MgCo(NiO2)4 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(4), one O(6), and two equivalent O(2) atoms to form distorted MgO4 tetrahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Ni(3)O6 octahedra, and corners with six equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-69°. Co(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form NiO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. In the second Ni site, Ni(2) is bonded in a 5-coordinate geometry to one O(5), two equivalent O(1), and two equivalent O(2) atoms. In the third Ni site, Ni(3) is bonded to one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Co(1), one Ni(1), one Ni(2), and one Ni(3) atom. In the second O site, O(2) is bonded to one Mg(1), one Co(1), one Ni(1), one Ni(2), and one Ni(3) atom to form distorted OMgCoNi3 trigonal bipyramids that share  a cornercorner with one O(4)MgCoNi2 tetrahedra,  a cornercorner with one O(6)MgNi3 tetrahedra,  a cornercorner with one O(5)Ni4 trigonal pyramid,  an edgeedge with one O(4)MgCoNi2 tetrahedra,  an edgeedge with one O(6)MgNi3 tetrahedra, edges with two equivalent O(2)MgCoNi3 trigonal bipyramids, and  an edgeedge with one O(5)Ni4 trigonal pyramid. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Co(1) and two equivalent Ni(1) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Co(1), and two equivalent Ni(1) atoms to form OMgCoNi2 tetrahedra that share  a cornercorner with one O(6)MgNi3 tetrahedra, corners with two equivalent O(2)MgCoNi3 trigonal bipyramids, corners with two equivalent O(5)Ni4 trigonal pyramids,  an edgeedge with one O(6)MgNi3 tetrahedra, and edges with two equivalent O(2)MgCoNi3 trigonal bipyramids. In the fifth O site, O(5) is bonded to one Ni(2), one Ni(3), and two equivalent Ni(1) atoms to form distorted ONi4 trigonal pyramids that share corners with two equivalent O(4)MgCoNi2 tetrahedra, corners with three equivalent O(6)MgNi3 tetrahedra, corners with two equivalent O(2)MgCoNi3 trigonal bipyramids, and edges with two equivalent O(2)MgCoNi3 trigonal bipyramids. In the sixth O site, O(6) is bonded to one Mg(1), one Ni(3), and two equivalent Ni(1) atoms to form distorted OMgNi3 tetrahedra that share  a cornercorner with one O(4)MgCoNi2 tetrahedra, corners with two equivalent O(2)MgCoNi3 trigonal bipyramids, corners with three equivalent O(5)Ni4 trigonal pyramids,  an edgeedge with one O(4)MgCoNi2 tetrahedra, and edges with two equivalent O(2)MgCoNi3 trigonal bipyramids.
MgCo(NiO2)4 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(4), one O(6), and two equivalent O(2) atoms to form distorted MgO4 tetrahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Ni(3)O6 octahedra, and corners with six equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-69°. The Mg(1)-O(4) bond length is 1.95 Å. The Mg(1)-O(6) bond length is 1.99 Å. Both Mg(1)-O(2) bond lengths are 2.02 Å. Co(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The Co(1)-O(3) bond length is 1.86 Å. The Co(1)-O(4) bond length is 1.97 Å. Both Co(1)-O(1) bond lengths are 1.88 Å. Both Co(1)-O(2) bond lengths are 1.92 Å. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form NiO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. The Ni(1)-O(1) bond length is 2.12 Å. The Ni(1)-O(2) bond length is 2.16 Å. The Ni(1)-O(3) bond length is 1.91 Å. The Ni(1)-O(4) bond length is 1.95 Å. The Ni(1)-O(5) bond length is 1.90 Å. The Ni(1)-O(6) bond length is 1.91 Å. In the second Ni site, Ni(2) is bonded in a 5-coordinate geometry to one O(5), two equivalent O(1), and two equivalent O(2) atoms. The Ni(2)-O(5) bond length is 1.95 Å. Both Ni(2)-O(1) bond lengths are 1.92 Å. Both Ni(2)-O(2) bond lengths are 2.27 Å. In the third Ni site, Ni(3) is bonded to one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The Ni(3)-O(5) bond length is 2.09 Å. The Ni(3)-O(6) bond length is 2.07 Å. Both Ni(3)-O(1) bond lengths are 2.08 Å. Both Ni(3)-O(2) bond lengths are 2.13 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Co(1), one Ni(1), one Ni(2), and one Ni(3) atom. In the second O site, O(2) is bonded to one Mg(1), one Co(1), one Ni(1), one Ni(2), and one Ni(3) atom to form distorted OMgCoNi3 trigonal bipyramids that share  a cornercorner with one O(4)MgCoNi2 tetrahedra,  a cornercorner with one O(6)MgNi3 tetrahedra,  a cornercorner with one O(5)Ni4 trigonal pyramid,  an edgeedge with one O(4)MgCoNi2 tetrahedra,  an edgeedge with one O(6)MgNi3 tetrahedra, edges with two equivalent O(2)MgCoNi3 trigonal bipyramids, and  an edgeedge with one O(5)Ni4 trigonal pyramid. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Co(1) and two equivalent Ni(1) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Co(1), and two equivalent Ni(1) atoms to form OMgCoNi2 tetrahedra that share  a cornercorner with one O(6)MgNi3 tetrahedra, corners with two equivalent O(2)MgCoNi3 trigonal bipyramids, corners with two equivalent O(5)Ni4 trigonal pyramids,  an edgeedge with one O(6)MgNi3 tetrahedra, and edges with two equivalent O(2)MgCoNi3 trigonal bipyramids. In the fifth O site, O(5) is bonded to one Ni(2), one Ni(3), and two equivalent Ni(1) atoms to form distorted ONi4 trigonal pyramids that share corners with two equivalent O(4)MgCoNi2 tetrahedra, corners with three equivalent O(6)MgNi3 tetrahedra, corners with two equivalent O(2)MgCoNi3 trigonal bipyramids, and edges with two equivalent O(2)MgCoNi3 trigonal bipyramids. In the sixth O site, O(6) is bonded to one Mg(1), one Ni(3), and two equivalent Ni(1) atoms to form distorted OMgNi3 tetrahedra that share  a cornercorner with one O(4)MgCoNi2 tetrahedra, corners with two equivalent O(2)MgCoNi3 trigonal bipyramids, corners with three equivalent O(5)Ni4 trigonal pyramids,  an edgeedge with one O(4)MgCoNi2 tetrahedra, and edges with two equivalent O(2)MgCoNi3 trigonal bipyramids.