Temperature study of [N(C3H7)4]2Cd2Cl6 by thermal analysis, Raman scattering, and X-ray powder diffraction: Evidence of phase transitions

The phase transitions of [N(C3H7)(4)](2)Cd2Cl6 have been evidenced by differential scanning calorimetry (DSC), and the different phases have been studied by Raman scattering on single crystals, in the frequency range 50-3900 cm(-1) for temperatures ranging between 294 and 451 K. On heating, two reversible phase transitions are observed at T-1 = 321.5 K (weakly first order, with 1.2 K hysteresis) and T-2 = 323.6 K (second order), and a strongly first-order transition occurs in the vicinity of 448 K (T-3), with breaking of the crystal and decrease of the temperature of transition for successive temperature cycles. The temperature dependence of the Raman line shifts nu, the half-width Delta nu, and the relative intensities show weak singularities in the vicinity of T-1 and T-2 and marked effects on approaching T-3. The X-ray powder diffraction patterns at room temperature prior to and after the T-3 phase transition show that it is irreversible, although the diffractograms look qualitatively very similar. (C) 2011 Elsevier B.V. All rights reserved.