文摘
Ferroelectrics in metal鈥搊rganic materials have attracted recent interest owing to their synthetic simplicity and tunable nature. Utilizing isomeric dipodal phosphoramide ligands, L1 [PhPO(NH4Py)2] and L2 [PhPO(NH2Py)2], two new CuIIL2 derivatives, 1 ({[CuL12(H2O)2]路(NO3)2路(H2O)1.5路(CH3OH)}鈭?/sub>) and 2 ([CuL22]路(NO3)2), were synthesized. Compound 1 crystallizes in a noncentrosymmetric polar space group Cc as a two-dimensional framework, and 2 is a centrosymmetric complex. Electrical hysteresis (P鈥?i>E loop) measurements on 1 at room temperature gave the remnant (Pr) and saturation (Ps) polarization values of 27.96 and 21.79 渭C路cm鈥?, respectively, which are the highest among all of the known metal鈥搊rganic ferroelectric materials. Also, the Pr value obtained for 1 is comparable to that of barium titanate and higher than most of the organic, polymeric, and inorganic ferroelectric materials. The permittivity measurements on 1 and 2 result in high dielectric constant values of 186.3 and 53.24, respectively, at 1 Hz frequency at room temperature. Temperature-dependent permittivity measurement on 1 yields a dielectric anomaly peak at 40 掳C due to phase transition assisted by desolvation. The existence of phase transition is further confirmed by differential scanning calorimetry, powder X-ray diffraction, and polarized light microscopy. A comparison of the P鈥?i>E loops of 1, 1desolvated, and 1resolvated suggest that gasification/release of the solvate molecules from the packing structure affects the polarization in 1.