Ba2U2O7 crystallizes in the orthorhombic Imma space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent O(1), two equivalent O(3), and four equivalent O(2) atoms to form distorted BaO8 hexagonal bipyramids that share corners with two equivalent Ba(1)O8 hexagonal bipyramids, corners with two equivalent U(2)O6 octahedra, edges with two equivalent U(2)O6 octahedra, and edges with four equivalent U(1)O6 octahedra. The corner-sharing octahedral tilt angles are 55°. In the second Ba site, Ba(2) is bonded in a distorted body-centered cubic geometry to four equivalent O(2) and four equivalent O(3) atoms. There are two inequivalent U sites. In the first U site, U(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form UO6 octahedra that share corners with two equivalent U(1)O6 octahedra, corners with four equivalent U(2)O6 octahedra, and edges with four equivalent Ba(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 40-43°. In the second U site, U(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form UO6 octahedra that share corners with two equivalent Ba(1)O8 hexagonal bipyramids, corners with four equivalent U(1)O6 octahedra, and edges with two equivalent Ba(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1) and two equivalent U(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one U(1), and one U(2) atom. In the third O site, O(3) is bonded to one Ba(1), two equivalent Ba(2), and one U(2) atom to form a mixture of distorted edge and corner-sharing OBa3U tetrahedra.
Ba2U2O7 crystallizes in the orthorhombic Imma space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent O(1), two equivalent O(3), and four equivalent O(2) atoms to form distorted BaO8 hexagonal bipyramids that share corners with two equivalent Ba(1)O8 hexagonal bipyramids, corners with two equivalent U(2)O6 octahedra, edges with two equivalent U(2)O6 octahedra, and edges with four equivalent U(1)O6 octahedra. The corner-sharing octahedral tilt angles are 55°. Both Ba(1)-O(1) bond lengths are 3.13 Å. Both Ba(1)-O(3) bond lengths are 2.58 Å. All Ba(1)-O(2) bond lengths are 2.83 Å. In the second Ba site, Ba(2) is bonded in a distorted body-centered cubic geometry to four equivalent O(2) and four equivalent O(3) atoms. All Ba(2)-O(2) bond lengths are 3.04 Å. All Ba(2)-O(3) bond lengths are 2.73 Å. There are two inequivalent U sites. In the first U site, U(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form UO6 octahedra that share corners with two equivalent U(1)O6 octahedra, corners with four equivalent U(2)O6 octahedra, and edges with four equivalent Ba(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 40-43°. Both U(1)-O(1) bond lengths are 2.18 Å. All U(1)-O(2) bond lengths are 2.14 Å. In the second U site, U(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form UO6 octahedra that share corners with two equivalent Ba(1)O8 hexagonal bipyramids, corners with four equivalent U(1)O6 octahedra, and edges with two equivalent Ba(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 43°. Both U(2)-O(3) bond lengths are 2.06 Å. All U(2)-O(2) bond lengths are 2.22 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1) and two equivalent U(1) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one U(1), and one U(2) atom. In the third O site, O(3) is bonded to one Ba(1), two equivalent Ba(2), and one U(2) atom to form a mixture of distorted edge and corner-sharing OBa3U tetrahedra.