High-resolution X-ray diffraction determination of the electron density of 1-(8-PhSC10H6)SS(C10H6SPh-8′)-1′ with the QTAIM approach: evidence for S4 σ(4c–6e) at the naphthalene peri-positions

Abstract

An extended hypervalent S₄ σ(4c–6e) system was confirmed for the linear ^BS-∗-^AS-∗-^AS-∗-^BS interaction in 1-(8-Ph^BSC₁₀H₆)^AS–^AS(C₁₀H₆^BSPh-8′)-1′ (1) via high-resolution X-ray diffraction determination of electron densities. The presence of bond critical points (BCPs; ∗) on the bond paths confirms the nature and extent of this interaction. The recently developed QTAIM dual functional analysis (QTAIM-DFA) approach was also applied to elucidate the nature of the interaction. Total electron energy densities H_b(r_c) were plotted versus H_b(r_c) − V_b(r_c)/2 for the interaction at the BCPs, where V_b(r_c) represents the potential energy densities at the BCP. The results indicate that although the data for an interaction in the fully optimized structure corresponds to a static nature, the data obtained for the perturbed structures around it represent the dynamic nature of the interaction in QTAIM-DFA. The former classifies the interaction and the latter characterises it. Although ^AS-∗-^AS in 1 is classified by a shared shell interaction and exhibits weak covalent character, ^AS-∗-^BS is characterized as having typical hydrogen-bond nature with covalent properties in the region of the regular closed shell interactions. The experimental results are supported by matching theoretical calculations throughout, particularly for the extended hypervalent E₄ σ(4c–6e) (E = S) interaction.