Investigation into the fundamental solid-state chemistry of actinide elements: Synthesis and characterization of ternary and quaternary actinide chalcogenide compounds

The use of molten alkali metal polysulfide fluxes has had a profound impact on the synthesis of complex multinary chalcogenide compounds. This method has been used to synthesize numerous quaternary transition metal and rare-earth chalcophosphate compounds. Relatively little information is known about the solid-state chemistry of actinide elements in a chalcogen environment. The synthesis and characterization of the first quaternary thorium, uranium, and plutonium thiophosphate compounds will be discussed. Three uranium, five thorium, and five plutonium thiophosphate compounds have been characterized by single crystal X-ray diffraction, Raman spectroscopy, and diffuse reflectance UV-visible-NIR spectroscopy. These compounds exhibit structures ranging from three-dimensional extended networks found in Cs₈U₅(P ₃S₁₀)₂(PS₄)₆ to one-dimensional chains found in K₃Pu(PS₄)₂. A ternary plutonium selenide, KPu₃Se₈, has also been characterized using X-ray diffraction and X-ray absorption spectroscopy. The coordination environments of the actinide metals in these compounds are examined. Preferences in coordination geometry and metal oxidation state are discussed, and a consistent series of metal-chalcogen distances is developed.