DOE OSTI2020
U2SmSe5 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. there are two inequivalent U+3.50+ sites. In the first U+3.50+ site, U+3.50+ is bonded to seven Se2- atoms to form distorted edge-sharing USe7 pentagonal bipyramids. There are a spread of U–Se bond distances ranging from 2.78–2.99 Å. In the second U+3.50+ site, U+3.50+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of U–Se bond distances ranging from 2.96–3.16 Å. Sm3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Sm–Se bond distances ranging from 2.99–3.16 Å. There are five inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three U+3.50+ and one Sm3+ atom to form distorted SeSmU3 trigonal pyramids that share corners with six SeSm2U3 square pyramids, corners with two equivalent SeSm2U3 trigonal bipyramids, corners with six SeSmU3 trigonal pyramids, edges with three SeSm2U3 square pyramids, edges with two equivalent SeSm2U3 trigonal bipyramids, and an edgeedge with one SeSmU3 trigonal pyramid. In the second Se2- site, Se2- is bonded to three U+3.50+ and one Sm3+ atom to form distorted SeSmU3 trigonal pyramids that share corners with six SeSm2U3 square pyramids, corners with two equivalent SeSm2U3 trigonal bipyramids, corners with six SeSmU3 trigonal pyramids, edges with three SeSm2U3 square pyramids, edges with two equivalent SeSm2U3 trigonal bipyramids, and an edgeedge with one SeSmU3 trigonal pyramid. In the third Se2- site, Se2- is bonded to three U+3.50+ and two equivalent Sm3+ atoms to form SeSm2U3 square pyramids that share corners with four equivalent SeSm2U3 square pyramids, corners with five equivalent SeSm2U3 trigonal bipyramids, corners with eight SeSmU3 trigonal pyramids, edges with three SeSm2U3 square pyramids, edges with two equivalent SeSm2U3 trigonal bipyramids, edges with two SeSmU3 trigonal pyramids, and a faceface with one SeSm2U3 square pyramid. In the fourth Se2- site, Se2- is bonded to three U+3.50+ and two equivalent Sm3+ atoms to form distorted SeSm2U3 trigonal bipyramids that share corners with six SeSm2U3 square pyramids, corners with four equivalent SeSm2U3 trigonal bipyramids, corners with four SeSmU3 trigonal pyramids, edges with six SeSm2U3 square pyramids, and edges with four SeSmU3 trigonal pyramids. In the fifth Se2- site, Se2- is bonded to three U+3.50+ and two equivalent Sm3+ atoms to form distorted SeSm2U3 square pyramids that share corners with eight SeSm2U3 square pyramids, a cornercorner with one SeSm2U3 trigonal bipyramid, corners with four SeSmU3 trigonal pyramids, an edgeedge with one SeSm2U3 square pyramid, edges with four equivalent SeSm2U3 trigonal bipyramids, edges with four SeSmU3 trigonal pyramids, and a faceface with one SeSm2U3 square pyramid.