Li2MgNi3O8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form LiO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Li(2)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 12-13°. In the second Li site, Li(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form LiO6 octahedra that share corners with six equivalent Ni(2)O6 octahedra, edges with two equivalent Li(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-12°. Mg(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Li(1)O6 octahedra, edges with two equivalent Li(2)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 12-13°. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share edges with two equivalent Li(1)O6 octahedra, edges with two equivalent Li(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(2)O6 octahedra. In the second Ni site, Ni(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Li(2)O6 octahedra, edges with two equivalent Li(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-12°. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Li(1), one Li(2), one Mg(1), one Ni(1), and one Ni(2) atom to form a mixture of edge and corner-sharing OLi2MgNi2 square pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Li(2), one Ni(2), and two equivalent Ni(1) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Li(1), one Mg(1), and two equivalent Ni(1) atoms.
Li2MgNi3O8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Li sites. In the first Li site, Li(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form LiO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Li(2)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 12-13°. Both Li(1)-O(3) bond lengths are 2.09 Å. All Li(1)-O(1) bond lengths are 2.08 Å. In the second Li site, Li(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form LiO6 octahedra that share corners with six equivalent Ni(2)O6 octahedra, edges with two equivalent Li(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-12°. Both Li(2)-O(2) bond lengths are 2.20 Å. All Li(2)-O(1) bond lengths are 2.19 Å. Mg(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Li(1)O6 octahedra, edges with two equivalent Li(2)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 12-13°. Both Mg(1)-O(3) bond lengths are 2.02 Å. All Mg(1)-O(1) bond lengths are 2.02 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share edges with two equivalent Li(1)O6 octahedra, edges with two equivalent Li(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with two equivalent Ni(2)O6 octahedra. Both Ni(1)-O(1) bond lengths are 1.87 Å. Both Ni(1)-O(2) bond lengths are 1.89 Å. Both Ni(1)-O(3) bond lengths are 1.87 Å. In the second Ni site, Ni(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Li(2)O6 octahedra, edges with two equivalent Li(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-12°. Both Ni(2)-O(2) bond lengths are 1.91 Å. All Ni(2)-O(1) bond lengths are 1.91 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Li(1), one Li(2), one Mg(1), one Ni(1), and one Ni(2) atom to form a mixture of edge and corner-sharing OLi2MgNi2 square pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Li(2), one Ni(2), and two equivalent Ni(1) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Li(1), one Mg(1), and two equivalent Ni(1) atoms.