Magnetizabilities of ring-structured molecules, [8]-cyclacene, [8]-BN-cyclacene and [8]-collarene, and their effect on ³He nuclear shielding tensor

The magnetizabilities of three ring-structured molecules, [8]-cyclacene, [8]-BN-cyclacene, and [8]-collarene, were subsequently calculated at the B3LYP/6-31G* level with the CSGT gauge-origin treatment. The magnetizability of [8]-cyclacene shows a large diamagnetic nature in the direction parallel to the ring cylindrical axis, while the value of [8]-BN-cyclacene is nearly isotropic, and that of [8]-collarene is slightly more diamagnetic in the perpendicular direction than in the parallel direction. A large diamagnetic magnetizability in the parallel direction of [8]-cyclacene arises from the current flow around the ring circumference. The magnetic environment in the ring channel of these three molecules was investigated by calculating the nuclear shielding tensor of the ³He atom when the atom moves through the ring channel. The GIAO nuclear shielding tensor changes significantly toward a prolate shape in [8]-cyclacene, but becomes a slightly oblate shape in [8]-BN-cyclacene and [8]-collarene. The changes correlate well with the magnetizabilities of the ring-structured molecules.