Ferroelectricity Induced by Ordering of Twisting Motion in a Molecular Rotor

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• 作者：Yi Zhang ; Wen Zhang ; Shen-Hui Li ; Qiong Ye ; Hong-Ling Cai ; Feng Deng ; Ren-Gen Xiong ; Songping D. Huang
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：July 4, 2012
• 年：2012
• 卷：134
• 期：26
• 页码：11044-11049
• 全文大小：411K
• 年卷期：v.134,no.26(July 4, 2012)
• ISSN：1520-5126

文摘

A novel mononuclear metal鈥搊rganic compound, [Cu(Hdabco)(H₂O)Cl₃] (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 H₂O 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路路路N axis as a rotator and the [Cu(H₂O)Cl₃] part acts as a stator. In the temperature range 235鈥?01 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鈥揹isorder transformation of the twisting motion of the molecule between the ferroelectric and paraelectric phases. Study of the deuterated analogue [Cu(Ddabco)(D₂O)Cl₃] (2) excludes the possibility of proton ordering as the origin of the ferroelectricity in 1.