Structure of Aqueous CaCl2 Solutions by X-ray Scattering and Density Functional Theory
Structure of Aqueous CaCl2 Solutions by X-ray Scattering and Density Functional Theory
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DOI：
10.1134/s0036024422140242
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发表时间：
2022-04
影响因子：
0.7
通讯作者：
Guangguo Wang;Yongquan Zhou;Yamaguchi Toshio;Hongyan Liu;F. Zhu;Zhijian Wu
中科院分区：
文献类型：
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作者：
Guangguo Wang;Yongquan Zhou;Yamaguchi Toshio;Hongyan Liu;F. Zhu;Zhijian Wu
在298±0.5 K的温度下，用x射线散射分析了氯化钙水溶液的结构与浓度的关系。通过对衍射数据的精确处理，得到了O-O、Ca-O、Cl-O、Ca-Cl原子对的径向分布函数和理论部分径向分布函数。Ca-O (I)距离为0.243 ~ 0.241 nm，配位数（CN）在6.7 ~ 6.2之间，为八面体水化结构。Ca2+具有第二层水合壳，Ca-O （II）距离范围为0.485 ~ 0.480 nm，配位数为13 ~ 8。Ca-Cl距离为0.295 nm，配位数仅为0.15，证实了Ca2+ - cl接触离子对（CIP）即使在高浓度下也不存在。Ca-O-Cl的距离为0.395 ~ 0.387 nm，配位数为1.2 ~ 1.9 nm。浓度的主要变化似乎是大量的cl -离子进入Ca2+周围的第二个水化壳，从而形成Ca2+ - oh2 - cl -溶剂共享离子对（SIP）。讨论了浓度对溶液结构的影响。同时，为了验证实验结果的准确性，我们利用密度泛函理论（DFT）得到了最稳定的CaCl2(H2O)6簇结构。然后，我们发现在最稳定的结构中，Ca-O (I)的距离为0.236 nm，氯离子和钙离子以SIP形式结合。DFT计算结果与实验结果基本一致。结果表明，得到了cacl2水溶液结构的清晰图像。
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 Ca2+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 Ca2+–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 Ca2+, thus forming the Ca2+–OH2–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 CaCl2(H2O)6clusters 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 CaCl2solution has been acquired.