A ^<14>N nuclear quadrupole resonance study of phase transitions and molecular dynamics in hydrogen bonded organic antiferroelectrics 55DMBP-H_2ca and 1,5-NPD-H_2ca
A ^<14>N nuclear quadrupole resonance study of phase transitions and molecular dynamics in hydrogen bonded organic antiferroelectrics 55DMBP-H_2ca and 1,5-NPD-H_2ca
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氢键有机反铁电体55DMBP-H_2ca和1,5-NPD-H_2ca相变和分子动力学的^<14>N核四极共振研究
DOI：
10.1039/c0cp02873h
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Hiroyuki Ishida
中科院分区：
文献类型：
--
作者：
Janez Seliger;Veselko Zagar;Tetsuo Asaji;Kazuma Gotoh;Hiroyuki Ishida
测量了反铁电顺电55 DMBP-H_2ca和1，5-NPD-H_2ca中~（14）N核四极共振频率的温度依赖性。在这两种化合物中，我们观察到反铁电相中的两个不等价的氮位置（N+-H <$O−和N <$H-O）。在顺电相中，两个氮的位置变得相等（N <$H <$O）。由NQR数据确定了局域反铁电序参量的临界指数。四极耦合张量的主值在这两种化合物中相关。相关图清楚地显示了质子如何在温度升高时从反铁电位置向分叉氢键中的顺电位置迁移。通过~ 1H和~（14）N自旋-晶格弛豫，观察到~（55）DMBP-H_2ca的慢运动.自旋晶格弛豫数据的分析表明，两个非平面构象的联吡啶分子之间的缓慢交换。
The temperature dependence of the 14N NQR frequencies has been measured in antiferroelectric and paraelectric 55DMBP–H2ca and 1,5-NPD–H2ca. In both compounds we observe two non-equivalent nitrogen positions (N+–H⋯O− and N⋯H–O) in the antiferroelectric phase. The two nitrogen positions become equivalent (N⋯H⋯O) in the paraelectric phase. The critical exponent of the local antiferroelectric order parameter has been determined from the NQR data. The principal values of the quadrupole coupling tensor correlate in both compounds. The correlation diagrams clearly show how a proton migrates from the antiferroelectric position towards the paraelectric position in the bifurcated hydrogen bond on increasing the temperature. A slow motion has been observed in 55DMBP–H2ca by the 1H and 14N spin–lattice relaxation. An analysis of the spin–lattice relaxation data suggests a slow exchange between two non-planar conformations of the bipyridine molecule.