Molecular Dynamics Simulations of Complexation of Am(III) with a Preorganized Dicationic Ligand in an Ionic Liquid

Abstract

Preorganized ligands with imidazolium arms have been found to be highly selective in extracting Am­(III) into ionic liquids (ILs), but the detailed structure and mechanism of the complexation process in the ionic solvation environment are unclear. Here, we carry out molecular dynamics simulation of the complexation of Am­(III) with a preorganized 1,10-phenanthroline-2,9-dicarboxamide complexant (L) functionalized with alkyl chains and imidazolium cations in the butylmethylimidazolium bistriflimide ([BMIM]­[NTf2]) IL. Both Am:L (1:1) and Am:L2 (1:2) complexes are examined. In the absence of the ligand, Am­(III) is found to be coordinated by six NTf2 anions via nine O donors in the first solvation shell. In the Am:L complex, Am­(III) is coordinated to the ligand via two O donors and four NTf2 anions via seven O donors in the first coordination shell. In the Am:L2 complex, Am­(III) is coordinated to the two ligands via four O donors and four NTf2 anions via five O donors. The imidazolium arms of the ligands play an important role in the secondary solvation environment by attracting NTf2 anions closer to the metal center. As a result, we find that the binding free energy for the second L2+ ligand is twice that for the first L2+ ligand, making the Am:L2 complex significantly more stable than the Am:L complex. This work highlights the multiple factors and tunability in using preorganized ligands with charged functional groups in an ionic solvation environment, which could hold the key to achieving desired selectivity in ion extraction efficiency.

Recent Advances in the Study of Trivalent Lanthanides and Actinides by Phosphinic and Thiophosphinic Ligands in Condensed Phases

“…Wipff et al [34] combined experiments and molecular dynamics simulations to explore the complexes of uranyl in ionic liquids, and found that nitrate ions and chloride ions could compete to coordinate with uranyl ions. Jiang and co-workers [35] simulated the dynamics of the preorganized 1,10-phenanthroline-2,9-dicarboxamide ligand (L) bound with Am 3+ cation in the butylmethylimidazolium bistriflimide ([BMIM][NTf 2 ]) ionic liquid. For both Am:L (1:1) and Am:L 2 (1:2) complexes, it was found that the secondary solvation environment was influenced by the imidazolium arms of the ligands attracting NTf 2 anions near the metal ion.…”

Atomistic Insights into Structure and Dynamics of Neodymium(III) Complexation with a Bis-lactam Phenanthroline Ligand in the Organic Phase

“…Computational studies on REE complexes with organic ligands in solvents or solutions are typically carried out at the quantum chemistry level with an implicit solvation model or with a force field and an explicit solvation model. ,− The former approach can miss important interactions and dynamics between the solute and the solvent, whereas the latter depends on the quality of the force field. First principles molecular dynamics (FPMD) simulations can nicely fill this gap by providing an explicit solvation environment and avoiding the issues of fitting force-field parameters.…”