NiH2SeO5 crystallizes in the triclinic P-1 space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form NiO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Se(1)O5 trigonal bipyramids, and edges with two equivalent Se(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 27°. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Se(1)O5 trigonal bipyramids, and edges with two equivalent Se(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 27°. 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(3) and one O(5) atom. Se(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(5) atom to form SeO5 trigonal bipyramids that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Ni(2)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra, and  an edgeedge with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles are 33°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Ni(1), one Ni(2), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ni(2), one H(1), and one Se(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Ni(1), one H(2), and one Se(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Ni(2) and one Se(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ni(1), one H(2), and one Se(1) atom.
NiH2SeO5 crystallizes in the triclinic P-1 space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form NiO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Se(1)O5 trigonal bipyramids, and edges with two equivalent Se(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 27°. Both Ni(1)-O(1) bond lengths are 2.05 Å. Both Ni(1)-O(3) bond lengths are 2.05 Å. Both Ni(1)-O(5) bond lengths are 2.13 Å. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Se(1)O5 trigonal bipyramids, and edges with two equivalent Se(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 27°. Both Ni(2)-O(1) bond lengths are 2.05 Å. Both Ni(2)-O(2) bond lengths are 2.05 Å. Both Ni(2)-O(4) bond lengths are 2.12 Å. 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(3) and one O(5) atom. The H(2)-O(3) bond length is 1.00 Å. The H(2)-O(5) bond length is 1.77 Å. Se(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(5) atom to form SeO5 trigonal bipyramids that share  a cornercorner with one Ni(1)O6 octahedra,  a cornercorner with one Ni(2)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra, and  an edgeedge with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles are 33°. The Se(1)-O(1) bond length is 1.75 Å. The Se(1)-O(2) bond length is 1.90 Å. The Se(1)-O(3) bond length is 1.90 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 distorted T-shaped geometry to one Ni(1), one Ni(2), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ni(2), one H(1), and one Se(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one Ni(1), one H(2), and one Se(1) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Ni(2) and one Se(1) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Ni(1), one H(2), and one Se(1) atom.