Global and Local Shielding/Deshielding Variation in C₆₀ and C₇₀ Fullerenes Upon Reduction: Evaluation of Aromaticity, ¹³C‐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 ¹³C-NMR patterns in C₆₀ and C₇₀ 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 σ₃₃ (or δ₃₃) shielding component under the principal axis system (PAS) of the chemical shift anisotropy (CSA) at the representative carbon nucleus. For C₆₀ ^6- a shielding cone property is enabled from any orientation, accounting for a significant spherical aromatic character. In contrast, in C₇₀ ^6-, 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 C₆₀ and C₆₀ ^6-, with a continuous anisotropic outer contour for the latter. In contrast, C₇₀ and C₇₀ ^6- 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.