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.

Aromatic nature of neutral and dianionic 1,4-diaza-2,3,5,6-tetraborinine derivatives

“…65 Besides, ACID plot of 4 0 shows that in addition to the ring current over the sixmembered ring, localized currents in the RB-BH fragment signicantly contributes to magnetic anisotropy. These data indicate that even with the same B 4 N 2 -skeletal framework of 6psystem, the index value of each criterion varies depending on the overall charge of the B 4 N 2 systems, 32,33,36 giving rise to the different aromatic nature. 71,72 This study paves a way for the further design and development of aromatic inorganic benzenes.…”

“…Notably, dianionic 4 0 also bears a planar B 4 N 2 ring, which is in stark contrast to the twisted ring framework experimentally observed for 4, implying the impact of substituents at the B and N atoms on the skeletal geometry. 30,[32][33][34][35][36] The selected p-type molecular orbitals (p-MOs) of 3 0 and 4 0 are summarized in Fig. 2.…”

“…The substituent effect on the aromaticity in benzene as well as in borazine has been reported. [30][31][32][33][34][35][36] According to those prior studies, while the aromaticity of benzene resists substituent inuences, that of borazine is signicantly affected by the nature of substituents. In borazine, generally the electron-donating group (EDG) on B decreases the aromaticity, although electron-withdrawing group (EWG) on B and both EDG and EWG on N lead to the pronounced aromaticity.…”

The hidden aromaticity in borazine

“…24 On the other hand, quantification of aromaticity by ring current strength (RCS) calculations suggest that borazine has a weak aromatic behaviour. Several authors 7,24–27 report that the aromaticity of borazine is approximately 28% of the aromaticity of benzene according to RCS, however, their ring current patterns cannot be clearly identified. Other aromaticity criteria also present disagreements.…”

Electronic, optical, and vibrational properties of B3N3H6 from first-principles calculations

“…The thermal decomposition of B 3 N 3 H 6 in unsaturated vapor has been studied [9], showing that the gaseous B 3 N 3 H 6 was decomposed on the reaction vessel surface along with the formation of volatile intermediates. The nature of chemical bond [10], ring current strengths [11], anion-π interactions [12] of B 3 N 3 H 6 were investigated, indicating its wide applications such as active molecule for electrodes [13], reactant for boron nitride nanowalls [14], low-dimensional spin lters [15,16]. etc.…”