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The formal redox potentials of electron transfer reactions of fullerene, methanofullerene, fullerene–cyclodextrin complex and methanofullerene conjugates with cyclodextrins in aqueous and dimethylsulfoxide solutions are reported. These new compounds are surface active and retain the redox activity of C60 even in aqueous medium. Compounds have been characterized by an electrochemical admittance technique, which offers an advantage of separating faradaic and capacitive properties. Observed difference of formal redox potentials of the free fullerene forms and their cyclodextrin-containing compounds were used to determine the binding enhancement. Results are interpreted in terms of inter-molecular host–guest interactions of C60-cyclodextrin conjugates.

A Cahn–Ingold–Prelog-like scheme based on edge length allows classification of chiral tetrahedra, free of labels and considered as geometric objects, into left- and right-handed forms, despite the chiral connection between enantiomers. To cite this article: P.W. Fowler, A. Rassat, C. R. Chimie 9 (2006).

In search of a simple internal complexation of C 60 in cyclodextrins, six 2:1 cyclodextrin:[60]fullerene conjugates involving different types of linkers have been synthesised. Using spectrophotometry, laser flash photolysis and pulse radiolysis, we have investigated spectroscopic and photophysical properties of these 2:1 cyclodextrin [60]fullerene monoadduct conjugates ( CDF ), including ground and triplet state absorption spectra, triplet molar absorption coefficients ( e T ), quantum yields of triplet ( Φ T ) and singlet oxygen formation ( Φ Δ ) in water and toluene, in order to probe the possibility of 2:1 inclusion complexes of C 60 between two cyclodextrins. In water, the CDF spectroscopic and photophysical properties indicate hydrophobically driven self-assemblies of the amphiphilic conjugates into spherical micelles with no evidence for the presence of a 2:1 inclusion complex, while in toluene they show no sign of aggregation. It is observed that formation of aggregates in water does not prevent scavenging of HO radical by the C 60 moiety of the CD–C 60 conjugates.

After some remarks about the theoretical foundations of the many-electron Heisenberg–Dirac spin Hamiltonian, we have investigated the transferability of the two-body spin-exchange parameter of this model mapping accurate post-Hartree–Fock results obtained for H2, H3 and H4 systems with the analytical solutions of the corresponding spin Hamiltonian. Highly symmetric structures, described by only one independent spin-exchange parameter, and less symmetric cases, described by two or three spin-exchange parameters have been analyzed. The generalized many-body Heisenberg–Dirac Hamiltonian is found to be suited to reproduce the ab initio values for Hn clusters (n = 2, 3, 4) when internuclear distances are larger that 3 A, i.e., beyond the bonding region. Concerning the transferability of the two-electron spin exchange parameter ( J H 2 ) in this internuclear distance region, particular attention should be paid to the characteristics of the systems analyzed and to their relationship with the parent molecule (here H2), as underlined by the results obtained for H4 square planar system and linear H3 system.

Two novel fullerene[60]-cyclodextrin conjugates have been prepared, they display the highest solubility in water reported to date. This is the first synthesis of such conjugates in which the linker is attached to the secondary rim of β-CD.

We have revealed that the isothermal magnetization M of the genuine organic crystalline dupeyredioxyl ( N , N ′-dioxy-1,3,5,7-tetramethyl-2,6-diazaadamantane; T c (0)=1.48 K) observed below 10 K converges on the S =1 Brillouin function B 1 (( H + λM )/ k B T ) with λ =2.4±0.2 or 2 zJ / k B =3.6±0.3 K, where J and z are, respectively, the averaged exchange interactions and coordination numbers for the S =1 spin system. This fact suggests that S =1 is constructed within a molecule via a strong ferromagnetic coupling between two S =1/2 spins on each of the two NO moieties. The modified notation of the Rushbrooke and Wood theory, T c =2 AzJS ( S +1)/ k B ( A =0.23±0.02 for the three-dimensional Heisenberg systems), is found to quantitatively hold not only for this S =1 spin system but also for other S =1/2 ferromagnets β-phase p -NPNN (2 zJ / k B =3.6 K) and 2,5-DFPNN (2 zJ / k B =2.8 K). Pressure effects of this compound have been studied under the hydrostatic pressure ( P ) up to 15 kbar. T c ( P ) is revealed to show a negative pressure effect with the initial gradient a =d( T c ( P ))/d P =−0.047 kbar −1 , nearly the same value for other organic ferromagnets as β-phase p -NPNN (−0.048 kbar −1 ) and p -Cl-TEMPO radical (−0.03 kbar −1 ), in contrast to the positive pressure effect for genuine antiferromagnets such as TANOL ( a =+0.15 kbar −1 ). Microscopically, different from the above two ferromagnets, the pressure-induced destruction of the orthogonality of molecular orbitals associated with the two NO moieties plays an effective role in reducing the intramolecular ferromagnetic interaction J 0 . The possible weaker intermolecular interactions other than J 0 and J are also expected to be more susceptible to the stress of pressure to result in the reduction of their values perhaps even changing their sign, just as in the case of β-phase NPNN or p -Cl-TEMPO.

