Theoretical study of borazine: cation–π (Be²⁺, Mg²⁺, and Ca²⁺) interaction

Abstract

The geometries of the complexes of Be²⁺, Mg²⁺, and Ca²⁺ metal cations with borazine ring were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d,p) basis set. Then, the interaction energies corrected by basis set super position error were calculated in the same level. The results show that interaction energy is strongly dependent on the charge-to-size ratio of the cation. Therefore, Be²⁺ cation has the most interaction energy value with respect to Mg²⁺ and Ca²⁺ metal cations. Natural bond orbital analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules was also applied to analyze the properties of the bond critical points (CPs) (electron densities and their Laplacians) involved in the coordination between borazine ring and the metal cations. There are also some important correlations between the interaction energies, the electron densities (ρ(r)), and the Laplacian of the densities (∇²ρ(r)) in (3, +3) CPs with the equilibrium distance from cation to the geometric center of the ring (R _e). Finally, nucleus-independent chemical shift method is also used for calculation of aromaticity values of borazine ring and its complexes.