Syntheses and crystal structures of three barium uranium sulfides

The barium uranium sulfides Ba_3.69US₆, BaUS ₃, and BaU₂S₅ have been synthesized at 1273, 1323, and 1323 K, respectively. The structures of these compounds have been determined by single-crystal X-ray diffraction methods. They crystallize in space groups D3d6-R3̄c, D2h16-Pnma, and C2h5-P2₁/c, respectively. Among these three ternaries and Ba₂US₆ the coordination geometries about the U atoms vary considerably. Ba _3.69US₆ is a mixed U⁴⁺/U⁵⁺compound whereas the others are U⁴⁺ compounds. The decreasing dimensionality of the four compounds with increasing Ba-to-U content shows the expected trend.