bis(dialkoxyphosphoryl)bromomethane with fullerenes C60 and C70

The reactions of carbanions of bis(dialkoxyphosphoryl)bromomethanes with fullerenes C₆₀ and C₇₀ afforded new bis(dialkoxyphosphoryl)methanofullerenes C₆₀ and C₇₀, respectively, whose structures were established by spectroscopic methods.     

Characterisation and determination of fullerenes: A critical review

A prominent sector of nanotechnology is occupied by a class of carbon-based nanoparticles known as fullerenes. Fullerene particle size and shape impact in how easily these particles are transported into and throughout the environment and living tissues. Currently, there is a lack of adequate methodology for their size and shape characterisation, identification and quantitative detection in environmental and biological samples. The most commonly used methods for their size measurements (aggregation, size distribution, shape, etc.), the effect of sampling and sample treatment on these characteristics and the analytical methods proposed for their determination in complex matrices are discussed in this review. For the characterisation and analysis of fullerenes in real samples, different analytical techniques including microscopy, spectroscopy, flow field-flow fractionation, electrophoresis, light scattering, liquid chromatography and mass spectrometry have been reported. The existing limitations and knowledge gaps in the use of these techniques are discussed and the necessity to hyphenate complementary ones for the accurate characterisation, identification and quantitation of these nanoparticles is highlighted.     

“Chemical portrait” of fullerene molecules

Chemical activity of fullerene molecules is associated with a partially radical character of these molecules caused by the presence of effectively unpaired electrons (EUE). Values of the total number of N _D and partial distribution N _DA of EUE over the atoms in a singlet state of molecules C₆₀ and C₇₀ have been calculated. “Chemical portraits” of molecules are presented, and N _DA values are proposed to be used as indicators for chemical activity of atoms and to predict thereby the position of favorable atom-atom contacts in addition reactions with participation of these molecules. Bases of “computational synthesis” procedures for fullerene C₆₀ derivatives are exemplified by initial phases of its fluorination.     

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.     

Enantioanalysis of R-deprenyl based on its molecular interaction with C70 fullerenes

Two enantioselective, potentiometric membrane electrodes based on [5,6]fullerene-C₇₀ (1) and diethyl (1,2-methanofullerene C₇₀)-71-71-dicarboxylate (2) immobilized in carbon paste, were designed for the enantioanalysis of R-deprenyl. The electrodes exhibited near-Nernstian slopes: 57.90 (1) and 59.00 mV/decade of concentration (2), respectively with low limits of detection 5.9 × 10⁻¹¹ (1) and 9.6 × 10⁻¹¹ mol/L (2), respectively. The linear concentration ranges are between 10⁻¹⁰ and 10⁻⁴ mol/L (1) and between 10⁻⁹ and 10⁻⁴ mol/L (2), respectively. The different characteristics involved in the molecular interaction between R-deprenyl and C₇₀ fullerenes were explained, namely (i) the stability of each molecule and (ii) the explanation of the molecular mechanism of interaction, using restricted Hartree-Fock theory, 3-21G(*) RHF-basis set. Furthermore, two intermolecular forces of interactions confer the stability of the electrodes; electrostatic interaction and moderate hydrogen bond interaction. Stability and feasibility of all the generated structures involved in this analysis were supported by their respective fundamental frequencies and energy minima.R-deprenyl can be recovered with average recoveries higher than 99.10% (RSD < 0.03%) from synthetic mixtures between R- and S-deprenyl. The high selectivity and enantioselectivity made possible the enantioanalysis of R-deprenyl in its pharmaceutical formulations.     

Inclusion properties of 3-fluoromesotetraphenylporphyrin with C60 and C70

To improve the selectivity ratio of C70 over C60, a new designer molecule, viz., 3-fluoromesotetraphenylporphyrin (1) has been reported in the present investigations. Fluorescence studies reveal that the Q-absorption band of 1 gets sufficient quenching effect upon addition of both C60 and C70. Binding constants (K) of the C60/1 and C70/1 complexes are estimated to be 580 and 10,800 dm3 mol(-1), respectively. Thus, K(C70)/K(C60) is approximately 19 which is very large and even comparable with other macrocyclic host molecules like calix[5]arene, azacalix[m]arene[n]pyridine, cyclotriveratrylenophane and calixarene bisporphyrin. 1H NMR chemical shift measurements show that the -NH- proton of 1 suffers more shifts in presence of C70 compared to C60. This finding also offers a good support in favor of high K value for C70/1 complex as well as large selectivity ratio of C70 over C60.     

