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Verma PK, Mahanty B, Bhattacharyya A, Matveev PI, Borisova NE, Kalmykov SN, Mohapatra PK. Pyridine Diphosphonate Ligand for Stabilization of Tetravalent Uranium and Neptunium in Aqueous Medium under Aerobic Conditions. Inorg Chem 2024; 63:3348-3358. [PMID: 38320960 DOI: 10.1021/acs.inorgchem.3c03840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2024]
Abstract
Though uranium is usually present in its +6 oxidation state (as uranyl ion) in aqueous solutions, its conversion to oxidation states such as +4 or +5 is a challenging task. Electrochemical reduction and axial oxo activation are the preferred methods to get stable unusual oxidation states of uranium in an aqueous medium. In previous studies, dicarboxylic acid has been used to stabilize UO2+ in aqueous alkaline solutions. In the present work, a diphosphonate ligand was chosen due to its higher complexing ability compared to that of the carboxylate ligands. Neptunium complexation studies with 2,6-pyridinediphosphonic acid (PyPOH) indicated the formation of different species at different pH values and the complexation facilitates disproportionation of NpO2+ to Np4+ and NpO22+ at pH 2. Hexavalent actinides form insoluble complexes in aqueous media at pH = 2, as confirmed by UO22+ complexation studies. The in situ complexation-driven precipitation resulted in conversion to pure Np4+ in aqueous media as the Np4+-PyPOH complex. A strong complexing ability of the PyPOH ligand toward the Np4+ ion is also seen for the stabilization of the electrochemically generated U4+ in aqueous medium under aerobic conditions. The U4+-PyPOH complex was found to be stable for 3 months. Raman, UV-vis, fluorescence, and cyclic voltametric studies along with density functional theory (DFT) calculations were done to get structural insights into the PyPOH complexes of actinides in different oxidation states.
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Affiliation(s)
- Parveen Kumar Verma
- Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
| | - Bholanath Mahanty
- Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
| | - Arunasis Bhattacharyya
- Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
| | - Petr I Matveev
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russia
| | - Nataliya E Borisova
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russia
| | - Stepan N Kalmykov
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russia
| | - Prasanta Kumar Mohapatra
- Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
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