Two-point halogen bonding between 3,6-dihalopyromellitic diimides

The syntheses of 3,6-dichloro-, -dibromo-, and -diiodopyromellitic diimides - ACl, ABr, and AI, respectively - have been achieved. X-Ray crystallography of single crystals of ACl and ABr unveils the formation of extensive halogen-bonding networks in the solid state as a consequence of interactions between the lone pairs on the carbonyl oxygen atoms with the σ-holes of the halogen atoms. Further, the solid-state superstructure of diiodopyromellitic diimide is characterised by the formation of associated halogen-π dimers. The co-crystallisation of ACl or ABr with a 1,5-diaminonaphthalene derivative DN yields co-crystals of a mixed-stack charge-transfer (CT) complex which are supported by an expansive hydrogen-bonded network in addition to halogen-bonded belts that bring adjacent mixed-stacks into association with each other. 2,6-Dimethoxynaphthalene (DO) proved to be an effective CT complement to AI, yielding solvent-free co-crystals with superstructures which are comprised of a 1 - 2 ratio of AI to DO. This dimeric halogen-bonding motif is reminiscent of the formation of hydrogen-bonded dimers between carboxylic acids.