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

[NH3(CH2)(6)NH3]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: alpha(P2(1)2(1)2(1), Z = 4 at 223 K) <-> beta(P2(1)/n, Z = 8 at 308 K) <-> gamma(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 alpha <-> beta phase transition is of first-order character, but beta <-> gamma one is of weak first-order type. Infrared and Raman spectra which interpreted at room temperature indicated that the [NH3(CH2)(6)NH3]BiCl5 structure was consisted of isolated (BiCl52-)(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 beta <-> gamma phase transition is undoubtedly related to the change in dynamical state of +NH3(CH2)(6)NH3+ cations which are performing some kind of reorientational or rotational motions above 298 K. (C) 2012 Elsevier B.V. All rights reserved.