Syntheses and crystal structures of the quaternary uranium lanthanide oxyselenides UYb2O2Se3 and U2Ln2O4Se3 (Ln=Pr, Sm, Gd)

Single crystals of the new uranium lanthanide oxyselenide compounds UYb2O2Se3 and U2Ln2O4Se3 (Ln=Pr, Sm, Gd) have been synthesized from an Sb2Se3 flux. The structures have been determined from single-crystal X-ray diffraction data. UYb2O2Se3 is isostructural to UYb2O2S3. The structure comprises layers of edge-sharing YbSe6 octahedra and double layers of disordered (U/Ln)O4Se4 square antiprisms. The U2Ln2O4Se3 (Ln=Pr, Sm, Gd) compounds are isostructural to U2Ln2O4S3 (Ln=La–Gd) whose structure had been deduced previously from X-ray powder diffraction data. In the structure a dodecahedron of four O atoms and four Se atoms surrounds a site primarily occupied by U and a distorted bicapped octahedron of five Se atoms and three O atoms surrounds a site primarily occupied by the lanthanide. These compounds represent the first examples of quaternary uranium oxyselenides.