Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (5): 483-491.doi: 10.3866/PKU.WHXB201709111

• ARTICLE • Previous Articles     Next Articles

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)

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