NaHSeO4 crystallizes in the monoclinic P2_1/c space group. Na(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with six equivalent Se(1)O4 tetrahedra, and  an edgeedge with one Na(1)O6 octahedra. The corner-sharing octahedral tilt angles are 67°. H(1) is bonded in a single-bond geometry to one O(3) and one O(4) atom. Se(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SeO4 tetrahedra that share corners with six equivalent Na(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 32-65°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Na(1) and one Se(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to two equivalent Na(1) and one Se(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one H(1), and one Se(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1), one H(1), and one Se(1) atom.
NaHSeO4 crystallizes in the monoclinic P2_1/c space group. Na(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with six equivalent Se(1)O4 tetrahedra, and  an edgeedge with one Na(1)O6 octahedra. The corner-sharing octahedral tilt angles are 67°. The Na(1)-O(3) bond length is 2.48 Å. The Na(1)-O(4) bond length is 2.49 Å. There is one shorter (2.39 Å) and one longer (2.42 Å) Na(1)-O(1) bond length. There is one shorter (2.44 Å) and one longer (2.45 Å) Na(1)-O(2) bond length. H(1) is bonded in a single-bond geometry to one O(3) and one O(4) atom. The H(1)-O(3) bond length is 1.74 Å. The H(1)-O(4) bond length is 1.02 Å. Se(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SeO4 tetrahedra that share corners with six equivalent Na(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 32-65°. The Se(1)-O(1) bond length is 1.64 Å. The Se(1)-O(2) bond length is 1.65 Å. The Se(1)-O(3) bond length is 1.66 Å. The Se(1)-O(4) bond length is 1.78 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Na(1) and one Se(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to two equivalent Na(1) and one Se(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one H(1), and one Se(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1), one H(1), and one Se(1) atom.