MgFe2(CoO4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(4), one O(5), and one O(6) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Co(2)O6 octahedra,  a cornercorner with one Co(1)O5 square pyramid, corners with three equivalent Fe(2)O5 trigonal bipyramids, and  an edgeedge with one Co(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 36-67°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), one O(7), and one O(8) atom. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), one O(5), one O(7), and one O(8) atom to form distorted FeO5 trigonal bipyramids that share corners with three equivalent Co(2)O6 octahedra, corners with two equivalent Co(1)O5 square pyramids, and corners with three equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 48-50°. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(2), one O(3), one O(6), and one O(7) atom to form distorted CoO5 square pyramids that share  a cornercorner with one Mg(1)O5 trigonal bipyramid, corners with two equivalent Fe(2)O5 trigonal bipyramids, edges with two equivalent Co(2)O6 octahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. In the second Co site, Co(2) is bonded to one O(2), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form CoO6 octahedra that share corners with three equivalent Mg(1)O5 trigonal bipyramids, corners with three equivalent Fe(2)O5 trigonal bipyramids, and edges with two equivalent Co(1)O5 square pyramids. There are eight 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 Co(1) atom. In the second O site, O(2) is bonded in a tetrahedral geometry to one Mg(1), one Fe(1), one Co(1), and one Co(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(1), one Co(1), and one Co(2) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Fe(1), and one Fe(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Mg(1), one Fe(2), and one Co(2) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Mg(1), one Co(1), and one Co(2) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Co(1), and one Co(2) atom. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Co(2) atom.
MgFe2(CoO4)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(4), one O(5), and one O(6) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Co(2)O6 octahedra,  a cornercorner with one Co(1)O5 square pyramid, corners with three equivalent Fe(2)O5 trigonal bipyramids, and  an edgeedge with one Co(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 36-67°. The Mg(1)-O(1) bond length is 2.15 Å. The Mg(1)-O(2) bond length is 2.07 Å. The Mg(1)-O(4) bond length is 2.04 Å. The Mg(1)-O(5) bond length is 2.01 Å. The Mg(1)-O(6) bond length is 2.10 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), one O(7), and one O(8) atom. The Fe(1)-O(2) bond length is 1.92 Å. The Fe(1)-O(3) bond length is 1.97 Å. The Fe(1)-O(4) bond length is 1.98 Å. The Fe(1)-O(7) bond length is 2.17 Å. The Fe(1)-O(8) bond length is 1.98 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), one O(5), one O(7), and one O(8) atom to form distorted FeO5 trigonal bipyramids that share corners with three equivalent Co(2)O6 octahedra, corners with two equivalent Co(1)O5 square pyramids, and corners with three equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 48-50°. The Fe(2)-O(1) bond length is 2.07 Å. The Fe(2)-O(4) bond length is 1.94 Å. The Fe(2)-O(5) bond length is 1.94 Å. The Fe(2)-O(7) bond length is 2.10 Å. The Fe(2)-O(8) bond length is 1.96 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(2), one O(3), one O(6), and one O(7) atom to form distorted CoO5 square pyramids that share  a cornercorner with one Mg(1)O5 trigonal bipyramid, corners with two equivalent Fe(2)O5 trigonal bipyramids, edges with two equivalent Co(2)O6 octahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The Co(1)-O(1) bond length is 1.75 Å. The Co(1)-O(2) bond length is 2.02 Å. The Co(1)-O(3) bond length is 1.76 Å. The Co(1)-O(6) bond length is 1.97 Å. The Co(1)-O(7) bond length is 1.96 Å. In the second Co site, Co(2) is bonded to one O(2), one O(3), one O(5), one O(6), one O(7), and one O(8) atom to form CoO6 octahedra that share corners with three equivalent Mg(1)O5 trigonal bipyramids, corners with three equivalent Fe(2)O5 trigonal bipyramids, and edges with two equivalent Co(1)O5 square pyramids. The Co(2)-O(2) bond length is 2.13 Å. The Co(2)-O(3) bond length is 2.18 Å. The Co(2)-O(5) bond length is 1.87 Å. The Co(2)-O(6) bond length is 1.78 Å. The Co(2)-O(7) bond length is 2.01 Å. The Co(2)-O(8) bond length is 1.88 Å. There are eight 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 Co(1) atom. In the second O site, O(2) is bonded in a tetrahedral geometry to one Mg(1), one Fe(1), one Co(1), and one Co(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(1), one Co(1), and one Co(2) atom. In the fourth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Mg(1), one Fe(1), and one Fe(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Mg(1), one Fe(2), and one Co(2) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Mg(1), one Co(1), and one Co(2) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(2), one Co(1), and one Co(2) atom. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Co(2) atom.