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We have measured the electrical resistivity as a function of temperature up to pressures of 25 GPa of pure fullerenes C60, C70 and the compound C60I4. For the three materials the best fit in our temperature range corresponds to a three-dimensional variable-range hopping conductivity, signature of an important disorder. A dramatic decrease of the resistivity, by two orders of magnitude per GPa, is observed at low pressures. However, no metallic state is attained as all the samples present a phase transformation in the high-pressure range, probably originated by the crossover from sp2 to sp3 hybridization of the carbon orbitals at high pressures.

Optically pure bicyclo[3.3.0]octane-2,6-dione is easily obtained with a yield of 4% for each enantiomer from 1,5-cyclooctadiene in 5 steps, by resolution of the intermediate diol with menthyloxyacetic acid. Its CD is 60% larger than twice the CD of a corresponding monoketone indicating interactions between non-conjugated chromophores.

Alkynes R-CCH were obtained in good yield through a one-pot procedure by a sequence of reactions starting from a Wittig-type condensation of the aldehydes RCHO with the ylide derived from dibromomethyltriphenylphosphonium bromide 5. The same reactions could also be used to prepare the intermediate dibromoalkenes RCHCBr2, and in certain cases, the bromoalkynes R-CCBr.

Iodoalkynes RCCI were obtained in good yield through a one-pot procedure by reaction of the aldehydes RCHO with diiodomethyltriphenylphosphorane first generated in situ from iodoform, triphenylphosphine and t -BuOK.

The design of the smallest spheroarenes (C(N) molecules based on trivalent polyhedral framework, a class which subsumes fullerenes) of any point-group symmetry is presented. The role of Curie's principle is discussed. Some molecules whose carbon backbone is a nonplanar graph are described.

A simplified procedure is described for assigning Cahn-Ingold-Prelog descriptors to stereocentres in spheroalkanes (the CnHn molecules, with n even, based on trivalent, polyhedral carbon frameworks, a class which subsumes the fulleranes). By extension, similar descriptors can be found for the atoms of fullerenes and related carbon-only molecules. Assignment maps are given for chiral fullerenes C28 C76, C78, C84 and C140, and for a number of spheroalkanes. Cases of breakdown of the simple procedure for triangle-rich spheroalkane molecular graphs are discussed.

Two charged aminoxyls, ammonium (1-oxyl-2,5,5-trimethylpyrrolidin-2-yl)methanesulfonate and ammonium 2-methyl-2-[(N-(4-tert-butylphenyl)oxyl]propanesulfonate, obtained by methods easily adaptable to the preparation of various other aminoxyls are totally soluble in water but are partially associated in other solvents.

A novel 2∶1 (permethylated-β-cyclodextrin)–fullerene conjugate has been synthesised; highly soluble in cold water with formation of aggregates, it displays a negative solubility coefficient and has a partition coefficient between octanol and water (Log P = 1.58) in the suitable range for biological studies.

Ten-sided prismatic crystals of C 60 grown by evaporation of n-hexane solutions have been characterized by scanning electron microscopy and X-ray diffraction. Various unusual morphologies have been observed. X-ray precession photographs confirm the decagonal symmetry and they are analyzed by means of twinning of monoclinic variants related by π/5 rotations. Possible twinning mechanisms are discussed.

The influence of two types of impurities, toluence and C 70 on high resolution 13 C NMR parameters of solid C 60 is reported. The evolution of the spectrum upon thermal treatment of the sample is described and the solvent free material is characterized. A strong dependence of the measured spin-lattice relaxation time T 1 on the thermal history of the sample and on the C 70 presence is analysed.

High resolution heat capacity measurements of the prototypic fullerene, C60, are presented between 13 and 300 K. The well-documented first-order phase transition is clearly observed at 257.6 K and is associated with enthalpy and entropy changes of 7.54 and 30.0 J K−1 mol−1, respectively. A more subtle transition is observed at 86.8 K. This transition is attributable to the onset of orientational glass behaviour related to the kinetics of molecular reorientation. The rate of the enthalpy relaxation at the glass transition is accurately reproduced by a simple exponential function. The Arrhenius parameters describing the temperature dependence of the relaxation time are Ea = 22.2 ± 1.0 kJ mol−1 and τ0 = 4×10−11±1s. At low temperatures, solid C60 is a glassy crystal in which molecular orientational disorder is frozen in as a consequence of the long relaxation time of the molecular reorientation.

