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首页> 外文期刊>Chemistry: A European journal >Giant deuteron migration during the isosymmetric phase transition in deuterated 3,5-pyridinedicarboxylic acid
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Giant deuteron migration during the isosymmetric phase transition in deuterated 3,5-pyridinedicarboxylic acid

机译：氘代3,5-吡啶二羧酸等对称相变过程中的巨大氘核迁移

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摘要

Deuterated 3,5-pyridinedicarboxylic acid exhibits reversible temperature-induced deuteron migration of a magnitude unprecedented in this class of compounds. We used a combination of variable-temperature powder and single-crystal neutron diffraction and density functional theory (DFT)-based computational methods to elucidate the origin of this remarkable behaviour. Single-crystal neutron diffraction shows that between 15 and 300 K, the deuteron moves by 0.32(1) ? and the structure changes from a low-temperature N-D?O form to a high-temperature N?D-O form. Variable-temperature powder neutron-diffraction data, which was fitted by using parametric Rietveld refinement, show that this deuteron migration is due to an isosymmetric, first-order phase transition that occurs by growth of the daughter phase in the parent-phase matrix. Similar phase transitions are observed in two selectively deuterated forms of the material. DFT calculations demonstrate the role of phonons and show that vibrational free-energy stabilisation, which plays a key role in the observed structural phase transitions, is more pronounced in the fully deuterated material and proportional to the mass of the molecule, that is, the level of deuteration. This is consistent with our experimental work, for which distinct crystallographic phase transitions were clearly observed for the three deuterated systems, but not for the fully protonated material.
机译：氘代的3,5-吡啶二甲酸显示出可逆的温度诱导的氘代迁移，其幅度在此类化合物中是前所未有的。我们结合了变温粉末和单晶中子衍射以及基于密度泛函理论（DFT）的计算方法，来阐明这种现象的起源。单晶中子衍射表明，氘核在15和300 K之间移动0.32（1）？其结构从低温的N-D 2 O形式转变为高温的N-D-O形式。通过使用参数Rietveld精修拟合得到的变温粉末中子衍射数据表明，氘核迁移是由于在母相矩阵中子相的生长引起的等对称的一阶相变。在材料的两种选择性氘代形式中观察到相似的相变。 DFT计算证明了声子的作用，并且表明在观察到的结构相变中起关键作用的振动自由能稳定化在完全氘化的物质中更加明显，并且与分子的质量成正比，即氘。这与我们的实验工作是一致的，对于这三个氘代系统，可以清楚地观察到明显的结晶相变，而对于完全质子化的材料则不能观察到。

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