Dibutylammonium Hydrogen Oxalate: An Above-Room-Temperature Order–Disorder Phase Transition Molecular Material

An above-room-temperature new phase transition molecular material, dibutylammonium hydrogen oxalate (1), has been synthesized, which undergoes a reversible phase transition at 321.6 K. Differential scanning calorimetry (DSC) measurements confirm its reversible phase transition with a large heat hysteresis of ∼10 K. The dielectric constants of 1 exhibit an obvious step-like anomaly, showing the high and low dielectric constant states at high and room-temperature phases, respectively, which reveal that 1 might be considered a potential switchable dielectric material. Variable-temperature single crystal X-ray diffraction analyses disclose that the origin of this phase transition is greatly attributed to the coupling of the order–disorder change and reorientation of the dibutylammonium cation; that is, the frozen ordering of ethyl group in butyl moiety triggered by the decreasing temperature forces the reorientation of cation, thus resulting in the structural phase transition.