NaMgFe(SeO4)2 crystallizes in the monoclinic C2 space group. Na(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(2) atoms. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(2) atoms. Fe(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra. 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 three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-58°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Fe(1), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(1), one Mg(1), and one Se(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Na(1), one Fe(1), and one Se(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one Se(1) atom.
NaMgFe(SeO4)2 crystallizes in the monoclinic C2 space group. Na(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(2) atoms. Both Na(1)-O(3) bond lengths are 2.24 Å. There are two shorter (2.57 Å) and two longer (2.89 Å) Na(1)-O(2) bond lengths. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Mg(1)-O(1) bond lengths are 2.03 Å. Both Mg(1)-O(2) bond lengths are 2.11 Å. Fe(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra. Both Fe(1)-O(1) bond lengths are 2.26 Å. Both Fe(1)-O(3) bond lengths are 2.16 Å. Both Fe(1)-O(4) bond lengths are 2.03 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 three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 41-58°. The Se(1)-O(1) bond length is 1.85 Å. The Se(1)-O(2) bond length is 1.75 Å. The Se(1)-O(3) bond length is 1.73 Å. The Se(1)-O(4) bond length is 1.67 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Fe(1), and one Se(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(1), one Mg(1), and one Se(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Na(1), one Fe(1), and one Se(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one Se(1) atom.