Modeling Mo(VI)═O Biologically Related Interactions with Oximes and Hydroxylamines: Implications for Uranium Seawater Extraction

High Resolution Image Download MS PowerPoint Slide Molybdenum enzymes play a crucial role in the nitrogen cycle processes. However, the mechanism of Mo(VI) reduction by hydroxylamine/oximes and its implications for oxime-based sorbents remain unclear. For decades, it has been widely accepted that the reaction of NH 2 OH with Mo(VI) consistently results in the molybdenum reduction. This study presents evidence that challenges the prevailing view by isolating the first Mo(VI)–oxido–hydroxylamido complex, [Mo VI (O)(η 2 -NH 2 O)] 3+, specifically [Mo VI (O)(η 1,η 1,η 1 -pidiox- O, N, O ′)(η 2 -NH 2 O)(H 2 O)], formed via hydrolysis of (2 Z,6 Z )-piperidine-2,6-dione dioxime (H 3 pidiox) by Mo(VI). Τhis discovery enabled us to elucidate the long-standing mechanism of Mo(VI) conversion to Mo II –NO through a combination of experimental techniques (NMR, ESI-MS, XPS, FT-IR) and density functional theory (DFT) calculations. This comprehensive approach provided new insight into molybdenum redox behavior and unambiguously confirmed the Mo(II) oxidation state in [Mo II (η 1,η 1,η 1 -Hpidiox- O, N, O ′)(κ 1 -NO)(η 2 -NH 2 O)(OH 2 )]. In parallel, we show that H 3 pidiox, a ligand employed in uranyl extraction from seawater, undergoes hydrolysis by [Mo VI O 4 ] 2– only upon formation of the complex cis -[Mo VI O 2 (pidiox)] + . However, this complex is hydrolytically unstable at pH 8.0, suggesting that [Mo VI O 4 ] 2– is unlikely to degrade uranium oxime-based extraction materials in seawater. This study provides fundamental insight into molybdenum–oxime reactivity, offering a molecular basis for designing robust oxime-functionalized materials for efficient and durable uranium seawater extraction processes.