Exploring the Oxidation States of Neptunium with Schiff Base Coordination Complexes.

A pair of neptunium Schiff base coordination complexes, and { = ,'-bis[(4,4'-diethylamino)salicylidene]-1,2-phenylenediamine}, have been synthesized and analyzed by several characterization methods including single-crystal X-ray diffraction, electronic absorption, H NMR, cyclic voltammetry, and theoretical interpretation. Structural analysis reveals that and are isomorphous with the previously reported and (M = Pu, Ce, U, Th) complexes, respectively, allowing for a direct comparison across the series. The reduction of or direct synthesis from a (NpO) source shows evidence of a pentavalent neptunyl species as determined by UV/vis/NIR and H NMR spectroscopy. The synthesis of directly from a (NpO) starting material gives a similar spectrum. Theoretical analysis offers insight into the electronic structure for a better understanding of the bonding patterns and relative stability of the different oxidation states. Computational results show that the Np-L covalent interactions in are similar to those in the complex, indicating that neither the presence of the axial oxo ligands nor the oxidation state significantly modify the nature of the Np-L bonds.