U12Ir4Se31 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent U sites. In the first U site, U(1) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), two equivalent Se(4), and four equivalent Se(1) atoms. In the second U site, U(2) is bonded in a 8-coordinate geometry to one Se(5), two equivalent Se(3), two equivalent Se(4), and four equivalent Se(1) atoms. Ir(1) is bonded in an octahedral geometry to two equivalent Se(4) and four equivalent Se(1) atoms. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one U(2), two equivalent U(1), and one Ir(1) atom. In the second Se site, Se(2) is bonded in a square co-planar geometry to four equivalent U(1) atoms. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to two equivalent U(1) and two equivalent U(2) atoms. In the fourth Se site, Se(4) is bonded in a rectangular see-saw-like geometry to one U(2), two equivalent U(1), and one Ir(1) atom. In the fifth Se site, Se(5) is bonded in a square co-planar geometry to four equivalent U(2) atoms.
U12Ir4Se31 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent U sites. In the first U site, U(1) is bonded in a 8-coordinate geometry to one Se(2), one Se(3), two equivalent Se(4), and four equivalent Se(1) atoms. The U(1)-Se(2) bond length is 2.86 Å. The U(1)-Se(3) bond length is 2.84 Å. Both U(1)-Se(4) bond lengths are 2.91 Å. There are two shorter (2.90 Å) and two longer (3.01 Å) U(1)-Se(1) bond lengths. In the second U site, U(2) is bonded in a 8-coordinate geometry to one Se(5), two equivalent Se(3), two equivalent Se(4), and four equivalent Se(1) atoms. The U(2)-Se(5) bond length is 3.84 Å. Both U(2)-Se(3) bond lengths are 2.87 Å. Both U(2)-Se(4) bond lengths are 2.92 Å. All U(2)-Se(1) bond lengths are 2.95 Å. Ir(1) is bonded in an octahedral geometry to two equivalent Se(4) and four equivalent Se(1) atoms. Both Ir(1)-Se(4) bond lengths are 2.56 Å. All Ir(1)-Se(1) bond lengths are 2.51 Å. There are five inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one U(2), two equivalent U(1), and one Ir(1) atom. In the second Se site, Se(2) is bonded in a square co-planar geometry to four equivalent U(1) atoms. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to two equivalent U(1) and two equivalent U(2) atoms. In the fourth Se site, Se(4) is bonded in a rectangular see-saw-like geometry to one U(2), two equivalent U(1), and one Ir(1) atom. In the fifth Se site, Se(5) is bonded in a square co-planar geometry to four equivalent U(2) atoms.