MgFe4(PO4)4 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with four equivalent P(1)O4 tetrahedra. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted pentagonal planar geometry to one O(5), one O(6), one O(7), and two equivalent O(1) atoms. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), and two equivalent O(8) atoms. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 21-36°. In the second P site, P(2) is bonded to one O(2), one O(4), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 26°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to two equivalent Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a water-like geometry to one Fe(2) and one P(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one P(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one P(2) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to two equivalent Fe(2) and one P(2) atom.
MgFe4(PO4)4 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent P(2)O4 tetrahedra and corners with four equivalent P(1)O4 tetrahedra. Both Mg(1)-O(5) bond lengths are 2.08 Å. Both Mg(1)-O(6) bond lengths are 2.14 Å. Both Mg(1)-O(7) bond lengths are 2.10 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted pentagonal planar geometry to one O(5), one O(6), one O(7), and two equivalent O(1) atoms. The Fe(1)-O(5) bond length is 2.41 Å. The Fe(1)-O(6) bond length is 2.03 Å. The Fe(1)-O(7) bond length is 2.11 Å. There is one shorter (2.02 Å) and one longer (2.10 Å) Fe(1)-O(1) bond length. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), and two equivalent O(8) atoms. The Fe(2)-O(2) bond length is 1.98 Å. The Fe(2)-O(3) bond length is 1.88 Å. The Fe(2)-O(4) bond length is 1.88 Å. There is one shorter (2.02 Å) and one longer (2.17 Å) Fe(2)-O(8) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 21-36°. The P(1)-O(1) bond length is 1.58 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.53 Å. The P(1)-O(6) bond length is 1.55 Å. In the second P site, P(2) is bonded to one O(2), one O(4), one O(7), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 26°. The P(2)-O(2) bond length is 1.55 Å. The P(2)-O(4) bond length is 1.53 Å. The P(2)-O(7) bond length is 1.54 Å. The P(2)-O(8) bond length is 1.58 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to two equivalent Fe(1) and one P(1) atom. In the second O site, O(2) is bonded in a water-like geometry to one Fe(2) and one P(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one P(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one P(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(1), and one P(2) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to two equivalent Fe(2) and one P(2) atom.