NMR investigation of the electronic structure of the RbC60 polymer phase

Sensitive absorptive refocused scalar correlation NMR spectroscopy in solids

A new two-dimensional NMR experiment is described which is suitable for obtaining magic angle spinning (MAS) scalar correlation spectra in solids. The new experiment has several advantages, including increased cross peak intensities, coupled with good suppression of the diagonal. Its utility is demonstrated via assignments of the carbon-13 MAS spectra of progesterone at natural abundance and of the polymer phase of 50%-U-13C-CsC60.

Solid-State NMR Study of Na versus K Doping of para-Phenylene Oligomers

13C solid-state nuclear magnetic resonance (NMR) experiments were performed on p-terphenyl, p-quaterphenyl, and p-sexiphenyl either in their pristine or doped with alkali metals form. The 13C NMR spectra of doped materials show new resonances by comparison with pristine compounds. For the K-doped materials, these resonances appear in the 90-135 ppm range, while for Na-doped materials, they are observed in the larger 20-150 ppm range. It suggests that the interaction between the alkali ions and the oligomers depends on the nature of the alkali. It is corroborated by 13C NMR experiments after exposure to air that show different behaviors. As expected, air exposure of K-doped samples restores the pristine spectra. This is not the case for Na doping, where the signature of the doped material persists even after exposure to air. In the latter case, some 13C resonances can be assigned to sp3 hybridized carbons and to the quinoid group. It suggests that Na doping induces a polymerization of the oligophenylenes.

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.

COMPUTATIONAL APPROACH TO THE PHYSICAL CHEMISTRY OF FULLERENES AND THEIR DERIVATIVES

A critical review is presented of results obtained with different computational methods (mainly ab initio) on C60, C70, and specific fullerene derivatives, also in comparison with experimental data. From the discussion of diverse systems, the (often underestimated) complexity of their physical and chemical behavior emerges, and hence the importance of an accurate description and the need for a careful inspection of the experimental data, with which comparison is often intrinsically difficult. The ambition of this review is to help establish a basis not only for a nonsuperficial reading of the existing literature, but also for a constructive approach with computations to the challenge posed by recent promising applications of fullerenes in nanotechnology, optoelectronics, and biology.