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Polymorphism with Conformational Isomerism and Incomplete Crystallization in Solid Ethanolamine
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2019-10-08 , DOI: 10.1021/acs.cgd.9b00836 Michela Romanini 1 , Philippe Negrier 2 , Pragya Tripathi 1 , Kyriaki-Marina Lira 3 , Dimitrios Gournis 3 , Maria Barrio 1 , Luis Carlos Pardo 1 , Josep Lluís Tamarit 1 , Roberto Macovez 1
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2019-10-08 , DOI: 10.1021/acs.cgd.9b00836 Michela Romanini 1 , Philippe Negrier 2 , Pragya Tripathi 1 , Kyriaki-Marina Lira 3 , Dimitrios Gournis 3 , Maria Barrio 1 , Luis Carlos Pardo 1 , Josep Lluís Tamarit 1 , Roberto Macovez 1
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We employ calorimetry, Rietveld refinement of X-ray powder diffraction, broadband dielectric spectroscopy, and molecular dynamics simulations to investigate the phase behavior, crystal structure, dc conductivity, and dielectric response of the condensed phases of ethanolamine (EAM), an ethane derivative with two distinct hydrogen-bonding groups. EAM is found to exhibit, besides its stable crystal phase, a metastable crystalline phase obtained from the supercooled liquid. The metastable phase can only be maintained at low temperature; upon heating, an irreversible exothermic transformation to the stable crystal structure takes place at 210 K, with a low transition enthalpy of ca. 2.4 J/g. The observed polymorphism is accompanied by differences in the molecular conformation and degree of structural order. Each EAM molecule participates in six hydrogen bonds in both crystalline phases. While the stable phase is fully ordered, the metastable phase appears to be characterized by a statistical disorder in the position of the hydrogen atoms and thus of the intramolecular conformation and intermolecular hydrogen bonding. Our molecular dynamics simulations suggest that such disorder is dynamic in character and allow analyzing the dynamic hydrogen-bonding motif of the metastable phase in terms of composition, length, and energy of the hydrogen bonds, and molecular conformations involved. Charge conduction is mainly ionic in both crystalline phases and exhibits the typical temperature dependence of disordered solid electrolytes, rather than crystalline ones. Dielectric characterization indicates that, upon crystallization of liquid EAM, a small fraction of the sample (approximately 5%) remains amorphous, a situation similar to that reported for other hydrogen-bonded systems such as glycerol and n-butanol.
中文翻译：
固体乙醇胺中具有构象异构和不完全结晶的多态性
我们采用量热法，X射线粉末衍射的Rietveld精炼，宽带介电谱和分子动力学模拟来研究乙醇胺（EAM）的乙醇衍生物（EAM）的缩合相的相行为，晶体结构，直流电导率和介电响应。两个不同的氢键基团 发现EAM除了表现出稳定的结晶相外，还显示出从过冷液体中获得的亚稳态结晶相。亚稳相只能保持在低温下；加热后，在210 K发生不可逆的放热转变为稳定的晶体结构，跃迁焓低至约。2.4焦耳/克。观察到的多态性伴随着分子构象和结构顺序程度的差异。每个EAM分子在两个结晶相中都参与六个氢键。虽然稳定相是完全有序的，但亚稳态相的特征是氢原子位置的统计无序，因此分子内构象和分子间氢键也无统计学意义。我们的分子动力学模拟表明，这种无序现象是动态的，并可以从组成，长度和氢键能量以及所涉及的分子构象方面分析亚稳相的动态氢键基序。电荷传导在两个结晶相中都主要是离子性的，并且表现出无序固体电解质的典型温度依赖性，而不是结晶性电解质。介电特性表明，在液体EAM结晶后，正丁醇。
更新日期：2019-10-10
中文翻译：
固体乙醇胺中具有构象异构和不完全结晶的多态性
我们采用量热法，X射线粉末衍射的Rietveld精炼，宽带介电谱和分子动力学模拟来研究乙醇胺（EAM）的乙醇衍生物（EAM）的缩合相的相行为，晶体结构，直流电导率和介电响应。两个不同的氢键基团 发现EAM除了表现出稳定的结晶相外，还显示出从过冷液体中获得的亚稳态结晶相。亚稳相只能保持在低温下；加热后，在210 K发生不可逆的放热转变为稳定的晶体结构，跃迁焓低至约。2.4焦耳/克。观察到的多态性伴随着分子构象和结构顺序程度的差异。每个EAM分子在两个结晶相中都参与六个氢键。虽然稳定相是完全有序的，但亚稳态相的特征是氢原子位置的统计无序，因此分子内构象和分子间氢键也无统计学意义。我们的分子动力学模拟表明，这种无序现象是动态的，并可以从组成，长度和氢键能量以及所涉及的分子构象方面分析亚稳相的动态氢键基序。电荷传导在两个结晶相中都主要是离子性的，并且表现出无序固体电解质的典型温度依赖性，而不是结晶性电解质。介电特性表明，在液体EAM结晶后，正丁醇。
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