The shape space of all possible triangles is represented by a triangular diagram, an analogue of the phase diagram for ternary mixtures. Each point of its interior corresponds to the angle set of a pair of (2D) enantiomeric physical triangles and, with appropriate conventions, to just one member of the pair. Points on median lines represent achiral triangles, those on sides represent degenerate chiral triangles, and those on vertices achiral degenerate linear triangles. A chirality index for triangles must vanish on these lines, but nowhere else within the six compartments of the diagram, and should alternate in sign between them. The archetype is the lowest A2-symmetric eigenfunction of the Schrodinger equation for the particle confined to an equilateral triangular box. Within the constraints, the extrema of an acceptable function may be pushed onto any D3h-symmetric hexagonal set of points in the diagram, thereby verifying a conjecture of Dunitz that any scalene triangle is the most-chiral triangle for some legal 2D-chirality index.

A graph-theoretical procedure is proposed for assigning a chirality descriptor (the topological sign tau(+) or tau(-)) to each enantiomer of a chiral polyhedron, polyhedral molecule or graph, independently of any vertex labelling scheme. Model Cartesian coordinates and rotational strengths are obtained using only adjacency information; a generalised HOMO-LUMO rotational strength is used to associate a sign with a Schlegel diagram and the corresponding three-dimensional structure, polyhedron or molecule. The topological sign gives an unambiguous way of communicating the identity of an enantiomer. The mean-square topological rotational strength is a possible measure of the chirality content of a polyhedral graph or structure.

Three new 2:1 cyclodextrin-fullerene (CD–F) conjugates have been prepared, two β-CD-F (1b and 1c) and one γ-CD–F (1d), of general formula C60[C(COO–X–COOR)2] (1b : X = CH2, 1c, X = CH2CH2OCH2; R = NH-PMBCD (1b,c) or NH–PMGCD (1d), i.e. a β- (1b,c) or γ- (1d) CD, fully methylated except at one primary position, where OH is substituted by NH); they have been compared with the previously described compound 1a (X = (CH2)11, R = NH–PMBCD). The solubility in water at neutral pH of the new molecules is the highest reported to date, greater than 250 mg ml–1. UV and NMR spectra show that aggregates are present in these water solutions. The UV spectra suggest that, at the same concentration of conjugate in water, the percentage of aggregates decreases in the order 1a > 1b ~ 1d > 1c. No evidence of internal complexation of the fullerene moiety by the CD was detected. To cite this article: S. Filippone, A. Rassat, C. R. Chimie 6 (2003) 000–000.

The thermal dissociation of the bisalkoxyamine Download : Download full-size image (denoted StNNSt) releases the styryl St and one of the two isomers of the StNN nitroxide radicals; the former initiates a living chain P and the latter controls the polymerisation by limiting the chain growth. A sequence of dissociation, propagation and recombination reactions produces the StNNP and PNNP bisalkoxyamines as well as a PNN nitroxide. A decomposition side reaction of PNNP leads to HNNP with a hydroxylamine functionality, which by dissociation produces the HNN nitroxide. All these reactions have previously been shown to play a key role in the controlled radical polymerisation of styrene mediated by a dinitroxide biradical [1] , [2] . The evolution of nitroxide radicals in the course of the bulk polymerisation of styrene at 130 °C initiated by StNNSt, has been followed by ESR at this temperature as well as on several samples cooled down from 130 to 21 °C at different time intervals. The hyperfine coupling parameters and the reorientation correlation times have been obtained from the automated fitting of spectra. As the polymerisation proceeds, the StNN radical initially observed is progressively replaced by PNN , characterised by a much longer correlation time, which increases as the chain segmental motion slows down. At high polymer yields (60–80%) the spectra show two components S and F relevant to the slow and fast motional regimes. The S component corresponds to the fraction of PNN embedded in the polymer chain network whereas the F component is assigned to the fraction of PNN moving in free volumes as well as to HNN whose concentration increases till the end of the reaction.

