U3O8 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent U sites. In the first U site, U(1) is bonded to one O(2), two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form UO7 pentagonal bipyramids that share corners with two equivalent U(2)O6 octahedra, corners with three equivalent U(1)O7 pentagonal bipyramids,  an edgeedge with one U(2)O6 octahedra, and edges with two equivalent U(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 37-46°. In the second U site, U(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form UO6 octahedra that share corners with two equivalent U(2)O6 octahedra, corners with four equivalent U(1)O7 pentagonal bipyramids, and edges with two equivalent U(1)O7 pentagonal bipyramids. The corner-sharing octahedra are not tilted. There are five inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent U(1) atoms. In the second O site, O(2) is bonded in a linear geometry to two equivalent U(1) atoms. In the third O site, O(3) is bonded in a linear geometry to two equivalent U(2) atoms. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one U(2) and two equivalent U(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one U(2) and two equivalent U(1) atoms.
U3O8 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent U sites. In the first U site, U(1) is bonded to one O(2), two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form UO7 pentagonal bipyramids that share corners with two equivalent U(2)O6 octahedra, corners with three equivalent U(1)O7 pentagonal bipyramids,  an edgeedge with one U(2)O6 octahedra, and edges with two equivalent U(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 37-46°. The U(1)-O(2) bond length is 2.08 Å. Both U(1)-O(1) bond lengths are 2.07 Å. There is one shorter (2.31 Å) and one longer (2.32 Å) U(1)-O(4) bond length. There is one shorter (2.26 Å) and one longer (2.46 Å) U(1)-O(5) bond length. In the second U site, U(2) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form UO6 octahedra that share corners with two equivalent U(2)O6 octahedra, corners with four equivalent U(1)O7 pentagonal bipyramids, and edges with two equivalent U(1)O7 pentagonal bipyramids. The corner-sharing octahedra are not tilted. Both U(2)-O(3) bond lengths are 2.07 Å. Both U(2)-O(4) bond lengths are 2.10 Å. Both U(2)-O(5) bond lengths are 2.08 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent U(1) atoms. In the second O site, O(2) is bonded in a linear geometry to two equivalent U(1) atoms. In the third O site, O(3) is bonded in a linear geometry to two equivalent U(2) atoms. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one U(2) and two equivalent U(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one U(2) and two equivalent U(1) atoms.