USe2O9 crystallizes in the monoclinic C2/c space group. U(1) is bonded to one O(2), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted UO7 pentagonal bipyramids that share corners with four equivalent Se(1)O4 tetrahedra. Se(1) is bonded to one O(3), one O(4), and two equivalent O(5) atoms to form SeO4 tetrahedra that share corners with two equivalent U(1)O7 pentagonal bipyramids and corners with two equivalent Se(1)O4 tetrahedra. There are five inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one U(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one U(1) atom. In the third O site, O(3) is bonded in a linear geometry to one U(1) and one Se(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one U(1) and one Se(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Se(1) atoms.
USe2O9 crystallizes in the monoclinic C2/c space group. U(1) is bonded to one O(2), two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted UO7 pentagonal bipyramids that share corners with four equivalent Se(1)O4 tetrahedra. The U(1)-O(2) bond length is 2.28 Å. Both U(1)-O(1) bond lengths are 1.80 Å. Both U(1)-O(3) bond lengths are 2.42 Å. Both U(1)-O(4) bond lengths are 2.44 Å. Se(1) is bonded to one O(3), one O(4), and two equivalent O(5) atoms to form SeO4 tetrahedra that share corners with two equivalent U(1)O7 pentagonal bipyramids and corners with two equivalent Se(1)O4 tetrahedra. The Se(1)-O(3) bond length is 1.66 Å. The Se(1)-O(4) bond length is 1.68 Å. There is one shorter (1.71 Å) and one longer (2.19 Å) Se(1)-O(5) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one U(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one U(1) atom. In the third O site, O(3) is bonded in a linear geometry to one U(1) and one Se(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one U(1) and one Se(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to two equivalent Se(1) atoms.