Aqueous Solvation of SmI₂: A Born–Oppenheimer Molecular Dynamics Density Functional Theory Cluster Approach

Abstract

We report the results of Born-Oppenheimer molecular dynamics (BOMD) simulations on the aqueous solvation of the SmI molecule at room temperature using the cluster microsolvation approach including 32 water molecules. The electronic structure calculations were done using the M062X hybrid exchange-correlation functional in conjunction with the 6-31G** basis sets for oxygen and hydrogen. For the iodine and samarium atoms the Stuttgart-Köln relativistic effective-core potentials were utilized with their associated valence basis sets. Starting from the optimized geometry of SmI embeded in the microsolvation environment, we find a swift substitution of the iodine ions by eight tightly bound water molecules around Sm(II). Through the Sm-O radial distribution function and the evolution of the Sm-O distances, the present study predicts a first rigid Sm(II) solvation shell from 2.6 to 3.4 Å, whose integration leads to a coordination number of 8.4 water molecules, and a second softer solvation sphere from 3.5 to ca. 6 Å. The Sm(II)-O radial distribution function is in excellent agreement with that reported for Sr from EXAFS studies, a fact that can be explained because Sr and Sm have almost identical ionic radii (ca. 1.26 Å) and coordination numbers: 8 for Sr and 8.4 for Sm. The theoretical EXAFS spectrum was obtained from the BOMD trajectory and is discussed in the light of the experimental spectra for Sm(III). Once microsolvation is achieved, no water exchange events were found to occur around Sm, in agreement with the experimental data for Eu (which has a nearly identical charge-to-ionic radius relation as Sm), where the mean residence time of a water molecule in [Eu(HO)] is known to be ca. 230 ps.

Experimental and Theoretical Studies on the Implications of Halide-Dependent Aqueous Solvation of Sm(II)

“…Increasing the amount of water beyond 20 equiv led to increased conductance, consistent with the initiation of iodide displacement from the inner sphere. This experimental finding is supported by recent studies by Ramírez-Solís and co-workers who employed Born–Oppenheimer molecular dynamics (BOMD) simulations demonstrating the liberation of iodide ligands from the inner-sphere of SmI 2 upon solvation by water …”

Ab initiomolecular dynamics studies of hydroxide coordination of alkaline earth metals and uranyl

“…Recently, molecular dynamics simulations (MD) have gained popularity as method for investigating such dynamical processes. [20][21][22][23][24] Ab Initio Molecular Dynamics (AIMD), in the form of Born-Oppenheimer Molecular Dynamics (BOMD) or Car-Parrinello Molecular Dynamics (CPMD) [25][26][27] uses quantum chemical techniques to determine interatomic interactions. One of the main advantages of AIMD is that it can be used to study chemical bond-breaking and formation, 28 as such it has been used to study proton transport through water, 29 hydrogen bonding 30 and the microsolvation of ions.…”

A combined NMR and DFT study of conformational dynamics in lanthanide complexes of macrocyclic DOTA-like ligands

“…Theoretical calculations can provide detailed information about the mechanism of dynamic processes at the molecular level experienced by lanthanide(III) complexes in solution. Both classical 30 and ab initio [31][32][33] molecular dynamics (AIMD) have been used to investigate lanthanide(III) complexes. However, the parametrization of force fields to be used for f-block elements is not a trivial task.…”