MgFe3PO7 crystallizes in the triclinic P1 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(7) atom. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent Fe(2)O5 trigonal bipyramids, corners with two equivalent Fe(3)O5 trigonal bipyramids,  an edgeedge with one Fe(2)O5 trigonal bipyramid, and  an edgeedge with one Fe(3)O5 trigonal bipyramid. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent Fe(1)O5 trigonal bipyramids, corners with two equivalent Fe(3)O5 trigonal bipyramids,  an edgeedge with one Fe(1)O5 trigonal bipyramid, and  an edgeedge with one Fe(3)O5 trigonal bipyramid. In the third Fe site, Fe(3) is bonded to one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent Fe(1)O5 trigonal bipyramids, corners with two equivalent Fe(2)O5 trigonal bipyramids,  an edgeedge with one Fe(1)O5 trigonal bipyramid, and  an edgeedge with one Fe(2)O5 trigonal bipyramid. P(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Fe(1)O5 trigonal bipyramids, corners with two equivalent Fe(2)O5 trigonal bipyramids, and corners with two equivalent Fe(3)O5 trigonal bipyramids. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped 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 T-shaped geometry to one Mg(1), one Fe(1), and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(3), and one P(1) atom. In the fourth O site, O(4) is bonded to one Mg(1), one Fe(1), one Fe(2), and one Fe(3) atom to form a mixture of corner and edge-sharing OMgFe3 trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Fe(3), and one P(1) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Fe(1), one Fe(2), and one Fe(3) atom to form a mixture of corner and edge-sharing OMgFe3 trigonal pyramids. In the seventh O site, O(7) is bonded to one Mg(1), one Fe(1), one Fe(2), and one Fe(3) atom to form a mixture of corner and edge-sharing OMgFe3 trigonal pyramids.
MgFe3PO7 crystallizes in the triclinic P1 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(7) atom. The Mg(1)-O(1) bond length is 2.26 Å. The Mg(1)-O(2) bond length is 2.24 Å. The Mg(1)-O(3) bond length is 2.44 Å. The Mg(1)-O(4) bond length is 2.01 Å. The Mg(1)-O(6) bond length is 2.01 Å. The Mg(1)-O(7) 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(4), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent Fe(2)O5 trigonal bipyramids, corners with two equivalent Fe(3)O5 trigonal bipyramids,  an edgeedge with one Fe(2)O5 trigonal bipyramid, and  an edgeedge with one Fe(3)O5 trigonal bipyramid. The Fe(1)-O(2) bond length is 2.24 Å. The Fe(1)-O(4) bond length is 2.12 Å. The Fe(1)-O(5) bond length is 2.33 Å. The Fe(1)-O(6) bond length is 2.00 Å. The Fe(1)-O(7) bond length is 2.11 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent Fe(1)O5 trigonal bipyramids, corners with two equivalent Fe(3)O5 trigonal bipyramids,  an edgeedge with one Fe(1)O5 trigonal bipyramid, and  an edgeedge with one Fe(3)O5 trigonal bipyramid. The Fe(2)-O(1) bond length is 2.22 Å. The Fe(2)-O(4) bond length is 2.00 Å. The Fe(2)-O(5) bond length is 2.35 Å. The Fe(2)-O(6) bond length is 2.13 Å. The Fe(2)-O(7) bond length is 2.10 Å. In the third Fe site, Fe(3) is bonded to one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form FeO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with two equivalent Fe(1)O5 trigonal bipyramids, corners with two equivalent Fe(2)O5 trigonal bipyramids,  an edgeedge with one Fe(1)O5 trigonal bipyramid, and  an edgeedge with one Fe(2)O5 trigonal bipyramid. The Fe(3)-O(3) bond length is 2.01 Å. The Fe(3)-O(4) bond length is 1.96 Å. The Fe(3)-O(5) bond length is 2.19 Å. The Fe(3)-O(6) bond length is 1.96 Å. The Fe(3)-O(7) bond length is 1.92 Å. P(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form PO4 tetrahedra that share corners with two equivalent Fe(1)O5 trigonal bipyramids, corners with two equivalent Fe(2)O5 trigonal bipyramids, and corners with two equivalent Fe(3)O5 trigonal bipyramids. The P(1)-O(1) bond length is 1.55 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(5) bond length is 1.56 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped 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 T-shaped geometry to one Mg(1), one Fe(1), and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Fe(3), and one P(1) atom. In the fourth O site, O(4) is bonded to one Mg(1), one Fe(1), one Fe(2), and one Fe(3) atom to form a mixture of corner and edge-sharing OMgFe3 trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Fe(3), and one P(1) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Fe(1), one Fe(2), and one Fe(3) atom to form a mixture of corner and edge-sharing OMgFe3 trigonal pyramids. In the seventh O site, O(7) is bonded to one Mg(1), one Fe(1), one Fe(2), and one Fe(3) atom to form a mixture of corner and edge-sharing OMgFe3 trigonal pyramids.