Vibrational spectra of C60C8H8 and C70C8H8 in the rotor-stator and polymer phases

C60-C8H8 and C70-C8H8 are prototypes of rotor-stator cocrystals. We present infrared and Raman spectra of these materials and show how the rotor-stator nature is reflected in their vibrational properties. We measured the vibrational spectra of the polymer phases poly(C60C8H8) and poly(C70C8H8) resulting from a solid state reaction occurring on heating. Based on the spectra we propose a connection pattern for the fullerene in poly(C60C8H8), where the symmetry of the C60 is D2h. On illuminating the C60-C8H8 cocrystal with green or blue light a photochemical reaction was observed leading to a similar product to that of the thermal polymerization.Comment: 26 pages, 8 figures, to appear in Journal of Physical Chemistry B 2nd version: minor changes in wording, accepted version by journa

Investigations of N@C60 and N@C70 stability under high pressure and high temperature conditions

Endohedral fullerenes encapsulating single nitrogen atoms (N@C60 and N@C70) are spin active, due to the presence of unpaired nitrogen electron spins. High reactivity of nitrogen leads to a poor stability of these molecules at elevated temperatures, drastically restricting possibilities of their chemical treatment. In this study, N@C60 and N@C70 in toluene solutions were subjected to high pressure (HP) up to 0.8 GPa and annealed for 1, 2, 10 or 24 h, at either room or elevated temperatures. In each case the number of surviving molecules was evaluated based on the relative spin counts of ex situ EPR spectra obtained before and after the treatment. The enhanced thermal stability of N@C60 and N@C70 under HP conditions is attributed to inhibited formation of azabridges, which under normal pressure facilitate the escape of nitrogen from the fullerene cage. © 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

Reversible nano-scale phase separation of Rb 4 C 60 under pressure. Reversible Nano-Scale Phase Separation of Rb 4 C 60 under Pressure

Abstract. The alkali fulleride Rb 4 C 60 has been investigated by studies of the resistance and by Raman spectroscopy under pressures up to 2 GPa and 13 GPa, respectively. Our data show a reversible phase separation into metallic Rb 3 C 60 and Rb 6 C 60 at pressures above 1 GPa. The reversibility indicates that the phase separation primarily occurs on the nanometer length scale. The data explain several puzzling results reported in the recent literature. Introduction The alkali metal fullerides show fascinating structural and transport properties related to charge transfer from alkali metal (A) to fullerenes. Among A 4 C 60 materials, light alkali compounds (A = Li, Na) form interfullerene covalent bonds and thus doped fullerene polymers The results from earlier studies of Rb 4 C 60 under pressure seem incompatible. NMR data suggested an insulator-to-metal transition at 0.8 GP

Discriminated structural behaviour of C60 and C70 peapods under extreme conditions

cited By 15International audienceWe studied structural changes in C60 and C70 peapods - i.e. C60 and C70 chains inserted inside single-walled carbon nanotubes - when submitted to high pressure and temperature conditions. X-ray diffraction experiments showed that while C60 molecules polymerize inside nanotubes at pressures and temperatures consistent with polymerization in bulk C60 phases, no polymerization is observed in C70 peapods, even at pressures and temperatures above the threshold for polymerization in bulk C70. Tubular confinement in the nanotube container prevents the monomers to rearrange in the way needed for polymerization. This result testifies for the strong influence of confinement on the behaviour of C70

Endohedral metallofullerenes in self-assembled monolayers.

A method has been developed for the attachment of a dithiolane group to endohedral metallofullerenes via a 1,3-dipolar cycloaddition reaction. This sulfur-containing functional group serves as an anchor, enabling efficient immobilisation of endohedral fullerenes on Au(111) surfaces at room temperature, directly from the solution phase. The functionalised fullerenes form disordered monolayers that exhibit no long-range ordering, which is attributed to both the strong bonding of the dithiolane anchor to the surface and to the conformational flexibility of the functional group. Endohedral fullerenes Er(3)N@C(80) and Sc(3)N@C(80) have been used as models for functionalisation and subsequent surface deposition. Their chemical reactivity towards dithiolane functionalisation and their surface behaviour have been compared to that of C(60). The endohedral fullerenes appear to be significantly less reactive towards the functionalisation than C(60), however they bind in a similar manner to a gold surface as their dithiolane terminated C(60) counterparts. The optical activity of Er(3)N@C(80) molecules is preserved after attachment of the functional group. We report a splitting of the endohedral Er(3+) emission lines due to the reduction in symmetry of the functionalised fullerene cage, as compared to the highly symmetrical icosahedral C(80) cage of pristine Er(3)N@C(80)

Orientational Ordering and Intermolecular Interactions in the Rotor-Stator Compounds C-60 center dot C8H8 and C-70 center dot C8H8 Studied under Pressure

Pressure-dependent transmittance measurements on C-60 center dot C8H8 and C-70 center dot C8H8 at room temperature were performed for pressures up to 10 GPa in the mid- and near-infrared frequency range, in order to monitor the vibrational modes of the fullerene and cubane molecules as a function of external pressure. Furthermore, the position of the absorption edge related to intramolecular electronic excitations on the fullerene molecules was studied with increasing pressure. For C-60 center dot C8H8, the anomaly at 0.5 GPa in the pressure dependence of the vibrational modes indicates a pressure-induced orientational ordering transition of the fullerene molecules and the anomaly at 1.3 GPa can be related to fullerene-cubane interaction. In C-70 center dot C8H8, the pressure-induced changes are more pronounced, with a splitting of the cubane modes at the pressures 0.8 and 1.75 GPa. This finding indicates stronger intermolecular interactions in C-70 center dot C8H8 compared to C-60 center dot C8H8, leading to larger distortions of cubane molecules. The energy position of the absorption edge in C-60 center dot C8H8 and C-70 center dot C8H8 shows a nonlinear decrease with increasing pressure. The zero-pressure value of the absorption edge in C-60 center dot C8H8 is larger than that of pristine C-60 indicating that the cubane molecules reduce the overlap of the C-60 molecular orbitals. In C-70 center dot C8H8, no shift of the optical absorption edge relative to C-70 is found, in agreement with this compound being closer to a host-guest system than C-60 center dot C8H8