A single crystal of C60 grown from a toluene solution has been studied by X-ray diffraction at room temperature. The lattice is face-centered cubic, with space group Fm3m and Z = 4, which agrees with previous powder diffraction measurements. It is shown that, contrary to what is obtained in other plastic crystals, the Pauling-Fowler model (the so-called free rotation one), which implies an isotropic molecular disorder, gives a better description of the molecular packing than the site model does. It is concluded that the molecules undergo a rotational diffusion as previous molecular dynamics simulations have described.

X-ray diffraction has employed to study the low temperature structural behavior of C60 crystals. The intensity (I) of selected reflections which appear at the face-centered cubic-simple cubic transition was measured as a function of temperature down to 23 K. This orientational ordering transition is found at T0=259±1 K. It displays a hysteresis of about 1 K but no discontinuity of the intensity at T0. Anomalies in d(I)/d(T) around 155 K and 85 K are clearly revealed. They are associated with changes in the C60 molecular reorientations and their origin is discussed.

C 60 fullerene may crystallize from benzene solutions as thin yellow plates, whose morphology has suggested the existence of a hcp modification. By means of single crystal X-ray diffraction, we show that these plates crystallize in the cubic system. Surprisingly, these plates do not exhibit the phase transition near 260K. Nevertheless, the existence of a hcp variety cannot be discarded since scanning electron microscopy reveals the presence of hexagonal prims in a sample made of pure C 60 powder

X-ray measurements reveal a tenfold symmetry in a single crystal of fullerene C60 grown from a n-hexane solution. Among various hypotheses, that of a quasicrystal is considered.

The new oxaziridine nitroxide, 2,2,4,4,6-pentamethyl-7-oxa-1,3-diaza-bicyclo[4.1.0]heptan-3-oxyl, has been obtained in 90% yield by oxidation of 2,2,4,6,6-pentamethyl-1,2,5,6-tetrahydro-pyrimidine with MCPBA in ether. This nitroxide is stable in the solid state or in non-protic solvents. It was converted to the known 2,2,4,6,6-pentamethyl-1,2,5,6-tetrahydro-pyrimidine-1-oxyl by successive reduction with LiAlH4 and oxidation with Ag2O, with a reproducible yield of 16% from the starting tetrahydropyrimidine.

Iodoalkynes RCCI were obtained in good yield through a one-pot procedure by reaction of the aldehydes RCHO with diiodomethyltriphenylphosphorane first generated in situ from iodoform, triphenylphosphine and t -BuOK.

Two β-cyclodextrin–C60 conjugates ( 3 and 4 ) with a flexible linker at the secondary face of cyclodextrin are synthesized by a single reaction of 2-(ω-azidoundecanyl)-2-O-heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin ( 2 ) and C60, both of which display satisfactory water solubility. Structural analyses show that 3 is a closed [5,6] aziridinofullerene, whereas 4 is a bis-adduct derivative. Using rhodamine B (RhB) as a guest molecule, the inclusion complexation behavior of 3 was investigated in aqueous solution.

The chemistry of 2,2,4,4-substituted pentane derivatives has been investigated with the aim of providing a flexible and versatile synthetic route to pyrimidinyl nitronyl nitroxides, in which the bis-N-oxy fragment is incorporated in a six-membered ring. The synthesis of 2,4-diamino-2,4-dimethylpentane and 2,4-bis(hydroxylamino)-2,4-dimethylpentane, convenient precursors of these nitroxides, is described and full characterization of a series of pyrimidinyl nitronyl nitroxides is reported, along with a preliminary study of their coordination properties.

A degree of chirality is a function that purports to measure the amount of chirality of an object: it is equal for enantiomers, vanishes only for achiral or degenerate objects and is similarity invariant, dimensionless and normalisable to the interval [0,1]. For a tetrahedrons of non-zero three-dimensional voluine, achirality is synonymous with the presence of a mirror plane containing one edge and bisecting its opposite, and hence it is easy to design degree-of-chirality functions based on edge length that incorporate all constraints. It is shown that such functions can have largest maxima at widely different points in the tetrahedral shape space, and by incorporation of appropriate factors, the maxima can be pushed to any point in the space. Thus the phrase "most chiral tetrahedron" has no general meaning: any chiral tetrahedron is the most chiral for some legitimate choice of degree of chirality.

