FeSeO4 crystallizes in the orthorhombic Cmcm space group. Fe(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra and edges with two equivalent Fe(1)O6 octahedra. Se(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form SeO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-54°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one Se(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Fe(1) and one Se(1) atom.
FeSeO4 crystallizes in the orthorhombic Cmcm space group. Fe(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra and edges with two equivalent Fe(1)O6 octahedra. Both Fe(1)-O(2) bond lengths are 2.07 Å. All Fe(1)-O(1) bond lengths are 2.22 Å. Se(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form SeO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-54°. Both Se(1)-O(1) bond lengths are 1.70 Å. Both Se(1)-O(2) bond lengths are 1.66 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to two equivalent Fe(1) and one Se(1) atom. In the second O site, O(2) is bonded in a bent 120 degrees geometry to one Fe(1) and one Se(1) atom.