Global and Local Shielding/Deshielding Variation in C and C Fullerenes Upon Reduction: Evaluation of Aromaticity, C-NMR and Anisotropy Patterns.

Fullerenes are statically pleasant species featuring symmetric cages, which can be modified upon reduction. Here, we theoretically account for the variation of C-NMR patterns in C and C upon six-fold reduction and the overall variation of the enabled shielding/deshielding regions induced by π and σ electrons according to different orientations of the external field and the related anisotropy. Our results show a significant modification of the chemical shift given by the main variation of the σ (or δ) shielding component under the principal axis system (PAS) of the chemical shift anisotropy (CSA) at the representative carbon nucleus. For C a shielding cone property is enabled from any orientation, accounting for a significant spherical aromatic character. In contrast, in C , a shielding cone is reserved only for an axial-oriented field, with a deshielding cone behavior obtained from the complementary equatorial orientations. The overall anisotropy shows an inner isotropic region for C and C , with a continuous anisotropic outer contour for the latter. In contrast, C and C both show larger anisotropies, given the lesser spherical shape in addition to the modified π-surface. Such information is useful for further rationalizing the implementation of magnetic anisotropic molecular devices into fullerene-based materials.