Relativistic effects on the ring current strengths of the substituted borazine: B₃N₃H₆ (X=H, F, Cl, Br, I, At)

In this study, we report about the relativistic effects on the aromaticity of borazine, B₃N₃H₆, and their halogenated derivatives (B₃N₃F₆, B₃N₃Cl₆, B₃N₃Br₆, B₃N₃I₆, and B₃N₃At₆), via the magnetically-induced current density method. All-electron density functional theory calculations were carried out using the four-component Dirac-Coulomb hamiltonian, including scalar and spin-orbit relativistic effects. Ring current strengths were obtained by numerical integration over the current flow. These values were compared to the spin-free (scalar relativistic) and nonrelativistic values, to assess the corresponding contributions to aromaticity. It was found that in B₃N₃I₆ and B₃N₃At₆ there exists a significant spin-orbit influence, in line with the expected relativistic effects associated to the heavy elements, iodine, and astatine. Borazine, B₃N₃H₆, is known to be slightly aromatic, but much less aromatic than benzene. The application of an external magnetic field induces a current density, that accounts for the delocalization and mobility of electrons in a molecule. Using this theoretical method, the aromaticity of the derivatives B₃N₃X₆(X = H, F, Cl, Br, I, At) was investigated. The inclusion of heavy elements requires a relativistic treatment where the spin-orbit coupling must be included. The figure shows the three-dimensional pathways of the current density flow in B₃N₃At₆.