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Accurate Determination of the Quantity and Spatial Distribution of Counterions around a Spherical Macroion
Author(s) -
Chen Jiahui,
Bera Mrinal K.,
Li Hui,
Yang Yuqing,
Sun Xinyu,
Luo Jiancheng,
Baughman Jessi,
Liu Cheng,
Yao Xuesi,
Chuang Steven S. C.,
Liu Tianbo
Publication year - 2021
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202013806
Subject(s) - ion , counterion , cluster (spacecraft) , chemistry , polyoxometalate , scattering , crystallography , anomalous scattering , physics , optics , organic chemistry , computer science , programming language , biochemistry , catalysis
Abstract The accurate distribution of countercations (Rb + and Sr 2+ ) around a rigid, spherical, 2.9‐nm size polyoxometalate cluster, {Mo 132 } 42− , is determined by anomalous small‐angle X‐ray scattering. Both Rb + and Sr 2+ ions lead to shorter diffuse lengths for {Mo 132 } than prediction. Most Rb + ions are closely associated with {Mo 132 } by staying near the skeleton of {Mo 132 } or in the Stern layer, whereas more Sr 2+ ions loosely associate with {Mo 132 } in the diffuse layer. The stronger affinity of Rb + ions towards {Mo 132 } than that of Sr 2+ ions explains the anomalous lower critical coagulation concentration of {Mo 132 } with Rb + compared to Sr 2+ . The anomalous behavior of {Mo 132 } can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion–cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion–{Mo 132 } interaction.