Secondary Role of Aliphatic and Heterocyclic Amines in the Formation of Low-Temperature Amine-Bearing U, Np, and Pu(VI) Chromates

Uranyl compounds with tetrahedral oxoanions demonstrate a significant structural and topological diversity. Complexes of transuranium elements with such anions are not equally well-represented in the literature. To answer the question about the structural similarity in a series of An⁶⁺ complexes with XO₄^2- anions, we synthesized and studied 10 new U, Np, and Pu chromates with outer-sphere organic cations. The structural analysis and comparison with the literature data shows that the Np and Pu complexes are generally based on the same structural blocks as the uranyl compounds. Moreover, the chromate anion does not show any unique structural role as compared to the sulfate and selenate ions. As a result, the neptunium and plutonium chromates contain 1D and 2D structural units similar to those found in the uranyl sulfates and selenates. The templating role of the outer-sphere cations in the actinyl complexes with tetrahedral oxoanions is also not evident, and there is no clear correlation between the nature of the outer-sphere cations and the topology of the structural units.