Ag ₅ U(PS ₄ ) ₃: A Transition-Metal Actinide Phosphochalcogenide

The structure of Ag ₅ U(PS ₄ ) ₃ is unique, as in the literature there are no other structures of the type MAnPQ (M = transition metal, An = actinide, Q = S, Se, or Te). The compound has been synthesized at 1123 K by standard solid-state methods, and its single-crystal X-ray structure has been determined at 100(2) K. Ag ₅ U(PS ₄ ) ₃ crystallizes in a remarkable new structure type in space group P3 ₂ 21 of the trigonal system with three formula units in a hexagonal cell of dimensions a = b = 9.6635(2) Å, c = 17.1834(4) Å, and γ = 120°. In the structure, each U atom is coordinated to eight S atoms in a bicapped trigonal prismatic manner. Each P atom is tetrahedrally coordinated to four S atoms. Two of the three unique Ag atoms are connected to four S atoms in a distorted tetrahedral manner, whereas the third unique Ag atom forms an Ag ₂ S ₆ species. The overall structure consists of U polyhedra connected to each other via PS ₄ tetrahedra through edge-sharing in a zigzag fashion along the c axis to form infinite layers. PS ₄ groups and the Ag atoms pack these layers. From density functional theory calculations, the total density of states of Ag ₅ U(PS ₄ ) ₃ is asymmetric with respect to spin and has finite spin polarization in the crystal cell: the magnetic moments of two of the U atoms are parallel, whereas the magnetic moment of the third U atom is antiparallel.