Comparative Investigation on Non-IPR C68 and IPR C78 Fullerenes Encaging Sc3N Molecules

Abstract

A computational study on the experimentally detected Sc₃[email protected]₆₈ cluster is reported, involving quantum chemical analysis at the B3LYP/6-31G* level. Extensive computations were carried out on the pure C₆₈ cage which does not conform with the isolated pentagon rule (IPR). The two maximally stable C₆₈ isomers were selected as initial Sc₃[email protected]₆₈ cage structures. Full geometry optimization leads to a confirmation of an earlier assessment of the Sc₃[email protected]₆₈ equilibrium geometry (Nature2000, 408, 427), namely an eclipsed arrangement of Sc₃N in the C₆₈ 6140 frame, where each Sc atom interacts with one pentagon pair. From a variety of theoretical procedures, a D_3h structure is proposed for the free Sc₃N molecule. Encapsulated into the C₆₈ enclosure, this unit is strongly stabilized with respect to rotation within the cage. The complexation energy of Sc₃[email protected]₆₈ cage is found to be in the order of that determined for Sc₃[email protected]₈₀ and exceeding the complexation energy of Sc₃[email protected]₇₈. The cage−core interaction is investigated in terms of electron transfer from the encapsulated trimetallic cluster to the fullerene as well as hybridization between these two subsystems. The stabilization mechanism of Sc₃[email protected]₆₈ is seen to be analogous to that operative in Sc₃[email protected]₇₈. For both cages, C₆₈ and C₇₈, inclusion of Sc₃N induces aromaticity of the cluster as a whole.