Stable Salt–Water Cluster Structures Reflect the Delicate Competition between Ion–Water and Water–Water Interactions

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• 作者：Cheng-Wen Liu ; Feng Wang ; Lijiang Yang ; Xin-Zheng Li ; Wei-Jun Zheng ; Yi Qin Gao
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：January 23, 2014
• 年：2014
• 卷：118
• 期：3
• 页码：743-751
• 全文大小：577K
• ISSN：1520-5207

文摘

How salts affect water structure is an important topic in many research fields. Salt鈥搘ater clusters can be used as model systems to extract interaction information that is difficult to obtain directly from bulk solutions. In the present study, integrated tempering sampling1,2 molecular dynamics (MD) are combined with quantum mechanics (QM) calculations to overcome the sampling problem in cluster structure searches. We used LiI(H₂O)_n and CsI(H₂O)_n as representatives to investigate the microsolvation of ion pairs. It was found that Li⁺鈥揑^{鈥?/sup> and Cs+鈥揑鈥?/sup> ion pairs interact with water molecules in very different ways, and the corresponding salt鈥搘ater clusters have distinctly different structures. LiI strongly affects water鈥搘ater interactions, and the LiI(H₂O)_n (n 鈮?5) clusters build around a Li+(H₂O)₄ motif. CsI only slightly perturbs the water cluster structure, and CsI(H₂O)_n favors the clathrate-like structure when n = 18 or 20. Consistent with the law of 鈥渕atching water affinities鈥? Li+ and I鈥?/sup> are more easily separated by solvent molecules than the Cs+鈥揑鈥?/sup> ion pair.}