Quantifying electron delocalization in orthogonal channels: Theoretical investigation of σ and π aromaticity in [C6I6]2+ and [C6Cl6]2+

The unique properties of the hexaiodobenzene dication are analyzed by the means of density functional theory and compared to those of the analogous hexachloro compound. [C6I6]2+ is fulfilling the Hückel (4n + 2) rule for both its π and σ electrons, so that two orthogonal channels are opened for electron delocalization. This molecule has been chosen as the simplest prototype to set up a computational protocol to study and quantify delocalization at the periphery of a benzene core. We demonstrate that electron delocalization can be quantified by analyzing the variation of both magnetic shielding tensors and of nucleus independent chemical shift.