Crystal structure and phase transitions in dipropylammonium hexachloroantimonate(V): [N(C3H7)2H2][SbCl6]

The crystal structure of dipropylammonium hexachloroantimonate(V), [N(C3H7)2H2][SbCl6] (DPACA) has been determined by means of X-ray diffraction at 290 K. The compound crystallizes in the monoclinic space group: P21/n. The crystal undergoes three structural phase transitions: two first-order type at 388/376 K (heating-cooling) from phase (I) to (II) and at 157/144 K from phase (III) to (IV), and one second-order type at 210 K from phase (II) to (III). The dielectric relaxation process has been found to appear in a kilohertz frequency region over the phases (II) and (III) with the activation energy ca. 28 kJ mol−1. 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 DPACA is proposed.