Double aromaticity of the B40 fullerene: induced magnetic field analysis of π and σ delocalization in the boron cavernous structure

Abstract

The induced magnetic field of B₄₀ was dissected into contributions from π, σ and core electrons revealing the origins for the formation of the strong long range shielding response characterizing the spherical aromatic nature of the cavernous D_2d structure. Our analysis showed the complementary role of π and σ orbitals for the formation of the global shielding cone, with weak π contributions at a long range and strong σ contributions inside the cage, supporting the molecule as double aromatic with weak π and strong σ delocalization. Similar local variations of both π and σ magnetic responses were identified portraying peripheral diatropic and local paratropic currents. The weak π aromaticity is explained on the basis of symmetry rules pertaining to its electronic structure which forbid small gap paratropic rotational excitations.