The classical chemical structure theory (CST) provides “localised” qualitative models for the structure and reactivity of organic molecules, while, in addition to quantitative methods, the modern molecular orbitals (MO) theory provides “delocalised” qualitative models. In particular, these two theories provide two different descriptions of the ethylenic double bond, bent bonds and σ/π orbitals, respectively. In the framework of CST, a graphical model of aromaticity and antiaromaticity, related to a classical model of Woodward–Hoffmann rules, is presented. By application of Linnett's double-quartet theory, a new representation for benzene is proposed. It can be easily visualised when a new split representation of Linnett-type formulae is used.

Pyrimidinyl nitronyl nitroxides where the bis-N-oxy fragment is included in a six-membered ring were prepared from diacetonamine by a sequence of reactions including a Grignard reaction, a Ritter reaction and oxidation of the intermediate pyrimidine; the properties of the 2-phenyl-substituted representative are fully described.

Starting from the topological arrangement of carbon atoms an algorithm is given for the construction of nanotube Cartesian coordinates. The final relaxed structures were obtained by a molecular mechanics calculation where the carbon‐carbon interactions were supposed only between neighboring atoms of the initial tiling. In a given tiling we obtained toroidal or helical structures depending on the special position of the super cell parallelogram.

Usually the symmetry of a given molecule is described with the help of a point group. Here we present a method where the symmetry is characterized by a function from the range [0,1] to the set of point groups. Using this function we measured the molecular symmetries and chiralities for the fullerenes C20 : 1, C24 : 1, C26 : 1, C28 : 1 and C28 : 2.

Measurements on the temperature dependence of the specific heat of pure C60 in the range 4 < T < 300 K are reported. A large hysteresis is observed between 165 and 270 K. On cooling, two peaks are observed, respectively, around 255 and 165 K. On heating, only one large peak is observed at 255 K. These results are tentatively discussed in terms of the dynamics of the C60 molecules in the crystal.

IN one of the pioneering studies of magnetism at the microscopic level, Heisenberg1 concluded that ferromagnetism could not exist in compounds consisting only of light elements. A few well defined2, purely organic materials (consisting only of the elements carbon, hydrogen, oxygen and nitrogen) have subsequently been found3–5 to exhibit evidence of ferromagnetic interactions at low tem-peratures, with a small number of these showing a transition to a true ferromagnetic state. For example, the p-nitrophenyl nitronyl nitroxide radical has a Curie (transition) temperature of 0.60 K (ref. 6), and a possible ferromagnetic transition has been identified7,8 in a C60-based ionic complex. More recently, it was reported9 that the magnetization and magnetic susceptibility behaviour of a crystalline nitroxide biradical, N,N′-dioxy-l,3,5,7-tetramethyl-2,6-diazaadamantane, are indicative of ferromagnetic interactions. Here we report the existence of a ferromagnetic transition in this system, with a Curie temperature of 1.48 ± 0.02 K. As yet, this is the highest transition temperature found for a purely organic, non-ionic material.

It is shown that for an electronic cluster with three magnetic moments of spin 12 at the corners of an arbitrary triangle, coupled by dominant isotropic exchange interactions, it is impossible to obtain the three exchange parameters from susceptibility data only. EPR is of no help if the interacting moments have the same isotropic g value. On the other side it is outlined that when some of the Lande factors are different, combination of susceptibility and EPR data, including intensities of the allowed transitions, leads to the determination of all the unknown parameters. A specific example of a cluster involving two nitroxide radicals coupled with a Cu2+ ion is investigated.

The new oxaziridine nitroxide, 2,2,4,4,6-pentamethyl-7-oxa-1,3-diaza-bicyclo[4.1.0]heptan-3-oxyl, has been obtained in 90% yield by oxidation of 2,2,4,6,6-pentamethyl-1,2,5,6-tetrahydro-pyrimidine with MCPBA in ether. This nitroxide is stable in the solid state or in non-protic solvents. It was converted to the known 2,2,4,6,6-pentamethyl-1,2,5,6-tetrahydro-pyrimidine-1-oxyl by successive reduction with LiAlH4 and oxidation with Ag2O, with a reproducible yield of 16% from the starting tetrahydropyrimidine.

A physically realistic set of Cartesian coordinates is obtained for toroidal systems of trivalent atomic structures, using the eigenvectors of the topological matrix. In contrast to previous suggestions we present here a four-vector procedure.

