Synthetic Strategies for the Synthesis of Ternary Uranium(IV) and Thorium(IV) Fluorides.

A series of new U(IV) and Th(IV) fluorides, NaUF (1), NaUF (2), NaUF (3), KThF (4), NaThF (5), (HO)ThF (6), and (HO)UF (7), was obtained using hydrothermal and low-temperature flux methods. Mild hydrothermal reactions with uranyl acetate as a precursor yielded 1, 7, and the monoclinic polymorph of NaUF, whereas direct reactions between UF and NaF led to the formation of 2 and orthorhombic NaUF (3). This highlights an unexpected difference in reaction products when different starting uranium sources are used. All seven compounds were characterized by single-crystal X-ray diffraction, and their structures are compared on the basis of cation topology, revealing a close topological resemblance between fluorides on the basis of the layers observed in NaUF(HO). Phase-pure samples of 1, 2, and both polymorphs of NaUF were obtained, and their spectroscopic and magnetic properties were measured. The UV-vis data are dominated by the presence of U cations and agree well with the electronic transitions. Effective magnetic moments of the studied compounds were found to range from 3.08 to 3.59 μ.