BaSe2O5 crystallizes in the monoclinic P2_1/c space group. Ba(1) is bonded in a 9-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and three equivalent O(1) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one O(3), one O(4), and one O(5) atom. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to three equivalent Ba(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one Se(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Se(1) and one Se(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Ba(1) and one Se(2) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one Se(2) atom.
BaSe2O5 crystallizes in the monoclinic P2_1/c space group. Ba(1) is bonded in a 9-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and three equivalent O(1) atoms. There is one shorter (2.88 Å) and one longer (2.95 Å) Ba(1)-O(2) bond length. There is one shorter (2.75 Å) and one longer (2.88 Å) Ba(1)-O(4) bond length. There is one shorter (2.86 Å) and one longer (2.97 Å) Ba(1)-O(5) bond length. There are a spread of Ba(1)-O(1) bond distances ranging from 2.75-2.95 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. The Se(1)-O(1) bond length is 1.68 Å. The Se(1)-O(2) bond length is 1.68 Å. The Se(1)-O(3) bond length is 1.88 Å. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one O(3), one O(4), and one O(5) atom. The Se(2)-O(3) bond length is 1.84 Å. The Se(2)-O(4) bond length is 1.67 Å. The Se(2)-O(5) bond length is 1.67 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to three equivalent Ba(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one Se(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Se(1) and one Se(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Ba(1) and one Se(2) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to two equivalent Ba(1) and one Se(2) atom.