Structure of the Nearest Environment of Na + , K + , Rb + , and Cs + Ions in Oxygen-Containing Solvents
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Structure of the Nearest Environment of Na+, K+, Rb+, and Cs+ Ions in Oxygen-Containing Solvents P. R. Smirnova,* a
Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, 153045 Russia *e-mail: [email protected] Received March 3, 2020; revised June 3, 2020; accepted June 10, 2020
Abstract—The review generalizes and analyzes published data on different methods of studying structural characteristics of the solvation environment of alkali metal ions (except for Li+) in various electron-donor oxygencontaining solvents. Coordination numbers of alkali metal ions, interspecies distances, and types of ion association are discussed. The solvation structures of alkali metal cations in water and some nonaqueous systems are compared. The number of solvent molecules and the distance between the cation and oxygen atom of solvent molecule in the first coordination sphere are independent of physicochemical properties of the solvent. Keywords: coordination number, interspecies distance, ion pair
DOI: 10.1134/S1070363220090169 1. Introduction 2. Solvation Structure of Na+ Ion 3. Solvation Structure of K+ Ion 4. Solvation Structure of Rb+ Ion 5. Solvation Structure of Cs+ Ion 6. Conclusions
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1. INTRODUCTION Electrolyte solutions have a variety of applications in different fields. Development and improvement of inexpensive electric energy accumulators constitute quite important problems. The scope of application of lithium ion batteries continuously increases; however, their large-scale production is limited by deficiency of lithium. In this respect, sodium ion batteries seem to be most promising. This is only a particular case of using electrolyte solutions in industry. They are widely used in medicine, agriculture, and other fields. Optimization of the composition of electrolyte solutions to improve the efficiency of their specific application requires knowledge of their properties and structure. Physicochemical properties of electrolyte solutions depend on the properties of the solvent, concentration of ions, and their characteristics. The effect of ions on processes occurring in solutions is determined by their solvation environment and ordering of ionic and
molecular species that surround these ions. The structure of solutions is extensively studied in various chemical research centers. Many structural characteristics of solutions, including solutions of inorganic electrolytes in aqueous systems, have already been determined. Nevertheless, such important parameters as coordination numbers (CN) and interspecies distances for some ions remain unknown. There is even more ambiguity in the description of second coordination spheres or ion associates. The number of open questions regarding nonaqueous electrolyte solutions is considerably larger. The present review systematizes information on quantitative structural characteristics of the nearest environment of alkali metal ions (except for Li+ whose solvate structure in different solvents has been considered in [1]) reported after
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