Synthesis and Characterization of AU₂Se₆ (A = K, Cs)

Two new ternary uranium selenides, AU2Se6 (A = K, Cs), were prepared using the reactive flux method. Single crystal X-ray diffraction was performed on single crystals. The compounds crystallize in the orthorhombic Immm space group, Z = 2. CsU2Se6 has cell parameters of a = 4.046(2) Å, b = 5.559(3) Å, and c = 24.237(12) Å. KU2Se6 has cell parameters of a = 4.058(3) Å, b = 5.556(4) Å, and c = 21.710(17) Å. The compounds are isostructural to the previously reported KTh2Se6. The two-dimensional layered structure is related to ZrSe3 with the alkali metals residing in the interlayer space. The oxidation states of uranium and selenium were evaluated using X-ray photoelectron spectroscopy (XPS). Uranium was found to be tetravalent, while selenium was found to be in two oxidation states, one of which is −2. The other oxidation state is similar to that found in a polyselenide network. While this structure is known, our work examines how the structure changes through the transactinide series.