Intermolecular correlations of racemic mixtures – comparison between liquid S₂Cl₂ and Se₂Br₂

ABSTRACT

Liquid chalcogen-halogen A₂X₂ (A: S, Se, X: Cl, Br) is a racemic mixture of enantiomers between left-handed (L) and right-handed (D) chiral molecules. The lone-pair orbital of the chalcogen atom significantly affects the molecular conformation and intermolecular interaction. The latter depends on the size of the orbital and number density. High-energy X-ray diffraction measurements and reverse Monte Carlo (RMC) structural modelling were performed for liquid S₂Cl₂ in addition to the previous structural analysis for liquid Se₂Br₂. By comparing the structures of the RMC model and hard-sphere Monte Carlo (HSMC) model, the effect of refinement on the experimental structure factor can be analysed. In this paper, nearest-neighbour intermolecular pairs are classified in terms of enantiomer pairs such as like-pair (L-L and D-D) and unlike-pair (L-D). As a result, the effect of a strong intermolecular attractive interaction is detected in Se₂Br₂ as increasing the number of like-pairs with geometrical advantages from HSMC to RMC, whereas that of an intermolecular repulsive interaction is observed in S₂Cl₂ as elongation of the averaged intermolecular S-S distance from HSMC to RMC. These results are consistent with the results of the ab initio molecular dynamics simulation for Se₂Cl₂ and S₂Cl₂.

KEYWORDS:

• Molecular liquid
• reverse Monte Carlo
• structure
• sulfur chloride
• selenium bromide

Acknowledgements

High-energy X-ray diffraction measurements were performed at the BL04B2 beamline at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2004B0629 and 2010A1541).

Disclosure statement

No potential conflict of interest was reported by the author.