Molecular mechanics on bonding and non-bonding interactions in (atom@C60)

The interactions between the embedded atom X (X = Li, Na, K, Rb, Cs; F, Cl, Br, I) andC60 cage in the endohedral-form complexes (X@C₆₀) are calculated and discussed according to molecular mechanics from the point of view of the bonding and non-bonding. It is found from the computational results that for atoms with radii larger than Li’s, their locations with the minimum interaction in (X@C₆₀) are at the cage center, while atom Li has an off-center location with the minimum interaction deviation of ~0.05 nm, and the cage-environment in C₆₀ can be regarded as syhero-symmetry in the region with radiusr of ~0.2 nm. It is shown that the interaction between X and C₆₀ cage is of non-bonding characteristic, and this non-bonding interaction is not purely electrostatic. The repulsion and dispersion in non-bonding interactions should not be neglected, which make important contribution to the location with minimum interaction of X, at center or off center. Some rules about the variations of interactions with atomic radii have been obtained. Project supportt:d by the National Natural Science Foundation of China.     

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     

Ionic fullerene compounds containing negatively charged dimers and coordinatively bound anions

The review summarizes the results of investigations of ionic fullerene compounds containing negatively charged dimers and fullerene anions coordinated to metalloporphyrins. Fullerene radical anions were found to form diamagnetic singly bonded (C₆₀ ⁻)₂ and (C₇₀ ⁻)₂ dimers. Dimerization is reversible and leads to paramagnetic—diamagnetic phase transitions or a decrease in the magnetic moment of the complexes. The temperature, at which dissociation of the (C₆₀ ⁻)₂ dimers begins, varies from 140 to 320 K; the corresponding temperature for the (C₇₀ ⁻)₂ dimers varies from 260 to 360 K and higher. We prepared the first doubly bonded (C₆₀ ⁻)₂ dimer. At 300 K, this dimer exists as a biradical. The fullerene radical anions form Co—C coordination bonds with cobalt(II) porphyrinates. The resulting anions are diamagnetic. In some cases, Co—C coordination bonds undergo reversible dissociation, resulting in magnetic transitions from the diamagnetic to the paramagnetic state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 361–381, March, 2007.     

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.     

Thermodynamic properties of some polymeric forms of fullerite C<Subscript>60</Subscript> at temperatures ranging from 0 to 320 K

The temperature dependences of the heat capacityC ⁰ _p of fullerites C₆₀ were studied at temperatures ranging from 5 to 320 K in an adiabatic vacuum calorimeter with an accuracy of 0.4–0.2%. The fullerite C₆₀ samples were prepared by treating the starting fullerite C₆₀ under 8 GPa at 920 and 1270 K and “quenched” by a sharp decrease in pressure to −10⁵ Pa and in temperature to ∼300 K. Fullerite C₆₀(8 GPa, 920 K), a crystalline polymer with layered structure formed by polymerized fullerene C₆₀ molecules, was obtained at 920 K and 8 GPa. Fullerite C₆₀(8 GPa, 1270 K), a three-dimensional polymer with a graphite-like structure formed by fragments of decomposed C₆₀ molecules and containing many C(sp³)−C(sp³) bonds, was obtained at 1270 K and 8 GPa. Both polymers are metastable polymeric phases. The anomalous character of the temperature dependence of the heat capacity was revealed in the 49–66 K range for the polymer formed at 1270 K. The thermodynamic functions of the substances under study were calculated for the 0–320 K region along with entropies of their formation from graphite. The entropies of transformation of the starting fullerite C₆₀ into metastable phases and that of intertransformation of phases were estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 277–281, February, 2000.