Relationship between geometry and energy of interactions in S8 dimers

Abstract

Elemental sulfur exists in several allotropes, including α-S8, β-S8, and γ-S8, wherein the arrangement of cyclic S8 molecules varies according to the specific allotrope. Intermolecular interactions among S8 molecules have been detected within crystal structures extracted from the Cambridge Structural Database (CSD) and the Inorganic Crystal Structure Database (ICSD). Within these structures, S8 molecules assume a parallel-displaced alignment. Quantum chemical calculations confirm that the parallel-displaced orientation represents the most stable geometry for two S8 molecules. The interaction energy for the most stable geometry is calculated to be ∆ECCSD(T)/CBS= -8.70 kcal/mol. According to the energy decomposition analysis performed using the SAPT 2+(3) method, the dominant attractive force between two S8 molecules arises from dispersion interactions with the significant contribution of electrostatics.