UFeSe3 crystallizes in the orthorhombic Cmcm space group. U(1) is bonded in a 8-coordinate geometry to two equivalent Se(2) and six equivalent Se(1) atoms. Fe(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent U(1) and two equivalent Fe(1) atoms to form distorted SeU3Fe2 trigonal bipyramids that share corners with four equivalent Se(2)U2Fe2 tetrahedra, corners with nine equivalent Se(1)U3Fe2 trigonal bipyramids, edges with three equivalent Se(2)U2Fe2 tetrahedra, and edges with six equivalent Se(1)U3Fe2 trigonal bipyramids. In the second Se site, Se(2) is bonded to two equivalent U(1) and two equivalent Fe(1) atoms to form distorted SeU2Fe2 tetrahedra that share corners with four equivalent Se(2)U2Fe2 tetrahedra, corners with eight equivalent Se(1)U3Fe2 trigonal bipyramids, and edges with six equivalent Se(1)U3Fe2 trigonal bipyramids.
UFeSe3 crystallizes in the orthorhombic Cmcm space group. U(1) is bonded in a 8-coordinate geometry to two equivalent Se(2) and six equivalent Se(1) atoms. Both U(1)-Se(2) bond lengths are 2.86 Å. There are four shorter (2.90 Å) and two longer (3.14 Å) U(1)-Se(1) bond lengths. Fe(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form a mixture of corner and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles are 46°. Both Fe(1)-Se(2) bond lengths are 2.50 Å. All Fe(1)-Se(1) bond lengths are 2.63 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent U(1) and two equivalent Fe(1) atoms to form distorted SeU3Fe2 trigonal bipyramids that share corners with four equivalent Se(2)U2Fe2 tetrahedra, corners with nine equivalent Se(1)U3Fe2 trigonal bipyramids, edges with three equivalent Se(2)U2Fe2 tetrahedra, and edges with six equivalent Se(1)U3Fe2 trigonal bipyramids. In the second Se site, Se(2) is bonded to two equivalent U(1) and two equivalent Fe(1) atoms to form distorted SeU2Fe2 tetrahedra that share corners with four equivalent Se(2)U2Fe2 tetrahedra, corners with eight equivalent Se(1)U3Fe2 trigonal bipyramids, and edges with six equivalent Se(1)U3Fe2 trigonal bipyramids.