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<p>Efficient separation of californium from coexisting lanthanides and minor actinides remains a significant challenge in nuclear chemistry. This work systematically investigates the coordination chemistry and extraction behavior of trivalent <i>f</i>-block ions with HEHEHP (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) in nitric acid using speciation analysis and density functional theory (DFT) calculations. Thermodynamic speciation analysis indicates that M(NO<sub>3</sub>)<sup>2+</sup> dominates under medium to low acidity, providing a realistic basis for modeling extraction processes. Based on this, complexes with different metal-to-ligand ratios were constructed and systematically studied using density functional theory. Structural results show that HEHEHP preferentially coordinates to metal ions and effectively replaces hydration water. Electronic structure analysis using natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), and projected density of states (PDOS) reveals that metal-ligand interactions are mainly ionic with varying covalent contributions, following the trend <i>Cf(III) &gt; Am(III) &gt; Eu(III)</i>, associated with enhanced <i>5f</i>-orbital participation in actinides. Thermodynamic calculations show that complex formation is favorable for all three metals, with Eu(III) able to accommodate multiple ligands, Am(III) exhibiting stronger binding throughout, and Cf(III) displaying the highest affinity and greatest thermodynamic stability. Overall, the binding strength follows the order <i>Cf(III) &gt; Am(III) &gt; Eu(III)</i>, reflecting progressively stronger ligand interactions with actinides compared with lanthanides. These findings provide molecular-level insights into the extraction mechanism and offer theoretical guidance for the selective separation of Cf(III) in nitric acid systems.</p>

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Theoretical study on the coordination chemical properties of Cf(III), Am(III), and Eu(III) complexes with HEHEHP

  • 期刊论文

  • 发表日期：

    2026年6月18日

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  • Qi Cao,
  • Jiajia Yang,
  • Xiangyi Du,
  • Jia Tang,
  • Yi Wang,
  • Jixue Sui,
  • Yunyun Lu,
  • Mingzhang Lin

摘要

Efficient separation of californium from coexisting lanthanides and minor actinides remains a significant challenge in nuclear chemistry. This work systematically investigates the coordination chemistry and extraction behavior of trivalent f-block ions with HEHEHP (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester) in nitric acid using speciation analysis and density functional theory (DFT) calculations. Thermodynamic speciation analysis indicates that M(NO3)2+ dominates under medium to low acidity, providing a realistic basis for modeling extraction processes. Based on this, complexes with different metal-to-ligand ratios were constructed and systematically studied using density functional theory. Structural results show that HEHEHP preferentially coordinates to metal ions and effectively replaces hydration water. Electronic structure analysis using natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), and projected density of states (PDOS) reveals that metal-ligand interactions are mainly ionic with varying covalent contributions, following the trend Cf(III) > Am(III) > Eu(III), associated with enhanced 5f-orbital participation in actinides. Thermodynamic calculations show that complex formation is favorable for all three metals, with Eu(III) able to accommodate multiple ligands, Am(III) exhibiting stronger binding throughout, and Cf(III) displaying the highest affinity and greatest thermodynamic stability. Overall, the binding strength follows the order Cf(III) > Am(III) > Eu(III), reflecting progressively stronger ligand interactions with actinides compared with lanthanides. These findings provide molecular-level insights into the extraction mechanism and offer theoretical guidance for the selective separation of Cf(III) in nitric acid systems.