U3O8 crystallizes in the orthorhombic Cmcm space group. There are three inequivalent U sites. In the first U site, U(1) is bonded to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form UO7 pentagonal bipyramids that share corners with four equivalent U(3)O6 octahedra,  a cornercorner with one U(2)O7 pentagonal bipyramid,  an edgeedge with one U(3)O6 octahedra, and edges with two equivalent U(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 4-41°. In the second U site, U(2) is bonded to one O(4), two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form UO7 pentagonal bipyramids that share corners with two equivalent U(3)O6 octahedra,  a cornercorner with one U(1)O7 pentagonal bipyramid, corners with two equivalent U(2)O7 pentagonal bipyramids,  an edgeedge with one U(3)O6 octahedra, and edges with two equivalent U(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. In the third U site, U(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form a mixture of edge and corner-sharing UO6 octahedra. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one U(1), one U(2), and one U(3) atom. In the second O site, O(2) is bonded in a linear geometry to one U(1) and one U(3) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one U(1), one U(2), and one U(3) atom. In the fourth O site, O(4) is bonded in a linear geometry to one U(1) and one U(2) atom. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent U(2) atoms.
U3O8 crystallizes in the orthorhombic Cmcm space group. There are three inequivalent U sites. In the first U site, U(1) is bonded to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form UO7 pentagonal bipyramids that share corners with four equivalent U(3)O6 octahedra,  a cornercorner with one U(2)O7 pentagonal bipyramid,  an edgeedge with one U(3)O6 octahedra, and edges with two equivalent U(2)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 4-41°. The U(1)-O(4) bond length is 2.06 Å. Both U(1)-O(1) bond lengths are 2.27 Å. Both U(1)-O(2) bond lengths are 1.93 Å. Both U(1)-O(3) bond lengths are 2.36 Å. In the second U site, U(2) is bonded to one O(4), two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form UO7 pentagonal bipyramids that share corners with two equivalent U(3)O6 octahedra,  a cornercorner with one U(1)O7 pentagonal bipyramid, corners with two equivalent U(2)O7 pentagonal bipyramids,  an edgeedge with one U(3)O6 octahedra, and edges with two equivalent U(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. The U(2)-O(4) bond length is 2.09 Å. Both U(2)-O(1) bond lengths are 2.41 Å. Both U(2)-O(3) bond lengths are 2.26 Å. Both U(2)-O(5) bond lengths are 2.08 Å. In the third U site, U(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form a mixture of edge and corner-sharing UO6 octahedra. Both U(3)-O(1) bond lengths are 2.10 Å. Both U(3)-O(2) bond lengths are 2.23 Å. Both U(3)-O(3) bond lengths are 2.12 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one U(1), one U(2), and one U(3) atom. In the second O site, O(2) is bonded in a linear geometry to one U(1) and one U(3) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one U(1), one U(2), and one U(3) atom. In the fourth O site, O(4) is bonded in a linear geometry to one U(1) and one U(2) atom. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent U(2) atoms.