Switchable Dielectric Phase Transition Induced by Ordering of Twisting Motion in 1,4-Diazabicyclo[2.2.2]octane Chlorodifluoroacetate

A novel molecular electric ordered compound [(Hdabco)+ClF2CCOO–] (complex 1, dabco = 1,4-diazabicyclo[2.2.2]octane) has been discovered as a switchable dielectric material, in which the N–H···O hydrogen bonds connect the anions and cations together to form a dimer structure. It undergoes a reversible second order solid state phase transition at 165 K (Tc), which was confirmed by thermal analyses including differential scanning calorimetry (DSC) and specific heat (Cp) and dielectric measurements. Variable temperature single crystal X-ray diffraction analyses revealed its order–disorder transformation of twisting motion characteristic behaviors for the phase transition. Owing to the ordering of twisting motions of the chlorodifluoroacetate anions, the structure of 1demonstrates a phase transition from high crystallographic symmetry with space group of Pnmato the low state with space group of P21/c; that is, an Aizu notion of mmmF2/moccurs. Emphatically, the dielectric constant of 1displays a distinctive step-like anomaly; namely, it possesses a high dielectric state in the room temperature phase (RTP) and a low state in the low temperature phase (LTP). Such distinctive dielectric performances disclose that 1might be considered as a potential switchable dielectric material. We believe that all the findings would afford a useful strategy in exploring new electric ordering materials.