Phase transitions and distortion of [BiCl6]3- octahedra in (C3H5NH3)3[BiCl6] -: DSC and single-crystal X-ray diffraction studies

The DSC diagram of tris(allylammonium) hexachlorobismuthate(III), (C3H5NH3)(3)[BiCl6], revealed three anomalies at 152, 191 and 299 K. The structure of the salt was determined at 200 and 315 K, below and above the high-temperature phase transition at 299 K. In both phases the crystals are monoclinic. At 200 K the space group is C2/c whereas at 315 K it is C2/m. The structures, at both temperatures, are composed of [BiCl6](3-) octahedra and allylammonium cations. The organic and inorganic moieties are attracted to each other by a network of the N-(HCl)-Cl-... hydrogen bonds. The relationship between corresponding parameters of the unit cells has been found. The phase transition at 299 K, of the order-disorder type, is attributed to the ordering of one non-equivalent allylammonium cation in the low-temperature phase.