The preparation and properties of the new hexabromodiquinoline derivative 4 are described. This lattice inclusion host shows a strong preference for trapping small aromatic hydrocarbons. The X-ray crystal structures of the benzene, toluene, o-xylene, and p-xylene compounds are reported, and are analysed from a crystal engineering perspective. Crystallisation of 4 from the dual-nature solvent trifluoromethylbenzene yields the solvent-free material. Comparison of the parent crystal structure with those of its inclusion compounds reveals why inclusion of aromatic hydrocarbon guests is such a favoured process. The high concentration of Br⋯Br interactions in the structure of pure 4 is diluted and increasingly replaced by aromatic offset face–face (OFF) and aromatic edge–face (EF) interactions in the inclusion compounds, and this results in better lattice packing energies. For toluene, o-xylene, and p-xylene the host–guest ratio is 1 ∶ 1. Inclusion of the smaller benzene molecule results in a change to 2 ∶ 3 stoichiometry. This increase in guest content is assisted by replacement of host–host OFF and EF motifs with host–host pi-halogen dimer (PHD) interactions, which provide space for inclusion of the additional guest molecules. These changes result in the most efficient lattice packing of the series for compound (4)2·(benzene)3.
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