Insights from molecular dynamics: What drives the Eu(NO3)3 aggregate formation in solvent extraction?

The study explores the formation of solvent extraction aggregates composed of Eu(NO 3 ) 3 salts with DMDOHEMA molecules solvated in n -heptane using classical molecular dynamics simulations at two Eu(NO 3 ) 3 salt concentrations, namely 0.015 and 0.126 mol L -1 . For both concentrations, the main aggregates are predominantly in the form of Eu 3 + monomers and dimers, with a higher ratio of monomers. However, increasing the Eu(NO 3 ) 3 concentration tends to increase the number of dimers. The average Eu 3 + monomer is composed of three nitrate anions and 3–4 DMDOHEMA molecules, whereas the average dimer is composed of six nitrate anions and 6 DMDOHEMA molecules. For both types of aggregates, the influence of the Eu(NO 3 ) 3 concentration has been observed only in the number of water molecules involved in each kind of aggregate. Furthermore, we demonstrated that the presence of nitrate anions and especially the number of water molecules in the polar core of the aggregates favors the formation of dimers, with various types of nitrate-water bridges. We highlighted that the dynamics of water in the vicinity of the cations, as well as the availability of ligands capable of forming hydrogen bonds within the coordination shell of nearby ions, are crucial for understanding the aggregation mechanisms. • We investigated the formation of solvent extraction aggregates composed of Eu(NO 3 ) 3 salts with DMDOHEMA molecules at two salt concentrations by molecular dynamics. • We pointed out the formation of aggregates mainly consisting of Eu 3 + monomers and dimers for which the salt concentration only affects the amount of water molecules inside. • We highlighted the dynamics of water and the availability of ligands of forming hydrogen bonds allows are the key points for understanding the aggregation mechanisms.