Theoretical investigation of anion (F⁻, Cl⁻) and cation (Na⁺) interactions with substituted benzene [C₆H₆ − _nY_n(Y = –F, –CN, –NO₂;n= 1–6)]

Abstract

Theoretical studies on anion and cation interaction with a series of substituted benzene molecules [C₆H₆ − _nY_n (Y = –F, –CN, –NO₂; n = 1–6)] is reported in this study. A comparison of energetics at M05-2X/6-31+G* level of theory reveals that with the increase in the size of electronegative group (–F to –CN to –NO₂), the stability of the anion–π and cation–π complexes also increases. The more the electronegative group substitution, the more is the stability of the complex for anion–π systems – in contrast to cation–π complexes where the stability of the complexes decreases with the increase in electronegative group substitution. The effect of basis set superposition error on the interaction energy of benzene-substituted complexes has been analysed. A linear correlation is observed between electron density and charge transfer from ion to the substituted benzene ring in case of anion (F⁻, Cl⁻)–π complexes. Density functional theory–symmetry adapted perturbation theory analysis performed at B3LYP level using 6-31G* and aug-cc-pVDZ basis sets show that the electrostatic and exchange terms contribute more to interaction energy in case of anion–π complexes, whereas polarisation energy contributes more to interaction energy for cation–π complexes albeit in different degrees.