MgZn2(FeO2)4 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra and edges with four equivalent Fe(2)O6 octahedra. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(2), two equivalent O(1), and three equivalent O(3) atoms. In the second Fe site, Fe(2) is bonded to one O(1), two equivalent O(2), and three equivalent O(4) atoms to form distorted FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra and edges with four equivalent Fe(2)O6 octahedra. Zn(1) is bonded in a distorted see-saw-like geometry to one O(1), one O(4), and two equivalent O(3) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Mg(1), one Fe(2), two equivalent Fe(1), and one Zn(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms to form OMgFe3 trigonal pyramids that share corners with three equivalent O(3)Zn2Fe3 square pyramids, corners with three equivalent O(2)MgFe3 trigonal pyramids, corners with four equivalent O(4)ZnFe3 trigonal pyramids, and  an edgeedge with one O(4)ZnFe3 trigonal pyramid. In the third O site, O(3) is bonded to three equivalent Fe(1) and two equivalent Zn(1) atoms to form OZn2Fe3 square pyramids that share corners with two equivalent O(4)ZnFe3 trigonal pyramids, corners with three equivalent O(2)MgFe3 trigonal pyramids, and edges with four equivalent O(3)Zn2Fe3 square pyramids. In the fourth O site, O(4) is bonded to three equivalent Fe(2) and one Zn(1) atom to form OZnFe3 trigonal pyramids that share corners with two equivalent O(3)Zn2Fe3 square pyramids, corners with two equivalent O(4)ZnFe3 trigonal pyramids, corners with four equivalent O(2)MgFe3 trigonal pyramids,  an edgeedge with one O(2)MgFe3 trigonal pyramid, and edges with two equivalent O(4)ZnFe3 trigonal pyramids.
MgZn2(FeO2)4 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra and edges with four equivalent Fe(2)O6 octahedra. Both Mg(1)-O(2) bond lengths are 2.07 Å. There are two shorter (2.07 Å) and two longer (2.15 Å) Mg(1)-O(1) bond lengths. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one O(2), two equivalent O(1), and three equivalent O(3) atoms. The Fe(1)-O(2) bond length is 2.17 Å. There is one shorter (2.10 Å) and one longer (2.62 Å) Fe(1)-O(1) bond length. There are a spread of Fe(1)-O(3) bond distances ranging from 2.05-2.41 Å. In the second Fe site, Fe(2) is bonded to one O(1), two equivalent O(2), and three equivalent O(4) atoms to form distorted FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra and edges with four equivalent Fe(2)O6 octahedra. The Fe(2)-O(1) bond length is 2.29 Å. There is one shorter (1.95 Å) and one longer (1.99 Å) Fe(2)-O(2) bond length. There are a spread of Fe(2)-O(4) bond distances ranging from 1.99-2.18 Å. Zn(1) is bonded in a distorted see-saw-like geometry to one O(1), one O(4), and two equivalent O(3) atoms. The Zn(1)-O(1) bond length is 2.10 Å. The Zn(1)-O(4) bond length is 1.97 Å. There is one shorter (2.00 Å) and one longer (2.04 Å) Zn(1)-O(3) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Mg(1), one Fe(2), two equivalent Fe(1), and one Zn(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms to form OMgFe3 trigonal pyramids that share corners with three equivalent O(3)Zn2Fe3 square pyramids, corners with three equivalent O(2)MgFe3 trigonal pyramids, corners with four equivalent O(4)ZnFe3 trigonal pyramids, and  an edgeedge with one O(4)ZnFe3 trigonal pyramid. In the third O site, O(3) is bonded to three equivalent Fe(1) and two equivalent Zn(1) atoms to form OZn2Fe3 square pyramids that share corners with two equivalent O(4)ZnFe3 trigonal pyramids, corners with three equivalent O(2)MgFe3 trigonal pyramids, and edges with four equivalent O(3)Zn2Fe3 square pyramids. In the fourth O site, O(4) is bonded to three equivalent Fe(2) and one Zn(1) atom to form OZnFe3 trigonal pyramids that share corners with two equivalent O(3)Zn2Fe3 square pyramids, corners with two equivalent O(4)ZnFe3 trigonal pyramids, corners with four equivalent O(2)MgFe3 trigonal pyramids,  an edgeedge with one O(2)MgFe3 trigonal pyramid, and edges with two equivalent O(4)ZnFe3 trigonal pyramids.