Formation\nof Fully Stoichiometric, Oxidation-State\nPure Neptunium and Plutonium Dioxides from Molecular Precursors

Amidate-based ligands (<i>N</i>-(<i>tert</i>-butyl)isobutyramide, <b>ITA</b>) bind κ<sup>2</sup> to\nform homoleptic, 8-coordinate complexes with tetravalent <sup>237</sup>Np (Np(ITA)<sub>4</sub>, <b>1-Np</b>) and <sup>242</sup>Pu\n(Pu(ITA)<sub>4</sub>, <b>1-Pu</b>). These compounds complete\nan isostructural series from Th, U–Pu and allow for the direct\ncomparison between many of the early actinides with stable tetravalent\noxidation states by nuclear magnetic resonance (NMR) spectroscopy\nand single crystal X-ray diffraction (SCXRD). The molecular precursors\nare subjected to controlled thermolysis under mild conditions with\nthe exclusion of exogenous air and moisture, facilitating the removal\nof the volatile organic ligands and ligand byproducts. The preformed\nmetal–oxygen bond in the precursor, as well as the metal oxidation\nstate, are maintained through the decomposition, forming fully stoichiometric,\noxidation-state pure NpO<sub>2</sub> and PuO<sub>2</sub>. Powder X-ray\ndiffraction (PXRD), scanning transmission electron microscopy (STEM),\nand energy dispersive X-ray spectroscopy (EDS) elemental mapping supported\nthe evaluation of these high-purity materials. This chemistry is applicable\nto a wide range of metals, including actinides, with accessible tetravalent\noxidation states, and provides a consistent route to analytical standards\nof importance to the field of nuclear nonproliferation, forensics,\nand fundamental studies.