Maps of induced current density are computed with the coupled Hartree–Fock, distributed-gauge, CTOCD-DZ method for the trannulene isomers of the hydrogenated fullerenes C20H10 and C24H12. Orbital analysis identifies ‘in-plane’ ring currents in trannulenes that obey equivalent selection rules to those for conventional annulenes. Thus, in systems of either type, 4-electron diatropicity is associated with electron counts of 4n + 2, 2-electron paratropicity with 4n.

The use of various binitroxides, with both radical sites of similar reactivity, as mediator in the controlled radical polymerization of styrene was examined and the rate constants of the reactions involved were determined at 130 °C. Typical features of a controlled radical polymerization were observed in the early stage of the polymerization, leading to the formation of two-arm macromolecules containing the binitroxide at the core. At higher conversion, however, continuous decomposition reaction resulted in a break of the two-arm macromolecules into a dead chain having an unsaturation end group and a living chain capped by a modified binitroxide. The latter had the free nitroxide site inactivated by conversion into hydroxylamine. The extent of this side reaction was much larger than in classical nitroxide-mediated controlled radical polymerization of styrene. This feature was assigned to the structure of the growing chains. As they contain the binitroxide at the core, the activation reaction produces a pr...

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.

The bulk magnetic properties of the genuine pure organic ferromagnet Dupeyredioxyl ( N , N ′-dioxy-1,3,5,7-tetramethyl-2,6-diazaadamantane, C 12 N 2 O 2 H 20 ) are presented. Magnetization below T c =1.48 K presents no measurable hysteresis, and the anisotropy seems to be due only to crystal shape demagnetization effects. The specific heat presents a nice lambda peak at 1.44 K, and a T 3/2 power law below 1 K that is expected for spin wave excitations in the low T limit. The entropy change due to the phase transition does not give the expected value for two independent spins: 1/2 per molecule. The high-temperature susceptibility presents a Curie–Weiss temperature of 7.0 K. Magnetization curves up to 9 T above T c do not follow a universal behavior with H / T below 50 K. The results are consistent with a model where intramolecular interactions between pairs of the ‘free spins’ form a triplet state well above T c and these S =1 molecules finally order into a true three-dimensional ferromagnetic transition due to intermolecular interactions below 1.5 K.

The stability of toroidal and spherical carbon cage structures, constructed from five- and seven-membered rings, was studied using tight binding, Tersoff and Brenner potential based methods. A special tiling is presented for the torus of minimal strain energy. In order to make comparison between the results of various calculations we defined the σAB square root average bond distance difference between the methods A and B. By addition of six-membered rings to the C40 torus we obtained a toroidal C60 carbon cage molecule. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 136–139, 2001

An efficient, high-yield stereospecific route to three (+/-)-5, 8-disubstituted indolizidines, (209B (I), 209I (II), 223J (III)) and two (+/-)-1,4-disubstituted quinolizidines (207I (IV), 233A (V)), racemates of alkaloids found in the skins of neotropical and Madagascan poison frogs is reported. The structures of the natural alkaloids were thereby established by chiral GC comparison with the exception of indolizidine 209B (I) for which a natural 209B could no longer be detected.

Decagonal C60 crystals grown from n-hexane solutions correspond to an orthorhombic 1:1 solvate (a=10.249 A, b=31.308 A, c=10.164 A). It forms with negative excess volume ( −55.5 A 3 per formula unit) and transforms on heating into fcc C60 (desolvation enthalpy of +50.6 kJ per solvate mole, close to the sublimation enthalpy for pure n-hexane) while n-hexane desorption from fcc C60 is accompanied by an enthalpy of +48.6 kJ per solvent mole. Thus solvate formation is preferred to solvent adsorption. Orthorhombic C 60 ·1 n -hexane undergoes no degradation when stored in air for 9 years at room temperature in the dark.

It is shown how Paul Villard's chemical interests guided him in his studies of cathode rays, X rays and radium rays. His experiments in radioactivity led to the unexpected discovery of gamma rays in 1900.

If a fullerene is defined as a finite trivalent graph made up solely of pentagons and hexagons, embedding in only four surfaces is possible: the sphere, torus, Klein bottle, and projective (elliptic) plane. The usual spherical fullerenes have 12 pentagons; elliptic fullerenes, 6; and toroidal and Klein-bottle fullerenes, none. Klein-bottle and elliptic fullerenes are the antipodal quotients of centrosymmetric toroidal and spherical fullerenes, respectively. Extensions to infinite systems (plane fullerenes, cylindrical fullerenes, and space fullerenes) are indicated. Eigenvalue spectra of all four classes of finite fullerenes, are reviewed. Leapfrog fullerenes have equal numbers of positive and negative eigenvalues, with 0, 0, 2, or 4 eigenvalues zero for spherical, elliptic, Klein-bottle, and toroidal cases, respectively.

