MgCo4(NiO4)2 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(3) and two equivalent O(4) atoms. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form distorted corner-sharing CoO4 tetrahedra. In the second Co site, Co(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted CoO5 square pyramids that share corners with two equivalent Co(3)O4 tetrahedra, corners with three equivalent Co(1)O4 tetrahedra, and edges with two equivalent Co(2)O5 square pyramids. In the third Co site, Co(3) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form corner-sharing CoO4 tetrahedra. Ni(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Co(1), one Co(2), and two equivalent Ni(1) atoms. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Co(1), two equivalent Co(2), and one Ni(1) atom. In the third O site, O(3) is bonded to one Mg(1), one Co(3), and two equivalent Co(2) atoms to form distorted OMgCo3 tetrahedra that share  a cornercorner with one O(3)MgCo3 tetrahedra, corners with four equivalent O(4)MgCoNi2 tetrahedra, and  a faceface with one O(3)MgCo3 tetrahedra. In the fourth O site, O(4) is bonded to one Mg(1), one Co(3), and two equivalent Ni(1) atoms to form distorted OMgCoNi2 tetrahedra that share  a cornercorner with one O(4)MgCoNi2 tetrahedra, corners with four equivalent O(3)MgCo3 tetrahedra, and  a faceface with one O(4)MgCoNi2 tetrahedra.
MgCo4(NiO4)2 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(3) and two equivalent O(4) atoms. Both Mg(1)-O(3) bond lengths are 2.04 Å. Both Mg(1)-O(4) bond lengths are 2.01 Å. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form distorted corner-sharing CoO4 tetrahedra. Both Co(1)-O(1) bond lengths are 2.07 Å. Both Co(1)-O(2) bond lengths are 2.10 Å. In the second Co site, Co(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted CoO5 square pyramids that share corners with two equivalent Co(3)O4 tetrahedra, corners with three equivalent Co(1)O4 tetrahedra, and edges with two equivalent Co(2)O5 square pyramids. The Co(2)-O(1) bond length is 2.08 Å. Both Co(2)-O(2) bond lengths are 1.99 Å. Both Co(2)-O(3) bond lengths are 2.02 Å. In the third Co site, Co(3) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form corner-sharing CoO4 tetrahedra. Both Co(3)-O(3) bond lengths are 1.92 Å. Both Co(3)-O(4) bond lengths are 1.92 Å. Ni(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(4) atoms. The Ni(1)-O(2) bond length is 2.03 Å. Both Ni(1)-O(1) bond lengths are 1.98 Å. Both Ni(1)-O(4) bond lengths are 2.03 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Co(1), one Co(2), and two equivalent Ni(1) atoms. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Co(1), two equivalent Co(2), and one Ni(1) atom. In the third O site, O(3) is bonded to one Mg(1), one Co(3), and two equivalent Co(2) atoms to form distorted OMgCo3 tetrahedra that share  a cornercorner with one O(3)MgCo3 tetrahedra, corners with four equivalent O(4)MgCoNi2 tetrahedra, and  a faceface with one O(3)MgCo3 tetrahedra. In the fourth O site, O(4) is bonded to one Mg(1), one Co(3), and two equivalent Ni(1) atoms to form distorted OMgCoNi2 tetrahedra that share  a cornercorner with one O(4)MgCoNi2 tetrahedra, corners with four equivalent O(3)MgCo3 tetrahedra, and  a faceface with one O(4)MgCoNi2 tetrahedra.