A novel framework of N-H...Br hydrogen bonds forming Br(4,4'-bipyridinium)(4) supramolecular synthons: bis(4,4'-bipyridinium) tris[tetrabromidoferrate(III)] bromide.

In the asymmetric unit of the title compound, (C(10)H(10)N(2))(2)[FeBr(4)](3)Br, the Fe atoms are in a distorted tetrahedral environment. The crystal structure contains a novel arrangement of Br(4,4'-bipyridinium)(4) supramolecular synthons assembled via short N-H...Br hydrogen bonds (H...Br = 2.55, 2.40, 2.38 and 2.55 A), where four cations surround one nonbonded bromide ion in a tetrahedral arrangement. These synthons are further connected by hydrogen bonds using the remaining terminal NH hydrogens in each cation and the Br(-) ions to form an adamantoid-like network and thus produce a three-dimensional supramolecular architecture with the [FeBr(4)](-) ions located in the cavities. The structure shows no significant intermolecular Br...Br, Br...aryl or aryl-aryl interactions.