Tris(allylammonium) Hexabromobismuthate(III) – Crystal Structure, Phase Transitions and Thermal, Dielectric, Vibrational and ¹H NMR Properties Over a Range of Temperatures

Abstract

A novel inorganic‐organic hybrid compound, allylammonium hexabromobismuthate(III), (C3H5NH3)3BiBr6 (ABB), was synthesised and its structure determined by means of single‐crystal X‐ray diffraction studies at four temperatures (280, 230, 170 and 100 K). At 100 K, the compound crystallises in the monoclinic space group, C2/c. Its crystal structure consists of discrete BiBr63– anions and three inequivalent allylammonium (C3H5NH3)+ cations. Four solid‐solid structural phase transitions for ABB were detectable by means of DSC and dilatometric techniques: continuous (I↔II) at 272/272 K (upon heating/cooling), discontinuous (II↔III) at 218/215, discontinuous (III↔IV) at 205/204 K and discontinuous (IV↔V) at 146/144 K. The ferroelastic domain structure was observed over one intermediate phase (III) below 215 K. The electric properties of ABB have been measured over a wide temperature range (105–310 K). Low frequency relaxation processes with dielectric increments Δϵ1 ≈ 0.9 and Δϵ2 ≈ 0.05 were observed within phases II and V, respectively. Temperature‐dependent vibrational properties of ABB in the frequency region 3500–500 cm–1 and the molecular motions of its allylammonium cations were studied by means of proton magnetic resonance. The mechanisms of the phase transitions in the title compound are discussed.

An Above‐Room‐Temperature Phase Transition with Dielectric‐Switching Properties in a Halogenobismuthate(III) – Tris(Cyclohexylmethylammonium) Pentabromobismuthate(III) Bromide

“…Thus, it is of great significance to design and construct new functional solid‐state phase‐transition compounds . Though various strategies have been developed to construct solid‐state phase‐transition materials, the prediction and design of new high‐performance phase‐transition materials remains challenging owing to their complicated molecular interactions . Recent progress in research into solid‐state phase transitions, associated with the reorientational motion of the flexible cations in organic–inorganic hybrids, has offered a potentially effective strategy for the exploration of new phase‐transition materials .…”

Phase transitions in (C7H12N2)2[SnCl6]Cl2·1.5H2O crystal, studied by NMR and infrared spectroscopy

“…However, above the second temperature phase transition (Tc 2 = 393 K), the simulation of these spectra shows that a splits of all chemical shifts represent the organic C 7 H 12 N 2 group. These splitting that was observed by 13 C deconvolution spectra in Phases II and III indicated that those phases are ferroelastic …”

Order-Disorder Phase Transition, Anisotropic and Switchable Dielectric Constants Induced by Freeze of the Wheel-Like Motion in a Hexafluorosilicate-Based Crystal

“…During the phase transition, molecular motions are frozen on cooling and cause a decrease in ϵ′. Therefore, temperature‐dependent ϵ′ would provide relevant information on dynamics of phase transitions . Here, variable‐temperature dielectric spectroscopy of single crystals of 1 was measured at a frequency of 100 KHz (Figure ).…”