Mg4FeO13Cl crystallizes in the monoclinic C2 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form edge-sharing MgO6 octahedra. In the third Mg site, Mg(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form distorted edge-sharing MgO6 octahedra. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Fe(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Mg(3), one Fe(1), and one O(6) atom to form distorted OMg2FeO trigonal pyramids that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(1)Mg2FeO trigonal pyramid, and  an edgeedge with one O(2)Mg2FeO trigonal pyramid. In the second O site, O(2) is bonded to one Mg(3), one Mg(4), one Fe(1), and one O(7) atom to form OMg2FeO trigonal pyramids that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(3)Mg2FeCl tetrahedra,  an edgeedge with one O(1)Mg2FeO trigonal pyramid, and  an edgeedge with one O(2)Mg2FeO trigonal pyramid. In the third O site, O(3) is bonded to one Mg(1), one Mg(4), one Fe(1), and one Cl(1) atom to form distorted OMg2FeCl tetrahedra that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(3)Mg2FeCl tetrahedra,  an edgeedge with one O(2)Mg2FeO trigonal pyramid, and  an edgeedge with one O(4)Mg3O trigonal pyramid. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), one Mg(4), and one O(8) atom to form distorted OMg3O trigonal pyramids that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(3)Mg2FeCl tetrahedra, and  an edgeedge with one O(4)Mg3O trigonal pyramid. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Mg(2), and one Mg(3) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to two equivalent O(1) atoms. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to two equivalent O(2) atoms. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to two equivalent O(4) atoms. Cl(1) is bonded in a linear geometry to two equivalent O(3) atoms.
Mg4FeO13Cl crystallizes in the monoclinic C2 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. Both Mg(1)-O(3) bond lengths are 2.10 Å. Both Mg(1)-O(4) bond lengths are 2.42 Å. Both Mg(1)-O(5) bond lengths are 2.00 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form edge-sharing MgO6 octahedra. Both Mg(2)-O(1) bond lengths are 2.24 Å. Both Mg(2)-O(4) bond lengths are 2.16 Å. Both Mg(2)-O(5) bond lengths are 2.02 Å. In the third Mg site, Mg(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form distorted edge-sharing MgO6 octahedra. Both Mg(3)-O(1) bond lengths are 2.29 Å. Both Mg(3)-O(2) bond lengths are 2.18 Å. Both Mg(3)-O(5) bond lengths are 1.99 Å. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Both Mg(4)-O(2) bond lengths are 2.26 Å. Both Mg(4)-O(3) bond lengths are 1.90 Å. Both Mg(4)-O(4) bond lengths are 2.66 Å. Fe(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. Both Fe(1)-O(1) bond lengths are 2.13 Å. Both Fe(1)-O(2) bond lengths are 2.24 Å. Both Fe(1)-O(3) bond lengths are 2.03 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Mg(3), one Fe(1), and one O(6) atom to form distorted OMg2FeO trigonal pyramids that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(1)Mg2FeO trigonal pyramid, and  an edgeedge with one O(2)Mg2FeO trigonal pyramid. The O(1)-O(6) bond length is 1.50 Å. In the second O site, O(2) is bonded to one Mg(3), one Mg(4), one Fe(1), and one O(7) atom to form OMg2FeO trigonal pyramids that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(3)Mg2FeCl tetrahedra,  an edgeedge with one O(1)Mg2FeO trigonal pyramid, and  an edgeedge with one O(2)Mg2FeO trigonal pyramid. The O(2)-O(7) bond length is 1.48 Å. In the third O site, O(3) is bonded to one Mg(1), one Mg(4), one Fe(1), and one Cl(1) atom to form distorted OMg2FeCl tetrahedra that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(3)Mg2FeCl tetrahedra,  an edgeedge with one O(2)Mg2FeO trigonal pyramid, and  an edgeedge with one O(4)Mg3O trigonal pyramid. The O(3)-Cl(1) bond length is 1.90 Å. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), one Mg(4), and one O(8) atom to form distorted OMg3O trigonal pyramids that share corners with two equivalent O(3)Mg2FeCl tetrahedra, corners with two equivalent O(1)Mg2FeO trigonal pyramids, corners with two equivalent O(2)Mg2FeO trigonal pyramids, corners with two equivalent O(4)Mg3O trigonal pyramids,  an edgeedge with one O(3)Mg2FeCl tetrahedra, and  an edgeedge with one O(4)Mg3O trigonal pyramid. The O(4)-O(8) bond length is 1.37 Å. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Mg(2), and one Mg(3) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to two equivalent O(1) atoms. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to two equivalent O(2) atoms. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to two equivalent O(4) atoms. Cl(1) is bonded in a linear geometry to two equivalent O(3) atoms.