Shielding cone behavior in the spherical aromatic He@C606−: origin of the record for the most shielded encapsulated 3He nucleus and comparison to He@C706−
The textbook concept of shielding cone is one of the characteristic properties for planar aromatic species, which explains the nuclear shielding of neighbor molecules located above and below the molecular plane. Here, we explore its resemblance in spherical aromatic fullerenes, where particularly for C606−, it explains the record for the highest shielding observed via 3He-NMR for the endohedral 3He@C606− species. Our results compare the behavior for He@C60 and He@C606− denoting relevant changes in their magnetic response behavior, where an induced shielding cone was observed for the latter with its long-range shielding character. In contrast to planar aromatics which give rise to a shielding cone property only for a perpendicularly oriented field, it was found that the shielding cone in spherical aromatic fullerenes occurs to any orientation. Thus, the orientation dependence behavior of the shielding cone is accounted, unraveling a characteristic shielding cone pattern in He@C606− which further rationalizes its record on the most shielded He nucleus, upon rotation or tumbling from the aromatic ring about the applied field. For the C70 case, the opposite situation has been characterized via 3He-NMR experiments, which is explained in terms of the deshielding/shielding region inside the C70 cage.
Keywords3He-NMR Shielding Shielding cone Spherical aromaticity
The authors acknowledge financial support from FONDECYT 1180638. Part of this work was discussed in QUITEL 2018 meeting, at Santiago de Chile.
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