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.