Ordered Matter Science Research Center, Southeast University, Nanjing 211189, P. R. China.
J Am Chem Soc. 2012 Jul 4;134(26):11044-9. doi: 10.1021/ja3047427. Epub 2012 Jun 21.
A novel mononuclear metal-organic compound, [Cu(Hdabco)(H(2)O)Cl(3)] (1, dabco = 1,4-diazabicyclo[2.2.2]octane) in which the Cu(II) cation adopts a slightly distorted bipyramidal geometry where the three Cl anions constitute the equatorial plane and the Hdabco cation and H(2)O molecule occupy the two axial positions, was synthesized. Its paraelectric-to-ferroelectric phase transition at 235 K (T(c)) and dynamic behaviors were characterized by single crystal X-ray diffraction analysis, thermal analysis, dielectric and ferroelectric measurements, second harmonic generation experiments, and solid-state nuclear magnetic resonance measurements. Compound 1 behaves as a molecular rotor above room temperature in which the (Hdabco) part rotates around the N···N axis as a rotator and the [Cu(H(2)O)Cl(3)] part acts as a stator. In the temperature range 235-301 K, a twisting motion of the rotator is confirmed. Below the T(c), the motions of the rotor are frozen and the molecules become ordered, corresponding to a ferroelectric phase. Origin of the ferroelectricity was ascribed to relative movements of the anions and cations from the equilibrium position, which is induced by the order-disorder transformation of the twisting motion of the molecule between the ferroelectric and paraelectric phases. Study of the deuterated analogue [Cu(Ddabco)(D(2)O)Cl(3)] (2) excludes the possibility of proton ordering as the origin of the ferroelectricity in 1.
一种新型单核金属-有机化合物，[Cu(Hdabco)(H(2)O)Cl(3)]（1，dabco=1,4-二氮杂二环[2.2.2]辛烷），其中 Cu(II)阳离子采用略微扭曲的双锥几何形状，其中三个 Cl 阴离子构成赤道平面，Hdabco 阳离子和 H(2)O 分子占据两个轴向位置，被合成。其顺电-铁电相转变在 235 K（T(c)）处，并通过单晶 X 射线衍射分析、热分析、介电和铁电测量、二次谐波产生实验和固态核磁共振测量来研究其动态行为。化合物 1 在室温以上表现为分子转子，其中（Hdabco）部分围绕 N···N 轴旋转作为转子，[Cu(H(2)O)Cl(3)]部分作为定子。在 235-301 K 的温度范围内，确认了转子的扭曲运动。在 T(c)以下，转子的运动被冻结，分子变得有序，对应于铁电相。铁电性的起源归因于阴离子和阳离子相对于平衡位置的相对运动，这是由分子在铁电相与顺电相之间的扭曲运动的无序-有序转变引起的。对氘代类似物[Cu(Ddabco)(D(2)O)Cl(3)]（2）的研究排除了质子有序作为 1 中铁电性起源的可能性。
