Crystal supramolecularity: an unusual occurrence of benzene trapped in edge-to-edge conformation

Abstract

The crystal supramolecularity of the compound [(Ph₃PAu)₄S]²⁺ (ClO₄^?)₂ (C₆H₆)₂ (CH₂Cl₂)₂ reported by Canales et al. (F. Canales, M. C. Gimeno, A. Laguna and M. D. Villacampa, Inorg. Chim. Acta, 1996, 244, 95) has been analysed and found to be based on sixfold phenyl embraces involving all Ph₃P ligands, generating two-dimensional nets of cations, which are corrugated by the geometry of the cation imposed by the pyramidal S atom. The stacking of these corrugated layers generates cavities which contain almost planar quartets of benzene molecules. These benzene molecules are constrained to an uncommon and less attractive edge-to-edge geometry, which is compensated by the favourable edge-to-face interactions between the phenyl rings of the Ph₃P ligands and the included benzene molecules. The calculated intermolecular energy for a pair of benzene molecules in this edge-to-edge geometry is < 0.1 kcal mol^?1.