U2FeSe5 crystallizes in the monoclinic C2/c space group. U(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. Fe(1) is bonded to two equivalent Se(2) and four equivalent Se(3) atoms to form corner-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles are 40°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to four equivalent U(1) atoms to form SeU4 trigonal pyramids that share corners with eight equivalent Se(3)U3Fe2 trigonal bipyramids, edges with two equivalent Se(3)U3Fe2 trigonal bipyramids, and edges with two equivalent Se(1)U4 trigonal pyramids. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to three equivalent U(1) and one Fe(1) atom. In the third Se site, Se(3) is bonded to three equivalent U(1) and two equivalent Fe(1) atoms to form distorted SeU3Fe2 trigonal bipyramids that share corners with two equivalent Se(3)U3Fe2 trigonal bipyramids, corners with four equivalent Se(1)U4 trigonal pyramids, edges with five equivalent Se(3)U3Fe2 trigonal bipyramids, and  an edgeedge with one Se(1)U4 trigonal pyramid.
U2FeSe5 crystallizes in the monoclinic C2/c space group. U(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. There is one shorter (2.91 Å) and one longer (2.92 Å) U(1)-Se(1) bond length. There are a spread of U(1)-Se(2) bond distances ranging from 2.79-3.20 Å. There is one shorter (2.93 Å) and two longer (2.95 Å) U(1)-Se(3) bond lengths. Fe(1) is bonded to two equivalent Se(2) and four equivalent Se(3) atoms to form corner-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles are 40°. Both Fe(1)-Se(2) bond lengths are 2.61 Å. There are two shorter (2.61 Å) and two longer (2.62 Å) Fe(1)-Se(3) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to four equivalent U(1) atoms to form SeU4 trigonal pyramids that share corners with eight equivalent Se(3)U3Fe2 trigonal bipyramids, edges with two equivalent Se(3)U3Fe2 trigonal bipyramids, and edges with two equivalent Se(1)U4 trigonal pyramids. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to three equivalent U(1) and one Fe(1) atom. In the third Se site, Se(3) is bonded to three equivalent U(1) and two equivalent Fe(1) atoms to form distorted SeU3Fe2 trigonal bipyramids that share corners with two equivalent Se(3)U3Fe2 trigonal bipyramids, corners with four equivalent Se(1)U4 trigonal pyramids, edges with five equivalent Se(3)U3Fe2 trigonal bipyramids, and  an edgeedge with one Se(1)U4 trigonal pyramid.