MgFe2(PO4)2 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(8) atom. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form distorted FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  a cornercorner with one Fe(3)O4 trigonal pyramid. In the second Fe site, Fe(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. In the third Fe site, Fe(3) is bonded to two equivalent O(5) and two equivalent O(7) atoms to form distorted FeO4 trigonal pyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and corners with two equivalent Fe(1)O5 trigonal bipyramids. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(4), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Fe(1)O5 trigonal bipyramids and  a cornercorner with one Fe(3)O4 trigonal pyramid. In the second P site, P(2) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O5 trigonal bipyramids and  a cornercorner with one Fe(3)O4 trigonal pyramid. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(2), and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one P(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one P(2) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(1), one Fe(2), and one P(1) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Fe(3) and one P(2) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Mg(1), one Fe(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(3), and one P(1) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Mg(1) and one P(1) atom.
MgFe2(PO4)2 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(8) atom. The Mg(1)-O(1) bond length is 2.16 Å. The Mg(1)-O(2) bond length is 2.12 Å. The Mg(1)-O(3) bond length is 2.37 Å. The Mg(1)-O(4) bond length is 2.36 Å. The Mg(1)-O(6) bond length is 2.12 Å. The Mg(1)-O(8) bond length is 2.01 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), one O(4), one O(6), and one O(7) atom to form distorted FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and  a cornercorner with one Fe(3)O4 trigonal pyramid. The Fe(1)-O(2) bond length is 2.02 Å. The Fe(1)-O(3) bond length is 2.21 Å. The Fe(1)-O(4) bond length is 2.21 Å. The Fe(1)-O(6) bond length is 2.12 Å. The Fe(1)-O(7) bond length is 2.06 Å. In the second Fe site, Fe(2) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. Both Fe(2)-O(1) bond lengths are 2.07 Å. Both Fe(2)-O(3) bond lengths are 2.60 Å. Both Fe(2)-O(4) bond lengths are 2.10 Å. In the third Fe site, Fe(3) is bonded to two equivalent O(5) and two equivalent O(7) atoms to form distorted FeO4 trigonal pyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent P(2)O4 tetrahedra, and corners with two equivalent Fe(1)O5 trigonal bipyramids. Both Fe(3)-O(5) bond lengths are 1.99 Å. Both Fe(3)-O(7) bond lengths are 2.05 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(4), one O(7), and one O(8) atom to form PO4 tetrahedra that share corners with two equivalent Fe(1)O5 trigonal bipyramids and  a cornercorner with one Fe(3)O4 trigonal pyramid. The P(1)-O(1) bond length is 1.57 Å. The P(1)-O(4) bond length is 1.58 Å. The P(1)-O(7) bond length is 1.58 Å. The P(1)-O(8) bond length is 1.50 Å. In the second P site, P(2) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Fe(1)O5 trigonal bipyramids and  a cornercorner with one Fe(3)O4 trigonal pyramid. The P(2)-O(2) bond length is 1.56 Å. The P(2)-O(3) bond length is 1.58 Å. The P(2)-O(5) bond length is 1.52 Å. The P(2)-O(6) bond length is 1.57 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(2), and one P(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Fe(1), and one P(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one P(2) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Fe(1), one Fe(2), and one P(1) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Fe(3) and one P(2) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Mg(1), one Fe(1), and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(3), and one P(1) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Mg(1) and one P(1) atom.