Although in recent times, the task-specific ionic liquid HbetNTf2 has been extensively used for direct dissolution of many solid metal oxides like PuO2, the mechanism of the dissolution is still not clear. In this work, density functional theory is used to investigate the dissolution mechanism of PuO2, a frequently encountered useful solid in the nuclear industry. By comparison of reaction energies of plausible pathways of dissolution with the cohesive energy of solid PuO2, four energetically feasible schemes are identified. These routes are based on the complex formation of Pu4+ with deprotonated Hbet+, water, and/or NTf2- ligands. Either four or six deprotonated Hbet+ ligands coordinate directly to Pu4+, while in situ generated water molecules further stabilize the complexes. Crucially, participation of the anionic NTf2- ligand, in either the first or second solvation shell, is found to be essential for providing the requisite reaction energy to overcome the lattice energy required to dissolve the solid PuO2. Energy decomposition analysis elucidates the nature of metal-ligand interactions; RDG and NCI analyses unfold the role of noncovalent interactions in complex formation, whereas Mulliken and CHELPG charge analyses reveal the extent of metal-to-ligand charge transfer and coordinate bonding.
Yadav et al. (Tue,) studied this question.