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.

Quenching with tert -butyl nitroso 2-lithio-4- tert -butyl toluene prepared by an exchange reaction with t -butyl-lithium, followed by acidic hydrolysis furnishes in good yields the corresponding aromatic hydroxylamine whose oxidation affords the nitroxide, N -(2-methyl-5- tert -butyl-phenyl)- N - tert -butyl-nitroxide. This nitroxide did not undergo decomposition after heating 17 h in solution at 105 °C.

An invivo biotransformation of [60] fullerene is observed that does not follow a usual redox metabolic pathway. Following the administration of a single dose of micronized C60 to Swiss mice, C60-retinol and retinyl palmitate adducts were identified in liver by UV/VIS spectroscopy and mass spectrometry after high performance liquid chromatography. NMR investigations of the main biotransformed compound, after invitro synthesis, show cycloaddition of retinol to C60. The observed biotransformation, which proves that C60 does not remain unchanged in the liver as believed previously, also shows that Diels–Alder-like reactions can occur invivo.

It has been shown by experimental and theoretical studies that exchange interactions in non planar π systems are strongly dependent on the geometrical parameters characterizing the non planarity. A study of the exchange interaction in isolated nitroxide biradicals is presented for non planar paraphenylene bis nitroxide 3 [1,4-di-t-butyl-2,5-bis(t-butylaminoxyl) benzene (anti)], non planar metaphenylene bis nitroxides 7 and planar metaphenylene bis nitroxide 9. Determination of positive or weak negative exchange interactions in isolated molecules in dilute solution is difficult and can be inaccurate. 3 is a ground state singlet 2J/k = −35K. Metaphenylene bis nitroxide 7g [1-t-butyl,3,5-bis(t-butylaminoxyl) benzene] and 9 [1,2,9-tetrahydro 2,2,4,4,6,6,8,8-octamethyl-4H,6H-benzo[1,2d; 4,5[dcirc]]bis(1,3 oxazine)-1,9 dioxyl] are probably ground state singlets, the tripletsinglet separation being smaller than 10K, contrary to theoretical predictions. X-Ray structure of 7a A [1,3,5-trimethyl-2,6-bis(t-...

A fullerene-like ball is found in a second century mosaic from Porta Marina Roman Baths near Ostia. Although it could be an hexadecahedral ball (28 vertices, 4 hexagonal and 12 pentagonal faces), it is probably an erroneous representation of a dodecahedral ball.

The 2,5-di-tert-butyl-3,4-dimethoxycarbonyl-pyrryloxyl radical has the small est line-width and the smallest nitrogen hyperfine splitting reported for a stable nitroxide. The influence of long range proton splittings was shown by selective and total deuteriation. As expected on theoretical grounds, line widths and nitrogen hyperfine splitting are correlated.

High amounts of micronized C60 have been injected intraperitoneally into Swiss mice. Until the fourteenth day, they were still alive without any behaviour trouble. C60 was well absorbed, and found localized in spleen and liver. Inside the liver, C60 was

The point-group representations spanned by the vertices, edge vectors, face circulations and cell centres of a wide variety of multi-shelled polyhedral structures are related in a simple equation that generalises the well known Euler and Schlafli theorems. The new theorem can be expected to have applications in spectroscopic and electronic structure theory of a large class of clusters and coordination polyhedra.

1,4-Bis(4‘,4‘-dimethyloxazolidine-N-oxyl)cyclohexane (1), a “fast exchange” biradical in which the principal directions of the g and D tensor are different, has been studied by ESR at low temperature at 245 and 294 GHz. These frequencies correspond to an “intermediate high field” (δgμBB ≈ |D|), i.e., such that the powder spectrum is neither dominated by the anisotropy of the g tensor (as at “very high field”) nor by that of the dipolar D tensor (as at “low field”). As B increases from low field to very high field, the canonical directions do not simply rotate from the principal directions of D to those of g but split into “pseudocanonical directions” at intermediate fields. The principal values of the magnetic tensors and their relative orientations were obtained by computer simulation. They are more accurate for the g tensor than those determined at low field; the dipolar parameter D is negative. Magnetization and ESR studies show that 1 is a ground-state singlet with an exchange interaction 2J/k = −25 ±...

