Density Functional Theory Investigations on the Mechanism of Formation of Pa(V) Ion in Hydrous Solutions

• Main Authors: Jun Ma, Chuting Yang, Jun Han, Jie Yu, Sheng Hu, Haizhu Yu, Xinggui Long
• Format: Article
• Language: English
• Published: MDPI AG 2019-03-01
• Series: Molecules
• Subjects: Pa(V); hydrous solutions; density functional theory (DFT); mechanism
• Online Access: https://www.mdpi.com/1420-3049/24/6/1169

Due to the enormous threat of protactinium to the environment and human health, its disposal and chemistry have long been important topics in nuclear science. [PaO(H₂O)₆]³⁺ is proposed as the predominant species in hydrous and acidic solutions, but little is known about its formation mechanism. In this study, density functional theory (DFT) calculations demonstrate a water coordination-proton transfer-water dissociation mechanism for the formation of PaO³⁺ in hydrous solutions. First, Pa(V) ion preferentially forms hydrated complexes with a coordination number of 10. Through hydrogen bonding, water molecules in the second coordination sphere easily capture two protons on the same coordinated H₂O ligand to form [PaO(H₂O)₉]³⁺. Water dissociation then occurs to generate the final [PaO(H₂O)₆]³⁺, which is the thermodynamic product of Pa(V) in hydrous solutions.