Phase transitions and electric properties of imidazolium chlorobismuthate(III): [C3H5N2]6[Bi4Cl18]

[C3H5N2]6[Bi4Cl18] crystallizes at room temperature in the monoclinic space group; C2/m. It undergoes two solid–solid phase transitions of first-order type at 221/218 K (heating–cooling) from phase I to II and at 195/145 K from phase II to III. The dielectric relaxation process was found to appear in a kilohertz frequency region over the phase III with the activation energy c.a. 14 kJ/mol. A polydispersive character of the dielectric dispersion indicates a presence of complex molecular motions of dipolar groups in the crystal. The mechanism of the phase transitions in [C3H5N2]6[Bi4Cl18] is proposed.