Expansion of the Na3MIII(Ln/An)6F30 Series: Incorporation of Plutonium into a Highly Robust and Stable Framework

Abstract

Na_nMAn₆F₃₀ is an extremely versatile framework structure for incorporating tetravalent actinides (An) and cerium along with divalent or trivalent d-metals (M); moreover, the structure exhibits a high resistance to harsh chemical conditions. This extreme robustness can potentially be exploited for the sequestration of plutonium in a stable matrix; however, no Na_nMPu₆F₃₀ compounds have been reported so far. Herein, we present four new plutonium fluorides that have been prepared as single crystals by mild hydrothermal synthesis methods. Structural characterizations revealed their compositions to be Na₃AlPu₆F₃₀, Na₃FePu₆F₃₀, Na₃CoPu₆F₃₀, and Na_2.4Mn_1.6Pu₆F₃₀. Surprisingly, in the plutonium series, it was found that Co²⁺ and Mn²⁺ precursors oxidized to form Na₃Co^IIIPu₆F₃₀ and Na_2.4Mn^II/III_1.6Pu₆F₃₀, whereas the analogous reactions for cerium result in reduction of the transition metal, even when beginning with a M³⁺ precursor. While cerium is often used as a surrogate for plutonium, this work serves as an example that deviations between their chemistries do occur.