Spectroscopic and Structural Characterization of Water-Shared Ion-Pairs in Aqueous Sodium and Lithium Hydroxide
Spectroscopic and Structural Characterization of Water-Shared Ion-Pairs in Aqueous Sodium and Lithium Hydroxide
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DOI：
10.1021/acs.jpcb.0c10564
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发表时间：
2021-01-29
影响因子：
3.3
通讯作者：
Ben-Amotz, Dor
中科院分区：
文献类型：
--
作者：
de Oliveira, Denilson Mendes;Bredt, Aria J.;Ben-Amotz, Dor
通过结合拉曼多元曲线分辨（Raman-MCR）实验和从头算分子动力学（AIMD）模拟来阐明NaOH和LiOH水溶液中形成的离子对的结构。结果扩展了先前的研究结果，揭示了最初形成的离子对主要是水共享的，氢氧根离子保留其完整的第一水合壳层，而直接接触离子配对仅在较高浓度下才变得显着。我们的研究结果证实了以前的实验和模拟表明更大的离子配对在水溶液中的LiOH比NaOH以及在高温下。我们的研究结果进一步表明，NaOH和LiOH离子配对自由能有一个近似线性（而不是平方根）依赖于离子浓度（在摩尔范围内），与正熵和熵，随着浓度的增加，从而意味着水介导的相互作用的热力学不赞成和熵有利于离子对的形成。
The structures of the ion-pairs formed in aqueous NaOH and LiOH solutions are elucidated by combining Raman multivariate curve resolution (Raman-MCR) experiments and ab initio molecular dynamics (AIMD) simulations. The results extend prior findings to reveal that the initially formed ion-pairs are predominantly water-shared, with the hydroxide ion retaining its full first hydration-shell, while direct contact ion-pairing only becomes significant at higher concentrations. Our results confirm previous experiments and simulations indicating greater ion-pairing in aqueous LiOH than NaOH as well as at high temperatures. Our results further imply that NaOH and LiOH ion-pairing free energies have an approximately linear (rather than square-root) dependence on ion concentration (in the molar range), with positive enthalpies and entropies that increase with concentration, thus implying that water-mediated interactions enthalpically disfavor and entropically favor ion-pair formation.