| Abstract
| - Structural parameters of the Sr2+ and, for the first time, of the Eu2+ ions in aqueous solution were determinedby the XAFS method. For the Sr2+, the use of an improved theoretical approach led to a first shell coordinationnumber of 8.0 (3), a Sr−O distance of 2.600 (3) Å and a Debye−Waller factor of σ2 = 0.0126 (5) Å2. Theseresults were confirmed by an analysis performed with experimental phase and amplitude, extracted from thesolid reference compound [Sr(H2O)8](OH)2. The same theoretical approach was used for the analysis of theEu2+ XAFS spectra in aqueous solution. This gives a first coordination shell of Eu2+ formed by 7.2 (3) watermolecules, an Eu−O distance of 2.584 (5) Å, and a high Debye−Waller factor of σ2 = 0.0138 (5) Å2. WhereasEu3+ occurs as an equilibrium between the [Eu(H2O)8]3+ and the [Eu(H2O)9]3+ ions, Eu2+ occurs in aqueoussolution as an equilibrium between a predominant [Eu(H2O)7]2+ ion and a minor [Eu(H2O)8]2+ species.
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