Dynamic and static behavior of the H... pi and E... pi interactions in EH sub(2) adducts of benzene pi -system (E = O, S, Se and Te), elucidated by QTAIM dual functional analysis

Dynamic and static behavior of the interactions in the EH sub(2) adducts of a benzene pi -system (E = O, S, Se and Te) is elucidated by applying QTAIM-DFA (QTAIM dual functional analysis). Two types of H-*- pi and E-*- pi interactions are detected in the adducts, where the asterisk (*) emphasizes the existence of the bond critical point (BCP) on the interaction in question. Total electron energy densities H sub(b)(r sub(c)) are plotted versus H sub(b)(r sub(c)) - V sub(b)(r sub(c))/2 [=( super(2)/8m)(grad) super(2) rho sub(b)(r sub(c))] at BCPs in QTAIM-DFA, where V sub(b)(r sub(c)) are the potential energy densities at BCPs. Data from the fully optimized structures are analyzed by polar (R, [thetas]) coordinate representation. Each plot for an interaction, containing data from the perturbed structures with those of the fully optimized one, shows a specific curve, which provides important information. The plot is expressed by ([thetas] sub(p), Kappa sub(p)): [thetas] sub(p) corresponds to the tangent line for the plot and Kappa sub(p) is the curvature. [thetas]and [thetas] sub(p) are measured from the y-axis and y-direction, respectively. Moreover, (R, [thetas]) corresponds to the static nature, ([thetas] sub(p), Kappa sub(p)) represents the dynamic nature of interactions. While [thetas]classifies the interaction in question, [thetas] sub(p) characterizes it. Both values are less than 90 degree for all H-*- pi and E-*- pi interactions examined in this study; therefore, they are all classified by the pure closed-shell interactions and predicted to have the character of vdW nature. However, it is suggested that E-*- pi has the nature of the stronger interaction than the case of H-*- pi for dynamic behavior in the same species evaluated at the MP2 and M06-2X levels. The nature of the interactions is well analyzed and specified by applying QTAIM-DFA.