THE bonding between molecules in bulk solid C60 is extremely weak, making it a narrow-band semiconductor with an energy gap of 1.5 eV (ref. 1) for the face-centred cubic phase. Doping with alkali metals produces a metallic state which can be superconducting at temperatures as high as 33 K (ref. 2). The intermolecular coupling should have an important influence on the conductivity of the pure, semiconducting state: stronger coupling might induce a transition to a metallic or possibly even superconducting state, as is the case for silicon3, or it may result in a covalent solid such as diamond4. We have explored these possibilities by measuring the electrical resistivity of solid granular C60 up to pressures of 25 GPa. Our results show that the magnitude of the gap and the resistivity decrease with increasing pressures as the sample volume5 decreases. But eventual gap closure to give a metallic state is not observed; instead, there is a sudden transition at 15–20 GPa to a more insulating phase, possibly with covalent intermolecular bonding.

International audience; The stereochemical relationships between the isomeric 5,6-dimethyl-5,6-dinitrodecane-2,9-diones and theirreduction products (the title compounds) have been established

The three [6,6]-ring bridged methanofullerenes 1, 2, and 3 were synthesized; their ground-state absorption spectra in toluene and cyclohexane solutions are presented and possible assignments discussed. Although these three molecules are very different, they have very similar triplet–triplet spectra and near-unity values for the quantum yield for O2(1Δg) production by energy transfer from the triplet states, implying that the quantum yield of triplet production is approximately 1.

A high-performance liquid chromatographic (HPLC) assay method for C60 fullerene, in blood, liver and spleen using photodiode-array detection or mass spectrometric detection (LC-MS) and C70 fullerene, as the internal standard, is described. The recovery from mouse blood and tissues spiked with micronized C60 exceeds 90%. The method is linear from 0.05 to 200 mg of C60 per liter of blood and from 0.05 to 5.00% of C60 per tissue weight. The limit of detection of the method is 0.1 ng of C60 per injection. This method was applied to mouse blood and tissue samples after intraperitoneal administration of a micronized C60 suspension.

Alkylation of C 60 in tetrahydrofuran with tert -butyl chloride and lithium gives a variety of products. Adducts of general formula C 60 H n ( t -Bu) q O x (thf) y (where t -Bu is the tert -butyl group and thf the tetrahydrofuryl group (C 4 H 7 O)) have been detected by mass spectrometry, with n ≤ 8, q + y ≤ 18 and x = 0, 1, 2 depending on experimental conditions. IR and NMR spectra of products confirm these assignments.

A novel 2:1 (permethylated-beta-cyclodextrin)-fullerene conjugate has been synthesised; highly soluble in cold water with formation of aggregates, it displays a negative solubility coefficient and has a partition coefficient between octanol and water (Log P = 1.58) in the suitable range for biological studies.

The hetero-Cope rearrangement of 4-tert-butyl-phenyl-tert-butylhydroxylamine provides an easy access to the corresponding ortho-bromoaniline, converted to the new highly water-soluble nitroxide, potassium 5-tert-butyl-2-(tert-butyl-aminoxy)-benzoate. The parent carboxylic acid was found to be very persistent in water at pH 1.

Two charged aminoxyls, ammonium (1-oxyl-2,5,5-trimethylpyrrolidin-2-yl)methanesulfonate and ammonium 2-methyl-2-[(N-(4-tert-butylphenyl)oxyl]propanesulfonate, obtained by methods easily adaptable to the preparation of various other aminoxyls are totally soluble in water but are partially associated in other solvents.

Low-temperature specific heat and differential-scanning-calorimetry (DSC) measurements have been performed on polycrystalline C70. At high temperature, the DSC measurements reveal two phase transitions at 280 and 337 K, respectively. At low-temperatures, the measurements reveal an excess of specific heat with respect to that of graphite, with a classical behavior and a Debye temperature of 145 K. At 50 K a second-order transition is observed.

The spin distribution in a stable nitroxide biradical that shows ferromagnetic interactions in the solid phase has been studied at three levels of theory: First, at the UHF level; then, including correlation effects in UMP2 calculations; and finally, the results are compared with the spin density obtained using the local density functional (LDF) approximation. It is shown that LDF spin densities are closer to UMP2 than to UHF predictions; the difference between the UHF and the (UMP2, LDF) results points to a redistribution of the spin repartition between N and O due to electronic correlation. For planar conformations of the NO group, there is symmetric distribution (D2d) of the spin density on the adamantane skeleton. For nonplanar nitroxides, the molecule is chiral (C2), which results in a breakdown of the spin transmission on part of the adamantane cage.