物理化学学报 >> 2018, Vol. 34 >> Issue (5): 483-491.doi: 10.3866/PKU.WHXB201709111

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RbCl和CsCl水溶液结构的X射线散射及经验势结构精修模拟

周永全1,曾我良枝2,山口敏男2,房艳1,房春晖1,*()   

  1. 1 中国科学院青海盐湖研究所,青海西宁810008
    2 福冈大学理学院化学系,福冈814-0180,日本
  • 收稿日期:2017-08-07 发布日期:2018-01-24
  • 通讯作者: 房春晖 E-mail:fangch@isl.ac.cn
  • 基金资助:
    青海省自然科学基金(2015-ZJ-945Q);中国科学院青年创新促进会(2017467)

Structure of Aqueous RbCl and CsCl Solutions Using X-Ray Scattering and Empirical Potential Structure Refinement Modelling

Yongquan ZHOU1,Yoshie SOGA2,Toshio YAMAGUCHI2,Yan FANG1,Chunhui FANG1,*()   

  1. 1 Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, Qinghai Province, P. R. China
    2 Department of Chemistry, Faculty of Science, Fukuoka University, 8-19-1 Nanakuma, Jonan, Fukuoka 814-0180, Japan
  • Received:2017-08-07 Published:2018-01-24
  • Contact: Chunhui FANG E-mail:fangch@isl.ac.cn
  • Supported by:
    the Natural Science Foundation of Qinghai Province, China(2015-ZJ-945Q);Youth Innovation Promotion Association, CAS, China(2017467)

摘要:

采用X射线散射法研究了RbCl和CsCl水溶液的结构,利用基于经验势的结构精修(EPSR)方法获得了溶液中的水合Cl-、Rb+、Cs+、离子缔合及本体水的对径向分布函数、配位数分布及空间密度分布(3D结构)等结构信息。在水溶液中,Cl-具有相对稳定的6水合结构,其水合距离为0.321 nm,外加阳离子对其水合作用的影响不明显。7.3 ± 1.4个水分子与Rb+水合,其特征水合距离为0.297 nm,8.4 ± 1.6个水分子与Cs+水合其水合距离为0.312 nm。Cs+不具有第二水合层,而Rb+表现出了更强的水合能力,具有较明显的第二水合层。Cl-、Rb+及Cs+常被认为是“结构破坏”型离子。从微观角度来看这种所谓的“结构破坏”主要体现在破坏了本体水分子的第二水合层保持四面体构型的趋势。RbCl和CsCl水溶液中部分存在着Rb-Cl和Cs-Cl直接接触离子对,在1.0 mol·dm-3的溶液中Rb-Cl及Cs-Cl的特征距离分别为0.324和0.336 nm,溶剂分割离子对的距离则都在0.6 nm左右。相对于Cs+,Rb+与Cl-离子之间表现出了更强的缔合能力。

关键词: RbCl, CsCl, 溶液结构, X射线散射, EPSR

Abstract:

X-ray scattering measurements were performed on 1.0 mol·dm-3 RbCl and CsCl aqueous solutions. The X-ray structure factors were subjected to empirical potential structure refinement to extract detailed structural information on hydrated Cl-, Rb+, Cs+, and ion association, as well as bulk water, in terms of the individual site-site pair correlation functions, coordination number distributions, and spatial density functions (three-dimensional structure). Cl- is found to have a relatively stable six-fold coordination of water molecules with a Cl--H2O distance of 0.321 nm, and without a significant cation effect on its local structure. Rb+ is surrounded on an average by 7.3 ± 1.4 water molecules with a Rb+-H2O distance of 0.297 nm, whereas 8.4 ± 1.6 water molecules hydrate Cs+ at a Cs+-H2O distance of 0.312 nm. It is likely that Rb+ has a stronger hydration shell than Cs+, as evidenced by the presence of the second hydration shell of the former. Contact ion-pairs are partially formed in both solutions and characterized by the Rb+-Cl- and Cs+-Cl- distances of 0.324 nm and 0.336 nm. The solvent-separated ion pairs for both ions are discernible at around 0.6 nm. Rb+ has a stronger electrostatic interaction and hence a relatively stronger ion association with Cl- than Cs+.

Key words: RbCl, CsCl, Solution structure, X-ray scattering, EPSR

MSC2000: 

  • O641