Metal-free enantiomorphic perovskite [dabcoH][HO]Br and its one-dimensional polar polymorph.

The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH]HOBr (where [dabcoH] = 1,4-di-aza-bicyclo-[2.2.2]octane dication) correspond to the general formula characteristic of perovskites. In enantiomorphic trigonal polymorph α of [dabcoH]HOBr , the corner-sharing [HO]Br octahedra combine into a 3D framework embedding [dabcoH] dications in pseudo-cubic cages. In the more dense polymorph β, the face-sharing [HO]Br octahedra form 1D polyanionic columns separated by [dabcoH] dications. These different topologies correlate with different crystal fields around the cations and their different disorder types: orientational disorders of [dabcoH] dications and HO cations in polymorph α and positional disorder of [HO] cations in polymorph β. The orientational disorder increases the lengths of OH⋯Br hydrogen bonds in polymorph α, but NH⋯Br distances of ordered dabcoH dications are longer in polymorph β. The presence of polar [HO] cations in [dabcoH]HOBr polymorphs offers additional polarizability of the centres compared with analogous metal-free [dabcoH][NH]Br perovskite.