Synthesis and structural characterization of actinide(U(VI) or Pu(IV))-monoamide compounds
Résumé
Crystallographic studies play a key role in coordination chemistry. It provides information on the coordination mode, the geometry of the complex, the interaction strength between the ligand and the cation. As such, our group studies the crystallization of different actinides with monoamides considered as good models for extraction of U(VI) and Pu(IV) candidates [1,2]. Previous researches reveal that the monoamide structure has a huge impact on the uranium(VI)-plutonium(IV) selectivity and the extraction properties [3]. The single crystal syntheses and structural characterizations of actinides (U(VI), Pu(IV)) or lanthanides (Ce(IV) surrogates of Pu(IV)) complexes with four different monoamides are reported herein. To the best of our knowledge it is the first structures of tetravalent cation (Ce(IV) or Pu(IV)) with monoamide ligand. To favor crystallization, the studied monoamides are short chain ligands considered as surrogates of the real extractant molecules. The comparison of the complexes allows analyzing the impact of the nitrogen atom dissymmetry and the ramification of the carbonyl chain. For all the synthesized complexes, the structure is solved by single-crystal X-ray diffraction and the compounds are fully characterized by IR spectroscopy and EXAFS as a solid, or dissolved in an organic phase. The comparison of the results between the different solid complexes as well as the comparison between solid and liquid phases (structures, IR frequencies, and distances form EXAFS and XRD) give some hints to better understand the Actinide-monoamide systems in extraction processes.