Two novel metal–organic coordination polymers based on ligand 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide with phase transition, and ferroelectric and dielectric properties

Abstract

Two novel metal–organic complexes {[Ag₃(dabcodo)(NO₃)₃]·H₂O}_n (1) and [Ca(dabcodo)(H₂O)₄Cl₂]_n (2) containing metal salt and 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide (dabcodo), in which dabcodo is coordinated with two types of metal ions, were successfully synthesized. Differential scanning calorimetry, powder X-ray diffraction, variable-temperature structural analyses, dielectric measurements and rectangular polarization-electric field hysteresis loops revealed that 1 underwent phase transition from room-temperature-phase Pca2₁ to low-temperature-phase Cc at T_t ≈ 217 K, accompanied by remarkable dielectric relaxation. Compound 1 was a typical ferroelectric–ferroelectric phase transition material with an electric hysteresis loop showing a remnant polarization (P_r) of ca. 0.23 μC cm⁻² and a coercive field (E_c) of 6.5 kV cm⁻¹. Room-temperature and low-temperature phases of 1 featured the same topology structure of {3⁴·4⁶·5¹⁷·6¹⁶·7²}. Compound 2 underwent a paraelectric–paraelectric phase transition from room-temperature-phase I4/mmm to low-temperature-phase Cmcm at T_t ≈ 177 K. Moreover, this study contributes to a deeper understanding of the structure–property relationship in emerging metal–organic ferroelectrics.