MgFe3OF7 crystallizes in the trigonal R3m space group. Mg(1) is bonded to one O(1) and three equivalent F(3) atoms to form MgOF3 tetrahedra that share corners with nine equivalent Fe(1)OF5 octahedra. The corner-sharing octahedral tilt angles range from 54-63°. Fe(1) is bonded to one O(1), one F(1), two equivalent F(2), and two equivalent F(3) atoms to form FeOF5 octahedra that share corners with three equivalent Mg(1)OF3 tetrahedra and edges with four equivalent Fe(1)OF5 octahedra. O(1) is bonded in a tetrahedral geometry to one Mg(1) and three equivalent Fe(1) atoms. There are three inequivalent F sites. In the first F site, F(1) is bonded in a distorted T-shaped geometry to three equivalent Fe(1) atoms. In the second F site, F(2) is bonded in a water-like geometry to two equivalent Fe(1) atoms. In the third F site, F(3) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent Fe(1) atoms.
MgFe3OF7 crystallizes in the trigonal R3m space group. Mg(1) is bonded to one O(1) and three equivalent F(3) atoms to form MgOF3 tetrahedra that share corners with nine equivalent Fe(1)OF5 octahedra. The corner-sharing octahedral tilt angles range from 54-63°. The Mg(1)-O(1) bond length is 1.95 Å. All Mg(1)-F(3) bond lengths are 1.95 Å. Fe(1) is bonded to one O(1), one F(1), two equivalent F(2), and two equivalent F(3) atoms to form FeOF5 octahedra that share corners with three equivalent Mg(1)OF3 tetrahedra and edges with four equivalent Fe(1)OF5 octahedra. The Fe(1)-O(1) bond length is 2.03 Å. The Fe(1)-F(1) bond length is 2.13 Å. Both Fe(1)-F(2) bond lengths are 2.00 Å. Both Fe(1)-F(3) bond lengths are 2.16 Å. O(1) is bonded in a tetrahedral geometry to one Mg(1) and three equivalent Fe(1) atoms. There are three inequivalent F sites. In the first F site, F(1) is bonded in a distorted T-shaped geometry to three equivalent Fe(1) atoms. In the second F site, F(2) is bonded in a water-like geometry to two equivalent Fe(1) atoms. In the third F site, F(3) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent Fe(1) atoms.