Molecular dynamics study of Sm2+ and Eu2+ in water with polarizable AMOEBA force field

What is it about?

In this work, we presented that Sm2+ and Eu2+, having larger ionic radii with respect to their trivalent species, obtain a lower coordination number (~8.2) in water. Although chemically counterintuitive, we showed that Sm2+ and Eu2+, having weaker interactions with water compared with Sm3+ and Eu3+, undergo a so-called "progressive/frequent water exchange" mechanism and cannot obtain a stable coordination number like their corresponding trivalent cations. We also studied the interaction of the mentioned cations with chloride in different concentrations which has not been done theoretically (and maybe experimentally as well).

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Photo by Girl with red hat on Unsplash

Photo by Girl with red hat on Unsplash

Why is it important?

Considering divalent lanthanides as a new emerging subfield of lanthanides, this work can be counted as a novel and inspirational study for strengthening this new subfield. Since divalent lanthanides are very unstable in water, their interactions and coordination environments cannot be fully pictured with experimental studies. This is due to the very fast interactions of the mentioned cations in water which makes the experimental characterization incapable of analyzing them. However, since molecular dynamics simulations allow us to study them in a very small time scale, as low as femtosecond, we can observe how these cations behave and why they obtain smaller coordination number with respect to their trivalent lanthanide cations.

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