High-resolution X-ray diffraction determination of the electron density of 1-(8-PhSCH)SS(CHSPh-8')-1' with the QTAIM approach: evidence for S σ(4c-6e) at the naphthalene -positions.

An extended hypervalent S σ(4c-6e) system was confirmed for the linear S-∗-S-∗-S-∗-S interaction in 1-(8-PhSCH)S-S(CH SPh-8')-1' (1) 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 ( ) were plotted ( ) - ( )/2 for the interaction at the BCPs, where ( ) 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 S-∗-S in 1 is classified by a shared shell interaction and exhibits weak covalent character, S-∗-S 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 E σ(4c-6e) (E = S) interaction.