of silica gel using 20 % CH 2 Cl 2 /hexane as eluant. The best fractions were pooled, evaporated, and recrystallized twice from chloroform/ acetonitrile to yield 12.2 g (23 %) of the title compound as off-white crystals, mp 178±181 C [11].

The temperature-dependent frequency shift of resonant Raman spectra of double-wall carbon nanotubes is investigated in the range of 78–650 K. We show here that different radial breathing mode (RBM) peaks, which are relative to different tube diameters, have a different temperature coefficient of frequency shift, and the larger diameter carbon nanotubes have more RBM frequency downshift with increasing temperature. We attribute the RBM frequency variation to the temperature dependence of the stretching force constant of C–C bond.

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Resonant Raman scattering (RRS) spectra of individual carbon nanotubes on a SiO2 substrate have been investigated first in the temperature range of 100-600 K (Phys. Rev. B 2002, 66, 115411). It was revealed by the intensity abnormality of the radial breathing mode (RBM) that the carbon nanotubes have a temperature-dependent density of electronic states. This means that the previously reported temperature coefficients of RBM of carbon nanotubes are smaller than their "real" ones for the bulk samples of single- or double-walled carbon nanotubes. Comparatively, the G line of individual nanotubes shows no observable difference relative to the bulk samples.

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