A quantum-chemistry and molecular-dynamics study of non-covalent interactions between tri-n-butyl phosphate and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

The complicated behavior of extractants in ionic liquids (ILs) has posed great challenges for radionuclides separation and purification. In this regard, a theoretical investigation of combining quantum chemical (QC) calculations and molecular dynamics (MD) simulations was performed to explore the local structures, intermolecular interactions, and dynamic behaviors between the tri-n-butyl phosphate (TBP) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C₄mimTf₂N) system. It is demonstrated that the ion pair of C₄mimTf₂N rather than the separated ions is more favored either in the gas phase or in solution. Their interaction with TBP is primarily dominated by the electrostatic interaction in most cases, while the dispersion and induction ones are non-negligible. Simultaneously, the intermolecular changes the atom charges of TBP and C₄mimTf₂N. Similar local structures have been accessible by both QC and MD calculations. It is revealed that the local structures and intermolecular interactions are strongly dependent on the TBP concentration.