Thermal, dielectric and vibrational properties of allylammonium chloroantimonates(III) and chlorobismuthates(III): [C3H5NH3]3[BiCl6] and [C3H5NH3]3[SbCl5]Cl

The allylammonium hexachlorobismuthate(III), [C3H5NH3]3[BiCl6], and the allylammonium pentachloroantimonate(III), [C3H5NH3]3[SbCl5]Cl, compounds have been synthesized and studied by means of differential scanning calorimetry, thermal expansion, dielectric and infrared (IR) techniques. [C3H5NH3]3[BiCl6] exhibits three solid–solid structural phase transitions (PTs) at: 304/304 K (I ↔ II) (upon cooling/heating), 195/197 K (II ↔ III) and 155/156 K (III ↔ IV). In turn [C3H5NH3]3[SbCl5]Cl exhibits two PTs at: 221/221 K (I ↔ II) and 181/185 K (II ↔ III). The dielectric studies have been made in the frequency range of 2 kHz–1 MHz between 100 and 350 K. The dielectric relaxation processes are observed in both crystals. The activation energy (EA) value of the dielectric relaxation process for [C3H5NH3]3[BiCl6] amounts to about 43 and 72 kJ mol−1 for the low- and high-temperature relaxation, respectively, whereas for [C3H5NH3]3[SbCl5]Cl EA = 15 kJ mol−1. The infrared spectra of [C3H5NH3]3[BiCl6] and [C3H5NH3]3[SbCl5]Cl have been recorded over the wavenumber range between 3800 and 40 cm−1 at selected temperatures (10–310 K). The mechanisms of PTs in the title compounds are discussed.

► We examine two compounds: [C3H5NH3]3BiCl6 and [C3H5NH3]3SbCl5Cl.
► Crystals undergo PTs characterized by thermal, dielectric and infrared methods.
► Infrared studies confirmed a contribution of the organic cations to the PT mechanism.