Modulating molecular structures and dielectric transitions in organic–inorganic hybrid crystals

Abstract

In this paper, three new hybrid phase transition compounds, [Hmpy]CdBr₃ (1, Hmpy = N-methylpyrrolidinuium cation), [Hmpy]₂CdBr₄ (2) and [Hmpy]₃CdBr₃·CdBr₄ (3), were synthetized by means of regulating the ratio of reactants. Systematic characterizations consisting of variable temperature X-ray single crystal diffraction, differential scanning calorimetry (DSC) and dielectric measurements reveal that 1 with infinite one-dimensional (1D) [CdBr₃]_n⁻ chains undergoes a phase transition around 278 K; 2 with isolated [CdBr₄]²⁻ tetrahedrons exhibits a high-temperature phase transition close to 367 K, accompanied by prominent switchable dielectric behavior. Interestingly, 1D [CdBr₃]_n⁻ chains and isolated [CdBr₄]²⁻ tetrahedrons both exist in 3, associated with a phase transition at 320 K. The phase transitions in the three compounds are originated from the order-disorder transitions of the Hmpy cation. It is expected that our finding would promote the development of hybrid dielectric transition materials with adjustable properties.