MgCo2NiO6 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(3), one O(6), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra, corners with four equivalent Ni(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 10-21°. 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  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 21°. 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 20°. 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 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 are 10°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Co(1) and one Ni(1) atom. In the second O site, O(2) is bonded to two equivalent Mg(1), one Co(2), and two equivalent Ni(1) atoms to form a mixture of corner and edge-sharing OMg2CoNi2 square pyramids. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(1), and two equivalent Co(2) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Co(1), and two equivalent Ni(1) atoms to form a mixture of corner and edge-sharing OMg2CoNi2 square pyramids. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Co(2) and one Ni(1) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(2), and two equivalent Co(1) atoms.
MgCo2NiO6 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(3), one O(6), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra, corners with four equivalent Ni(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 10-21°. The Mg(1)-O(3) bond length is 2.13 Å. The Mg(1)-O(6) bond length is 2.19 Å. There is one shorter (2.06 Å) and one longer (2.13 Å) Mg(1)-O(2) bond length. There is one shorter (2.04 Å) and one longer (2.10 Å) Mg(1)-O(4) bond length. 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  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 21°. The Co(1)-O(3) bond length is 2.05 Å. The Co(1)-O(4) bond length is 2.04 Å. There is one shorter (1.77 Å) and one longer (1.96 Å) Co(1)-O(1) bond length. There is one shorter (1.96 Å) and one longer (1.99 Å) Co(1)-O(6) bond length. 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 20°. The Co(2)-O(2) bond length is 2.01 Å. The Co(2)-O(6) bond length is 2.02 Å. There is one shorter (1.89 Å) and one longer (2.06 Å) Co(2)-O(3) bond length. There is one shorter (1.74 Å) and one longer (2.03 Å) Co(2)-O(5) bond length. 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 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 are 10°. The Ni(1)-O(1) bond length is 2.13 Å. The Ni(1)-O(5) bond length is 2.13 Å. There is one shorter (2.06 Å) and one longer (2.11 Å) Ni(1)-O(2) bond length. There is one shorter (2.05 Å) and one longer (2.10 Å) Ni(1)-O(4) bond length. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Co(1) and one Ni(1) atom. In the second O site, O(2) is bonded to two equivalent Mg(1), one Co(2), and two equivalent Ni(1) atoms to form a mixture of corner and edge-sharing OMg2CoNi2 square pyramids. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(1), and two equivalent Co(2) atoms. In the fourth O site, O(4) is bonded to two equivalent Mg(1), one Co(1), and two equivalent Ni(1) atoms to form a mixture of corner and edge-sharing OMg2CoNi2 square pyramids. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Co(2) and one Ni(1) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(2), and two equivalent Co(1) atoms.