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

• Published in: Journal of molecular structure 2012-11, Vol.1028, p.79-87
• Main Authors: Ouasri, A., Jeghnou, H., Rhandour, A., Mazzah, A., Roussel, P.
• Format: Article
• Language: English
• Subjects: Beta; Cations; Chemical Sciences; Crystals; Differential scanning calorimetry; DSC; Hexylenediammonium; Inorganic chemistry; Molecular structure; Order disorder; Pentachlorobismuthate (III); Phase transformations; Thermodiffractogramme; X-ray diffraction; X-rays
• ISSN: 0022-2860; 1872-8014; 0022-2860
• DOI: 10.1016/j.molstruc.2012.05.061

► X-ray analysis: the crystal shows 2 phase transitions: α (223K) ↔ β (308K) ↔γ (373K). ► A paraelastic-ferroelastic transition may be occurred between γ and β phases. ► DSC analysis: α ↔ β and β ↔ γ are of first-order and weak first-order type, respectively. ► Raman spectra: anionic and cationic motions contribute to phase transition mechanisms. ► Order-disorder type of α ↔ γ transition is due to changes in dynamical state of cations. [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 286K and 326K as it was indicated by crystallography analysis: α(P212121, Z=4 at 223K)↔β(P21/n, Z=8 at 308K)↔γ(Pnma, Z=4 at 373K). The DSC analysis (on heating and cooling) confirm the existence of these phase transitions at 291/286K and 326/325K 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 (BiCl52-)n units composed of distorted BiCl63-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 +NH3(CH2)6NH3+ cations which are performing some kind of reorientational or rotational motions above 298K.