Relativistic effects on the aromaticity of the halogenated benzenes: C₆X₆, X = H, F, Cl, Br, I, at

In this study we report about the relativistic effects on the aromaticity of the six hexahalogenated compounds (C₆H₆, C₆F₆, C₆Cl₆, C₆Br₆, C₆I₆ and C₆At₆), via a magnetically induced current density method. All-electron density functional theory (DFT) calculations were carried out using the four-component Dirac-Coulomb (DC) Hamiltonian, including scalar and spin-orbit (SO) relativistic effects. Fully relativistic values of the magnetically induced ring currents were obtained by numerical integration over the current flow. These values were compared to the spin-free (SO interaction switched off) and non-relativistic values, in order to assess the corresponding contributions to aromaticity. It was found that in C₆I₆ and C₆At₆ there is a strong SO influence, in line with the expected relativistic effects of the heavy elements, iodine and astatine.