Relativistic effects on the ring current strengths of the substituted borazine: B ₃ N ₃ H ₆ (X=H, F, Cl, Br, I, At)

In this study, we report about the relativistic effects on the aromaticity of borazine, B ₃ N ₃ H ₆ , and their halogenated derivatives (B ₃ N ₃ F ₆ , B ₃ N ₃ Cl ₆ , B ₃ N ₃ Br ₆ , B ₃ N ₃ I ₆ , and B ₃ N ₃ At ₆ ), 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 B ₃ N ₃ I ₆ and B ₃ N ₃ At ₆ there exists a significant spin-orbit influence, in line with the expected relativistic effects associated to the heavy elements, iodine, and astatine. Borazine, B ₃ N ₃ H ₆ , 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 B ₃ N ₃ X ₆ (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 B ₃ N ₃ At ₆ .