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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions
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Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions

机译：抗衡离子对稀水溶液中镧离子水合结构的影响

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摘要

A synergic approach combining molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) has been used to investigate diluted (0.1 M) aqueous solutions of two lanthanide ions (Ln(3+)), namely, La3+ and Dy3+, with triflate, nitrate, and bis(trifluoromethylsulfonyl)imide (Tf2N- as counterions. The different complexing ability of the three anions has been highlighted by the analysis of the MD simulations: Tf2N- does not form inner sphere complexes, while a small amount of triflate coordinates both the La3+ and Dy3+ cations in their first solvation shell. On the other hand, the nitrate ion is almost absent in the La3+ first coordination sphere, while forming contact ion pairs with Dy3+. Both lanthanide ions are found to preferentially interact with the water molecules, and the total number of oxygen atoms coordinating the Ln(3+) cations in their first solvation sphere is the same in all of the solutions, regardless of whether they belong to water molecules or to the counterion. The presence of counterions in the cation first or second shell changes neither the first shell distance nor the symmetry of the hydration complex formed in solution. The MD results have been confirmed by comparison with the Ln K-edge XAS experimental data, and the quantitative analysis of the extended X-ray absorption fine structure (EXAFS) spectra of the three salt solutions has provided a definite proof of the accuracy of the force field employed in the simulations and of the MD structural result. The anion-water and water-water hydrogen bond lifetimes have been analyzed highlighting the slow down effect of the triflate, nitrate, and Tf2N- anions on the hydrogen bond dynamics in the Ln(3+) first solvation shell, with the effect being stronger in the Dy3+ solutions, due to the higher charge density of the Dy3+ ion as compared to La3+.
机译：组合分子动力学（MD）模拟和X射线吸收光谱（XAs）的协同方法已被用于研究两种镧系元素离子（LN（3+））的稀释（0.1M）水溶液，即La3 +和DY3 +，具有Triflate，硝酸盐和双（三氟甲基磺酰基）酰亚胺（TF2N-作为抗衡离子。通过分析MD模拟的分析，突出了三个阴离子的不同络合能力：TF2N-不形成内部球形复合物，而少量的三种三种在其第一溶剂化壳中坐标。另一方面，在La3 +第一配位球中几乎不存在硝酸根，同时形成与DY3 +的接触离子对。发现镧系元素都优先与水相互作用在所有溶液中，在其第一溶剂化球中协调LN（3+）阳离子的氧原子的总数是相同的，无论它们是否属于水分子或核心rion。阳离子第一或第二壳体中的抗衡离子均不改变第一壳距离，也不会使在溶液中形成的水​​化复合物的对称性。通过与LN K-Edge XAS实验数据进行比较确认了MD结果，并且三种盐溶液的延长X射线吸收细结构（EXAFS）光谱的定量分析提供了一个明确的准确性证明在模拟和MD结构结果中使用的力场。已经分析了阴离子 - 水和水 - 水氢键寿命，突出了Triflate，硝酸盐和TF2NIONs对LN（3+）第一溶剂化壳中的氢键动力学的慢效应，其效果更强在DY3 +溶液中，与LA3 +相比DY3 +离子的较高电荷密度。

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