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

Abstract

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.