The ESR spectra of the bis(2,2,6,6-tetramethyl-4-piperidinol-1-oxyl) adipate biradical at several temperatures in ethanol solution were simulated, taking into account all allowed conformers corresponding to the rotational isomerism model. The probabilities of these conformers, not accessible by ESR, were derived from 13C spin relaxation measurement on the diamagnetic reduced form of the biradical. The least-squares fits of ESR spectra provided the temperature dependence of the rates of internal motions and of the tumbling correlation time of the biradical and also an estimate of the electron spin exchange parameters.

A nitroxide biradical 2,6-dioxy-2,6-diaza-1,1,3,3,5,5,7,7-octamethyldicyclopentano[b;e]pyridine (1) and the corresponding monoradical (2-oxy-6-hydroxy) were prepared starting from 2,2,5,5-tetramethyl-3-oxopyrrolidine by successive condensation with formaldehyde (KOH) or DMF (K in THF), NH4OAc and oxidation (Na2WO4-H2O2). In ethanol, biradical 1 shows a quintet (|J| ≫ |aN| = 14.6 G). In frozen ethanol solution, the experimental spectra (X-band at 120 K and 240 GHz at 7, 15 and 25 K) can be computer simulated with the following parameters: D = −64 G; E = 1 G; gxx = 2.0093; gyy = 2.0064; gzz = 2.0020; Axx = Ayy = 8 G; Azz = 32.2 G. From the temperature dependence of the high-field spectra, D is found to be negative.

Crystallographic and thermodynamic experiments show that crystalline C60 obtained by slow evaporation of solutions in n-heptane is a C60, n-heptane 1:1 solvate. Its lattice is hexagonal, Laue class 6/mmm, with a = 10.00(4) A and c = 10.16(1) A. No transition is observed at temperatures higher than 100 K, and desolvation into fcc C60 occurs at about 360 K with ΔH = +43.5 J g−1, close to the sublimation enthalpy for pure n-heptane. Another binary compound, presumably a polymorph of the former, is sometimes obtained by rapid evaporation of toluene + n-heptane mixtures. Its lattice is orthorhombic, Immm, with a = 10.07 A, b = 10.22 A and c = 48.9 A.

Self-consistent Field and M011er Plesset calculations have been carried out for convex spheroalkanes (CH) 10 represented by simple trivalent graphs, using Balaban's classification. Their exact symmetries, i.e. C s , C 2 , C 2v , C 3v and D 5 , have been determined as well as their relative stabilities. The latter are in accordance with the energy balance of appropriate isodesmic reactions. Their theoretical values are sensitive to the quality of the atomic sets employed to describe both inner and valence shells of the various isomers. rather than to the approximation level of the theory (SCF versus MP2). In the Appendix, selected bond lengths, bond angles and dihedral angles are presented.

La visualisation de molecules du fullerene C 84 adsorbees sur une surface d'or est presentee. La preparation de l'echantillon par evaporation d'une solution et l'etude par STM ont ete effectuees a l'air. Les vues montrent des details intra moleculaires.

In order to check its possible acute toxicity, C60 was incorporated into living human phagocytes. It was observed that C60 has no influence on the survival of human leukocytes.

New experimental data on the vibrational spectrum of C60 have been recorded with neutron inelastic scattering (NIS). These data modify the positions of the lattice modes, which previously were reported at too high frequencies. New information on the frequencies of the intramolecular modes has also been obtained using a better instrumental resolution.

Raman spectra of C60 fullerite at pressures up to 37 GPa with shear deformation are studied. We have found two states at high pressures, that persist after pressure release and have various transparencies in the near IR region. The nontransparent state is formed at 6–18GPa and has a Raman spectrum with broadened bands at frequencies close to those of the initial fullerite. The transparent state was obtained at pressures higher than 18GPa, and the Raman bands are broadened and overlapping in comparison with those of the nontransparent state. We suppose that C60 molecules persist in both states. The transparent state of fullerite shows a hardness higher than that of diamond.

