Nature of S2Se2 σ(4c–6e) at naphthalene 1,8-positions and models, elucidated by QTAIM dual functional analysis

Abstract

The nature of extended hypervalent interactions of the ^BE–*–^AE–*–^AE–*–^BE type is elucidated for 1-(8-Me^BEC₁₀H₆)^AE–^AE(C₁₀H₆^BEMe-8′)-1′, (1 (^AE, ^BE) = (S, S), 2 (S, Se), 3 (Se, S) and 4 (Se, Se)) and models A–D, ^BR₂^BE⋯(^AR)^AE–^AE(^AR)⋯^BE^BR₂ (^AR, ^BR = H and Me). QTAIM dual functional analysis, which we proposed recently, is applied to the analysis. Total electron energy densities H_b(r_c) are plotted versus H_b(r_c) − V_b(r_c)/2 for the interactions at bond critical points (BCPs; *), where V_b(r_c) show potential energy densities at BCPs. Data for the perturbed structures around the fully optimized structures are employed for the plots, in addition to those of the fully optimized ones. While the data for the fully optimized structures are analysed by the polar coordinate (R, θ) representation, those containing the perturbed structures are by (θ_p, κ_p): θ_p corresponds to the tangent line for the plot and κ_p is the curvature. While (R, θ) show the static nature, (θ_p, κ_p) represent the dynamic nature of interactions. All ^AE–*–^AE interactions in 1–4 and models A–D are classified by the shard shell interactions and have the character of a weak covalent nature. The ^AE–*–^BE interactions in 1–4 are all classified by the regular closed shell interactions. They are predicted to have the typical HB (hydrogen bond) nature with covalency for 1 and 2 but the nature of the molecular complex formation through CT for 3 and 4. The ^AE–*–^BE interactions in models A–D are predicted to be weaker than those in 1–4.