Structure of Aqueous CaCl2 Solutions by X-ray Scattering and Density Functional Theory

We report a structure analysis of aqueous calcium chloride solutions as a function of concentration at 298 ± 0.5 K by X-ray scattering. The radial distribution functions (RDFs) and theoretical partial radial distribution functions for O–O, Ca–O, Cl–O, Ca–Cl atom pairs are obtained from precise diffr...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Veröffentlicht in:Russian Journal of Physical Chemistry A 2022-04, Vol.96 (Suppl 1), p.S68-S76
Hauptverfasser: Wang, Guangguo, Zhou, Yongquan, Toshio, Yamaguchi, Liu, Hongyan, Zhu, Fayan, Wu, Zhijian
Format: Artikel
Sprache:eng
Schlagworte:
Online-Zugang:Volltext
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Beschreibung
Zusammenfassung:We report a structure analysis of aqueous calcium chloride solutions as a function of concentration at 298 ± 0.5 K by X-ray scattering. The radial distribution functions (RDFs) and theoretical partial radial distribution functions for O–O, Ca–O, Cl–O, Ca–Cl atom pairs are obtained from precise diffraction data processing. The Ca–O(I) distance is 0.243–0.241 nm and the coordination number ( CN ) is from 6.7 to 6.2 in the first hydration shell, which indicates an octahedron hydration geometry. The Ca 2+ possesses the second hydration shell with the Ca–O(II) distance range of 0.485–0.480 nm and the coordination number of 13–8. The Ca–Cl distance is 0.295 nm, while the coordination number is only 0.15, which confirms the lack of the virtual absence of Ca 2+ –Cl – contact ion pairs (CIP) even at high concentrations. However, the Ca–O–Cl distance and the coordination number are 0.395–0.387 nm and 1.2–1.9, respectively. The principal change of concentration seems to be the entry of numerous numbers of Cl – ions into the second hydration shell around Ca 2+ , thus forming the Ca 2+ –OH 2 –Cl – solvent-shared ion pairs (SIP). Effects of concentration on the structure of the solutions were also discussed. Meantime, to verify the accuracy of the experiment results, we got the most stable structure of CaCl 2 (H 2 O) 6 clusters by density functional theory (DFT). Then, we find that the distance of Ca–O(I) is 0.236 nm in the most stable structure and the chloride and calcium ions are associated in the form of SIP. DFT calculations were found to be in general accordance with the experimental findings. The results show that a clear picture of the structure of the aqueous CaCl 2 solution has been acquired.
ISSN:0036-0244
1531-863X
DOI:10.1134/S0036024422140242