Mixed halobenzenes also prefer face⋯face approaches of aromatic rings, revealing a new inversion symthon

Abstract

Analysis of known crystal structures of halobenzenes reveals that the 176 closest intermolecular interactions contain either edge⋯face or face⋯face approaches between aromatic rings. Most of these close approaches possess the specific geometry and symmetry of π–π stacking defined as “symthon I”. A further 20 face⋯face approaches have similar geometry but exhibit only inversion symmetry, yielding a geometric definition for the new “symthon III”. There are 17 examples of edge⋯face approaches that meet the previously defined symmetry and geometric requirements for “symthon II”. The other close interactions are simple variants of these three symthons. Only symthon I accommodates halogen disorder and solid solutions – in this dataset exclusively in space group no. 14. The number (N) and disposition of halogen substituents influence the preferred symthons; for example edge⋯face interactions are confined to N ≤ 3. The inclusion here of halobenzenes containing more than one type of halogen completes an earlier study of unmixed halobenzenes.