High-Temperature and Pressure-Induced Ferroelectricity in Hydrogen-Bonded Supramolecular Crystals of Anilic Acids and 2,3-Di(2-pyridinyl)pyrazine
详细信息 查看全文
- 作者：Sachio Horiuchi ; Reiji Kumai ; Yoshinori Tokura
- 刊名：The Journal of the American Chemical Society
- 出版年：2013
- 出版时间：March 20, 2013
- 年：2013
- 卷：135
- 期：11
- 页码：4492-4500
- 全文大小：548K
- 年卷期：v.135,no.11(March 20, 2013)
- ISSN：1520-5126
文摘
Cocrystallization of anilic acids (H2xa) and 2,3-di(2-pyridinyl)pyrazine (dppz) affords a variety of molecular geometries, including hydrogen-bonding and supramolecular structures. Proton-transferred 1:1 salts of [H-dppz][Hca] and [H-dppz][Hba] (H2ca = chloranilic acid, H2ba = bromanilic acid) were found to host room-temperature ferroelectricity with a spontaneous polarization of 3鈥? 渭C/cm2 along the hydrogen-bonded chains. Compared with the Curie points of other supramolecular ferroelectrics, those of the salts are relatively high (402 K and >420 K, respectively) because of the elongated hydrogen bonds, which stabilize the proton-ordered state against thermal agitation. In addition to the ferroelectric black (伪) form, dppz and H2ba gave two different crystal forms with a 2:3 ratio: the brown 尾 form of [H1.5-dppz]2[Hba]3 and the brownish-red 纬 form of [H-dppz]2[Hba]2[H2ba]. Mixed solutions of dppz with the less acidic fluoranilic acid (H2fa) exhibit valence instability; the H2fa molecules remain mostly neutral in absolute ethanol, whereas methanol (MeOH) solution apparently increases the deprotonated Hfa鈥?/sup> content. Crystallizations of these solutions gave a neutral [dppz][H2fa] cocrystal and ionic [H-dppz+][Hfa鈥?/sup>]路MeOH salt, respectively. The ferroelectricity induced by a modest hydrostatic pressure corroborates the conclusion that the ionic state with a dipolar [H-dppz+][Hfa鈥?/sup>] chain is energetically close to the nonpolar neutral ground state of the [dppz][H2fa] crystal.