Interplay between energy and geometry of parallel-displaced interactions in S8 dimer structures

Abstract

In this work we conducted a comprehensive study analyzing all crystal structures from the Cambridge Structural Database involving contacts between S8 molecules. Then, we combined those data with high-level quantum chemical calculations. The results revealed that the preferred orientation in the crystal structures is parallel-displaced. Quantum chemical calculations supported this finding, demonstrating that the most stable interaction in the S8 dimer occurs when two molecules adopt a parallel-displaced geometry resembling the one observed in the crystal structures. The interaction in the S8 dimer is very strong, with an energy of −8.70 kcal/mol, calculated at a highly accurate CCSD(T)/CBS level. In this stacking-like geometry, multiple S…S interactions can form, and the NCI analysis indicated an overlap of large surfaces of interacting molecules, significantly contributing to the system's stability. The SAPT2+(3) energy decomposition analysis showed that the predominant attractive force between two S8 molecules is dispersion, although the electrostatic component is also significant.