On presente dans cet article la construction graphique de la formule plane des plus petits spheroroalcanes (molecules (CH) n , N pair, dont la formule plane est un graphe plan trivalent simple), qui ont la symetrie topologique (plus haute symetrie possible que peut avoir la molecule sans tenir compte de son energie) de n'importe quel groupe de symetrie a point fixe (a nombre fini d'elements) de l'espace. On condidere d'abord les groupes de symetrie a point fixe du plan et on montre que l'on peut utiliser les lettres Γ et Δ pour materialiser ces groupes

International audience; Opticafiy pure bicyclo(3.3.0]oc~-Z,6-dione is easily obtained with a yield of 4% for each enantiomerfrom 1,5-cyolooctadiene 5 steps, by resolution of the intermediate diol wth menthyloxyacetiacid. Its CD is60 % larger than twice the CD of a coresponding monoketone dicatingi indicating interactions between non-conjugatedchromophores

A 3.89 mg single crystal of fullerene C60 was grown by sublimation and its thermodynamic properties were determined through DSC measurements. The transition temperature and enthalpy are the highest ones that were ever measured (Ttr = (261.4 ± 0.5) K and ΔtrH = (9.0 ± 0.5) kJ mol-1, respectively) and are thought to be near-standard ones. However, it is shown that mechanical grinding smears out the DSC transition peak. Constraints which develop along free (111) surfaces are assumed to be responsible for this phenomenon.

Fluorination of pure C60 and a C60/C70 mixture has been studied under different experimental conditions: reaction time, temperature, fluorine pressure. The products obtained have been characterized by IR and NMR spectroscopy, X-ray diffraction, and mass spectrometry analysis by positive and negative ions.

A well-developed surface of a decagonal C 60 crystal grown from n -hexane has been imaged directly by STM with molecular resolution. Fairly regular patterns have been obtained over large surface areas. However, no internal structure of individual carbon molecules could be observed. This means that some orientational motion persist in the molecular packing of the decagonal crystal as also demonstrated in cubic C 60 crystals.

X-ray diffraction and thermodynamic measurements show that crystalline fullerene C70 obtained from toluene solutions is a C70, toluene 1:1 solvate. Its structure is orthorhombic with space group Pbca (a = 21.075 A, b = 32.990 A, c = 10.844 A). The evolution of this solvate towards the face-centred cubic and hexagonal phases of pure C70 is described and a hierarchy of relative stabilities of these latter phase is tentatively proposed.

In order to test the isotope effect in the superconducting doped fullerenes, we made the K 3 C 60 compound in which the C 60 molecules are enriched in 13 C. The 13 C concentration in C 60 powder, as determined by mass spectrometry, was found to be 82%. A standard sample K 3 12 C 60 was prepared in the same conditions. The superconducting transition was measured on both samples by an ac susceptibility technique. The onset transition temperature observed at T c = 19.6±0.1K for the standard sample is lowered by 1.8K in the 13 C compound which leads to α ≈ 1.45±0.3 in the usual BCS formula T c ∼ M − α . From 13 C NMR measurements of the relaxation time T 1 on these two compounds, the isotopic shift leads to α ≈ 1.1±0.3 in a magnetic field of 9.4T, which remains strongly higher than the theoretical value α = 0.5.

We report the temperature and pressure dependence of 13 C nuclear spin-lattice relaxation time T 1 on K 3 C 60 in the normal state. Within the BCS electron-phonon pairing mechanism, we estimate the coupling strength and the relevant phonon mode involved to account for superconductivity.

Recent studies carried out on an organic superconductor, s-(BEDT-TTF) 2 I 3 , have shown the important role played by the 13 C isotope on the T c transition, when substitution is made on the central CC bond of the molecule. Simultaneously, Raman studies determined the frequency shifts observed in the CC stretching vibrations in the substituted samples and consequently, put in evidence the role of the intramolecular Ag vibrations. We have extended these studies to compounds of the new carbon family, the fullerenes, in which 82% of the carbon atoms were substituted with 13 C in C 60 . The superconducting transition measured on the same sample doped with potassium is lowered by 1.5 to 2K as compared to the standard material doped in similar conditions. In the Raman spectrum, the main Ag band measured at 1467 cm −1 in 12 C 60 is shifted to 1420 cm −1 in enriched 13 C 60 . Taking into account the ratio between the molecular weight of the enriched 13 C 60 and of the standard material, one predicts a theoretical value for this mode at 1418 cm −1 in the enriched sample. A preliminary analysis of the Raman spectrum will be presented.

We report the pressure and temperature dependences of 13C nuclear spin-lattice relaxation time T1 in the normal state of K3C60. From the 1/T1T temperature and pressure profiles, a Fermi-liquid theory is used to investigate the variation of the density of states and the amplitude of electron-electron interaction. Finally the results obtained are shown to support a pairing mechanism for superconductivity that would involve high-frequency modes.