title: Strengthening of the Coordination Shell by Counter Ions in Aqueous Th4+Solutions.
abstract: The presence of counterions in solutions containing highly charged metal cations can trigger processes such as ion-pair formation, hydrogen bond breakages and subsequent re-formation, and ligand exchanges. In this work, it is shown how halide (Cl-, Br-) and perchlorate (ClO4-) anions affect the strength of the primary solvent coordination shells around Th4+using explicit-solvent and finite-temperature ab initio molecular dynamics modeling methods. The 9-fold solvent geometry was found to be the most stable hydration structure in each aqueous solution. Relative to the dilute aqueous solution, the presence of the counterions did not significantly alter the geometry of the primary hydration shell. However, the free energy analyses indicated that the 10-fold hydrated states were thermodynamically accessible in dilute and bromide aqueous solutions within 1 kcal/mol. Analysis of the results showed that the hydrogen bond lifetimes were longer and solvent exchange energy barriers were larger in solutions with counterions in comparison with the solution with no counterions. This implies that the presence of the counterions induces a strengthening of the Th4+hydration shell.
authors.affiliation: Department of Physics, The University of Texas at Arlington , Arlington, Texas 76006, United States.
authors.forename: Raymond
authors.initials: R
authors.lastname: Atta-Fynn
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Bylaska
authors.affiliation: Computational Research Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Wibe A
authors.identifier: http://orcid.org/0000-0002-7114-8315
authors.initials: WA
authors.lastname: de Jong