Switchable Dielectric Materials Based on a Diprotonated Organic Cation Containing Two Different Anions: (C5H16N2)BF4X (X = Cl, Br, NO3)

Three molecular-based phase transition compounds, namely, (C5H16N2)BF4Cl (1, C5H16N2 = diprotonated 2,2-dimethyl-1,3-propanediamine), (C5H16N2)BF4Br (2), and (C5H16N2)BF4NO3 (3), were synthesized and characterized. Differential scanning calorimetry and the step-like anomaly of the real part (6 ') of the temperature-dependent dielectric constant revealed that the compounds underwent reversible first-order phase transition with high phase transition temperature under the stimulation of temperature. Variable-temperature X-ray diffraction analysis revealed that the microcosmic driving force of phase transition was the order-disordered change of the organic cation and spherical anion. Notably, the diprotonated organic cations were charge-balanced by two different anions of the combination BF4- and Cl-, Br- and NO3-. Our research paves a new avenue to construct molecular-based phase transition materials with temperature stimulus response.