Synthesis and Crystal Structure of Cs 2 U 2 (P 2 Se 9 )(Se 2 ) 2

Black single crystals of Cs 2 U 2 (P 2 Se 9 )(Se 2 ) 2 were synthesized at 1023 K by a solid‐state reaction. Its structure was determined by single‐crystal X‐ray diffraction methods. The compound is isostructural with Rb 2 U 2 (P 2 Se 9 )(Se 2 ) 2 and Cs 2 Th 2 (P 2 Se 9 )(Se 2 ) 2 compounds, and crystallizes in the orthorhombic space group Pbca . Cs 2 U 2 (P 2 Se 9 )(Se 2 ) 2 displays a three‐dimensional structure comprising USe 9 polyhedra connected via the Se 2 2– and P 2 Se 9 species with channels filled by Cs atoms. From electronic structure calculations the compound is found to be a metal with a ferromagnetic arrangement of the magnetic moments.