Complexity of An chemistry in aqueous oxo-salt systems is dominated by their redox behavior. It’s became even more complex in the systems where oxo-salts are also redox sensitive, for example in Se and I based systems. In order to better understand the chemistry of An in Se based oxo-systems we performed a series of systematic research on reactivity and phase formation of An bearing selenates and selenites in Th, U and Np systems. Th is good modeling elements for AnIV because it is not redox sensitive and crystal chemically very similar to the UIV, NpIV, and PuIV. Uranium is quite stable in UVI form under ambient atmospheric conditions and can mimic AnVI. Np shows a great diversity in oxidation states and its chemistry is perfectly illustrates complexity of An based systems.
In our study we found that for Th system pH is one of the most important factors for phase formation and their structures. At nearly neutral pH only SeIV phases have been obtained. By changing of pH to the lower range we found very strong hydrolysis with formation of Th based oxo-clusters interlinked by SeVI.
In U based system we found only UVI solid precipitates with different content of SeVI and SeIV which is strongly depends on the initial oxidation of Se.
The Np system is way more complex in comparison to the both previous. We started from an NpV stock solution and surprisingly no NpV solid phases were observed in the precipitate. Two novel one-dimensional Np(IV) selenites were found from reactions of NpV with SeIV: A2[Np(SeO3)2(HSeO3)2]•(H2O) (A=K, Rb). Hereby NpV most likely dispro-portionated into NpIV and NpVI and the lower solubility of NpIV selenites led to a further shift within the equilibrium. Simultaneously novel zero-dimensional NpVI nitrates also formed. The experiments of NpV interacting with SeVI reveal the first NpVI selenates: Cs2[(NpO2)2(SeO4)3], K7[(NpO2)9(SeO4)13.5(H2O)6]•(H2O)20, K2[(NpO2)2(SeO4)3(H2O)2]• (H2O)3.5, and Rb2[(NpO2)2(SeO4)3(H2O)4]•(H2O)3. All of which show two-dimensional layered structures. Such difference in phase formation demonstrates a strong dependence of precipitates chemistry from initial Se valence.
. Langer E.M., Walter O., Colle J.-Y., Bosbach D., Alekseev E.V. (2018) Unexpected behavior of Np in oxo-selenate/oxo-selenite systems. Inorg.Chem. (accepted)
. Xiao B., Langer E., Dellen J., Schlenz H., Bosbach D., Suleimanov E.V., Alekseev E.V. (2015) Chemical and Structural Evolution in the Th-SeO32-/SeO42- system: from simple selenites to cluster based selenate compounds. Inorg.Chem. 54, 3022−3030