High-resolution X-ray diffraction determination of the electron density of 1-(8-PhSC 10 H 6 )SS(C 10 H 6 SPh-8')-1' with the QTAIM approach: evidence for S 4 σ(4c-6e) at the naphthalene peri -positions.

An extended hypervalent S 4 σ(4c-6e) system was confirmed for the linear B S-∗- A S-∗- A S-∗- B S interaction in 1-(8-Ph B SC 10 H 6 ) A S- A S(C 10 H 6 B SPh-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 A S-∗- A S in 1 is classified by a shared shell interaction and exhibits weak covalent character, A S-∗- B 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 4 σ(4c-6e) (E = S) interaction.