MgCo2NiO6 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(2), one O(5), two equivalent O(1), and two equivalent O(6) atoms to form MgO6 octahedra that share  a cornercorner with one Co(2)O6 octahedra,  a cornercorner with one Ni(1)O6 octahedra, corners with four equivalent Co(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-16°. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(6) atoms to form CoO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-11°. In the second Co site, Co(2) is bonded to one O(2), one O(6), two equivalent O(3), and two equivalent O(5) atoms to form CoO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 16°. Ni(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 14°. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), two equivalent Co(1), and one Ni(1) atom to form OMg2Co2Ni square pyramids that share corners with four equivalent O(6)Mg2Co3 square pyramids, edges with two equivalent O(1)Mg2Co2Ni square pyramids, and edges with two equivalent O(6)Mg2Co3 square pyramids. In the second O site, O(2) is bonded in a see-saw-like geometry to one Mg(1), one Co(2), and two equivalent Ni(1) atoms. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Co(1) and two equivalent Co(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Co(1) and two equivalent Ni(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Co(2), and one Ni(1) atom. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one Co(2), and two equivalent Co(1) atoms to form OMg2Co3 square pyramids that share corners with four equivalent O(1)Mg2Co2Ni square pyramids, edges with two equivalent O(1)Mg2Co2Ni square pyramids, and edges with two equivalent O(6)Mg2Co3 square pyramids.
MgCo2NiO6 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(2), one O(5), two equivalent O(1), and two equivalent O(6) atoms to form MgO6 octahedra that share  a cornercorner with one Co(2)O6 octahedra,  a cornercorner with one Ni(1)O6 octahedra, corners with four equivalent Co(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-16°. The Mg(1)-O(2) bond length is 2.12 Å. The Mg(1)-O(5) bond length is 2.10 Å. Both Mg(1)-O(1) bond lengths are 2.11 Å. Both Mg(1)-O(6) bond lengths are 2.09 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(6) atoms to form CoO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-11°. The Co(1)-O(3) bond length is 1.84 Å. The Co(1)-O(4) bond length is 1.99 Å. Both Co(1)-O(1) bond lengths are 2.11 Å. Both Co(1)-O(6) bond lengths are 2.08 Å. In the second Co site, Co(2) is bonded to one O(2), one O(6), two equivalent O(3), and two equivalent O(5) atoms to form CoO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 16°. The Co(2)-O(2) bond length is 1.91 Å. The Co(2)-O(6) bond length is 1.94 Å. Both Co(2)-O(3) bond lengths are 1.91 Å. Both Co(2)-O(5) bond lengths are 1.93 Å. Ni(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(2)O6 octahedra, and edges with two equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles are 14°. The Ni(1)-O(1) bond length is 1.89 Å. The Ni(1)-O(5) bond length is 1.88 Å. Both Ni(1)-O(2) bond lengths are 1.92 Å. Both Ni(1)-O(4) bond lengths are 1.89 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), two equivalent Co(1), and one Ni(1) atom to form OMg2Co2Ni square pyramids that share corners with four equivalent O(6)Mg2Co3 square pyramids, edges with two equivalent O(1)Mg2Co2Ni square pyramids, and edges with two equivalent O(6)Mg2Co3 square pyramids. In the second O site, O(2) is bonded in a see-saw-like geometry to one Mg(1), one Co(2), and two equivalent Ni(1) atoms. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Co(1) and two equivalent Co(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Co(1) and two equivalent Ni(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Co(2), and one Ni(1) atom. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one Co(2), and two equivalent Co(1) atoms to form OMg2Co3 square pyramids that share corners with four equivalent O(1)Mg2Co2Ni square pyramids, edges with two equivalent O(1)Mg2Co2Ni square pyramids, and edges with two equivalent O(6)Mg2Co3 square pyramids.