2 H NMR study of phase transition and hydrogen dynamics in hydrogen bonded organic antiferroelectric 55DMBP-H 2 ca
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2H
NMR study of phase transition and hydrogen dynamics in hydrogen bonded organic antiferroelectric 55DMBP-H2 ca
Tetsuo Asaji1,2 · Masamichi Hara1 · Hiroki Fujimori1,2 · Shoko Hagiwara2
© Springer International Publishing Switzerland 2016
Abstract Hydrogen dynamics in one-dimensional hydrogen bonded organic antiferroelectric, co-crystal of 5,5’-dimethyl-2,2’-bipyridine (55DMBP) and chloranilic acid (H2 ca), was investigated by use of 2 H high resolution solid-state NMR. The two types of hydrogen bonds O-H. . .N and N+ -H. . .O− in the antiferroelectric phase were clearly observed as the splitting of the side band of the 2 H MAS NMR spectra of the acid-proton deuterated compound 55DMBP-D2 ca. The temperature dependence of the spin-lattice relaxation time was measured of the N+ -H and O-H deuterons, respectively. It was suggested that the motion of the O-H deuteron is already in the antiferroelectric phase in the fast-motion regime in the NMR time scale, while that of the N+ -H deuteron is a slow motion. In the high-temperature paraelectric phase, the both deuterons become equivalent and the fast motion of the deuterons in the NMR time scale is taking place with the activation energy of 7.9 kJ mol−1 . Keywords Organic compounds · Nuclear magnetic resonance(NMR) · Phase transition · Ferroelectricity
1 Introduction Recently, there are significant advances in molecular ferroelectrics [1, 2]. The organic materials based on non-covalent molecules formed by two or more components were shown to This article is part of the Topical Collection on Proceedings of the International Conference on Hyperfine Interactions and their Applications (HYPERFINE 2016), Leuven, Belgium, 3-8 July 2016 Tetsuo Asaji
[email protected] 1
Department of Chemistry, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan
2
Department of Chemistry, Graduate School of Integrated Basic Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550, Japan
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Fig. 1 One-dimensional hydrogen-bond of organic antiferroelectric 55DMBP-H2 ca in paraelectric (above) and antiferroelectric (below) phases
have high ability to realize room temperature ferroelectrics with large spontaneous polarization as well as easier polarization switching [1]. Hydrogen bonding plays an important role in these new types of organic ferroelectrics. Supramolecular structure, which may be crucial for them, is constructed by co-crystallization of different molecules by intermolecular hydrogen bonds. Therefore, it is definitely very important to understand deeply the hydrogen bonds in these co-crystals. 5,5’-dimethyl-2,2’-bipyridine (55DMBP) and chloranilic acid (H2 ca) forms a hydrogenbonded supramolecular compound 55DMBP-H2 ca, in which the two types of molecules are alternately connected by (O, O− ). . .H+ . . .N and N. . .H+ . . .(O− , O) bifurcated hydrogen bonds as shown in Fig. 1 at higher temperature [3]. Below Tc = 318 K, proton transfer tak
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