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.