Crystal structure, phase transitions and Raman scattering in the new non‐centrosymmetric [(C3H7)4N]3Bi3Br12 compound

Abstract

AbstractA novel tri‐tetrapropylammonium dodeca bromobismuthate (III) compound has been synthesized and studied by single‐crystal X‐ray diffraction, differential scanning calorimetry, and Raman spectroscopy as a function of temperature. At room temperature, the title compound crystalizes in noncentrosymmetric Cc space group which belongs to monoclinic crystal system. The unit cell dimensions are a = 11.083(6) Å, b = 19.100(6) Å, c = 31.146(3) Å, β = 98.42(0)°, and V = 6522.69(9) Å3. The crystal package is provided by electrostatic interactions and hydrogen bonds (C–H … Br). Intermolecular interactions present in the grown single crystal were analyzed by Hirshfeld surface and 2D fingerprint plot. The differential scanning calorimetry reveals two reversible phase transitions at 297 and 430 K. The values of the transition entropies suggest that the first is of an order–disorder type, while the second appears as a displacive one. The Raman versus temperature studies show that the vibrational states of tetrapropylammonium cations change markedly through the phase transitions. The most important changes are observed for two lines at 1034 and 1449 cm−1 (at room temperature) issued from the νs(N–C–C) + δs(C–N–C) and δs (CH3) of the cations. The spectral characteristics of these lines are analyzed and consistently described in the framework of an order–disorder model for the phase transitions.