Li2H2SeO5 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(1), one O(4), and two equivalent O(3) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra, and corners with four equivalent Se(1)O4 tetrahedra. In the second Li site, Li(2) is bonded to one O(2), one O(4), and two equivalent O(5) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(1)O4 tetrahedra, corners with two equivalent Li(2)O4 tetrahedra, and corners with three equivalent Se(1)O4 tetrahedra. There are two inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(2) atom. In the second H site, H(2) is bonded in a single-bond geometry to one O(2) atom. Se(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form SeO4 tetrahedra that share corners with three equivalent Li(2)O4 tetrahedra and corners with four equivalent Li(1)O4 tetrahedra. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Li(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Li(2), one H(1), and one H(2) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to two equivalent Li(1) and one Se(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(1), one Li(2), and one Se(1) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to two equivalent Li(2) and one Se(1) atom.
Li2H2SeO5 crystallizes in the monoclinic P2_1 space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to one O(1), one O(4), and two equivalent O(3) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(2)O4 tetrahedra, corners with two equivalent Li(1)O4 tetrahedra, and corners with four equivalent Se(1)O4 tetrahedra. The Li(1)-O(1) bond length is 1.98 Å. The Li(1)-O(4) bond length is 2.01 Å. There is one shorter (1.98 Å) and one longer (2.05 Å) Li(1)-O(3) bond length. In the second Li site, Li(2) is bonded to one O(2), one O(4), and two equivalent O(5) atoms to form LiO4 tetrahedra that share  a cornercorner with one Li(1)O4 tetrahedra, corners with two equivalent Li(2)O4 tetrahedra, and corners with three equivalent Se(1)O4 tetrahedra. The Li(2)-O(2) bond length is 1.98 Å. The Li(2)-O(4) bond length is 1.97 Å. There is one shorter (2.00 Å) and one longer (2.04 Å) Li(2)-O(5) bond length. There are two inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one O(2) atom. The H(1)-O(2) bond length is 1.00 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(2) atom. The H(2)-O(2) bond length is 0.99 Å. Se(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form SeO4 tetrahedra that share corners with three equivalent Li(2)O4 tetrahedra and corners with four equivalent Li(1)O4 tetrahedra. The Se(1)-O(1) bond length is 1.67 Å. The Se(1)-O(3) bond length is 1.68 Å. The Se(1)-O(4) bond length is 1.68 Å. The Se(1)-O(5) bond length is 1.68 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Li(1) and one Se(1) atom. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Li(2), one H(1), and one H(2) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to two equivalent Li(1) and one Se(1) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Li(1), one Li(2), and one Se(1) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to two equivalent Li(2) and one Se(1) atom.