Mg3Fe3O8 is Spinel-like structured and crystallizes in the trigonal R-3m space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Fe(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2) and three equivalent O(1) atoms to form FeO4 tetrahedra that share corners with three equivalent Fe(2)O6 octahedra and corners with nine equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 57°. In the second Fe site, Fe(2) is bonded to six equivalent O(1) atoms to form FeO6 octahedra that share corners with six equivalent Fe(1)O4 tetrahedra and edges with six equivalent Mg(1)O6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Fe(1), and one Fe(2) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Mg(1) and one Fe(1) atom.
Mg3Fe3O8 is Spinel-like structured and crystallizes in the trigonal R-3m space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Fe(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Mg(1)O6 octahedra. Both Mg(1)-O(2) bond lengths are 2.06 Å. All Mg(1)-O(1) bond lengths are 2.10 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2) and three equivalent O(1) atoms to form FeO4 tetrahedra that share corners with three equivalent Fe(2)O6 octahedra and corners with nine equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 57°. The Fe(1)-O(2) bond length is 1.86 Å. All Fe(1)-O(1) bond lengths are 1.95 Å. In the second Fe site, Fe(2) is bonded to six equivalent O(1) atoms to form FeO6 octahedra that share corners with six equivalent Fe(1)O4 tetrahedra and edges with six equivalent Mg(1)O6 octahedra. All Fe(2)-O(1) bond lengths are 2.02 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Fe(1), and one Fe(2) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Mg(1) and one Fe(1) atom.