Metal-free enantiomorphic perovskite [dabcoH 2 ] 2+ [H 3 O] + Br - 3 and its one-dimensional polar polymorph.

The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH 2 ] 2+ H 3 O + Br - 3 (where [dabcoH 2 ] 2+ = 1,4-di-aza-bicyclo-[2.2.2]octane dication) correspond to the general formula ABX 3 characteristic of perovskites. In enantiomorphic trigonal polymorph α of [dabcoH 2 ] 2+ H 3 O + Br - 3 , the corner-sharing [H 3 O]Br 6 octahedra combine into a 3D framework embedding [dabcoH 2 ] 2+ dications in pseudo-cubic cages. In the more dense polymorph β, the face-sharing [H 3 O]Br 6 octahedra form 1D polyanionic columns separated by [dabcoH 2 ] 2+ dications. These different topologies correlate with different crystal fields around the cations and their different disorder types: orientational disorders of [dabcoH 2 ] 2+ dications and H 3 O + cations in polymorph α and positional disorder of [H 3 O] + 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 2 dications are longer in polymorph β. The presence of polar [H 3 O] + cations in [dabcoH 2 ] 2+ H 3 O + Br - 3 polymorphs offers additional polarizability of the centres compared with analogous metal-free [dabcoH 2 ] 2+ [NH 4 ] + Br - 3 perovskite.