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

## TL;DR

This study explores how molybdenum interacts with oximes and hydroxylamines, revealing new chemical mechanisms that could improve uranium extraction from seawater.

## Contribution

The first isolation of a Mo(VI)–oxido–hydroxylamido complex and its implications for uranium extraction materials.

## Key findings

- A new Mo(VI)–oxido–hydroxylamido complex was isolated and characterized.
- The Mo(VI) reduction mechanism was clarified using experimental and computational methods.
- H3pidiox is hydrolytically unstable with [MoVIO4]2– at pH 8.0, suggesting minimal degradation of uranium extraction materials in seawater.

## Abstract

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 NH2OH 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,
[MoVI(O)­(η2-NH2O)]3+, specifically [MoVI(O)­(η1,η1,η1-pidiox-O,N,O′)­(η2-NH2O)­(H2O)], formed via hydrolysis of (2Z,6Z)-piperidine-2,6-dione dioxime (H3pidiox) by
Mo­(VI). Τhis discovery enabled us to elucidate the long-standing
mechanism of Mo­(VI) conversion to MoII–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 [MoII(η1,η1,η1-Hpidiox-O,N,O′)­(κ1-NO)­(η2-NH2O)­(OH2)]. In parallel,
we show that H3pidiox, a ligand employed in uranyl extraction
from seawater, undergoes hydrolysis by [MoVIO4]2– only upon formation of the complex cis-[MoVIO2(pidiox)]+.
However, this complex is hydrolytically unstable at pH 8.0, suggesting
that [MoVIO4]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.