X-ray, thermal and vibrational studies of two structural phases transition in hexylenediammonium pentachlorobismuthate (III) [NH3(CH2)6NH3]BiCl5

[NH3(CH2)6NH3]BiCl5 crystal has been studied by means of X-ray diffraction, DSC and vibrational spectroscopy techniques. The X-ray powder study showed that the crystal exhibits two phase transitions near 286 K and 326 K as it was indicated by crystallography analysis: α(P212121, Z = 4 at 223 K) ↔ β(P21/n, Z = 8 at 308 K) ↔ γ(Pnma, Z = 4 at 373 K). The DSC analysis (on heating and cooling) confirm the existence of these phase transitions at 291/286 K and 326/325 K and indicate that α ↔ β phase transition is of first-order character, but β ↔ γ one is of weak first-order type. Infrared and Raman spectra which interpreted at room temperature indicated that the [NH3(CH2)6NH3]BiCl5 structure was consisted of isolated ( BiCl 5 2 - ) n units composed of distorted BiCl 6 3 - octahedra. Raman spectroscopy at various temperatures showed that both anionic and cationic motions contribute to the complex transition mechanisms. The character order–disorder of β ↔ γ phase transition is undoubtedly related to the change in dynamical state of + NH 3 ( CH 2 ) 6 NH 3 + cations which are performing some kind of reorientational or rotational motions above 298 K.