Structural Diversity and Stability of Organic–Inorganic Hybrid Quinuclidine-Based Metal Bromides

Organic–inorganic hybrid compounds based on quinuclidinium and metal bromides, (C₇H₁₄N)₂MBr₄ (M = Co, Mn, Cd), have been synthesized. Differential scanning calorimetry measurements indicate that all compounds undergo a reversible phase transition at 251 K (Co), 205 K (Mn), and 363 K (Cd) upon heating. The respective temperature dependences of the dielectric permittivity reveal anomalies, confirming the occurrence of phase transitions. Although the crystals are isostructural at room temperature, as confirmed by X-ray diffraction data, the mechanism of the phase transitions varies in each compound. The main driving force is the reorientation of quinuclidinium, resulting in the rearrangement of hydrogen bonds. Satisfactory dielectric and thermal stability properties of these materials have been demonstrated, highlighting their potential for applications in temperature sensors and switch devices.