MgMn3NiO8 is beta indium sulfide-derived structured and crystallizes in the trigonal R-3m space group. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Ni(1)O6 octahedra and edges with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. Mn(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MnO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. Ni(1) is bonded to six equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra and edges with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a see-saw-like geometry to one Mg(1), two equivalent Mn(1), and one Ni(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to three equivalent Mn(1) atoms.
MgMn3NiO8 is beta indium sulfide-derived structured and crystallizes in the trigonal R-3m space group. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Ni(1)O6 octahedra and edges with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. All Mg(1)-O(1) bond lengths are 2.09 Å. Mn(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MnO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. Both Mn(1)-O(2) bond lengths are 1.97 Å. All Mn(1)-O(1) bond lengths are 1.94 Å. Ni(1) is bonded to six equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra and edges with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 13°. All Ni(1)-O(1) bond lengths are 2.12 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a see-saw-like geometry to one Mg(1), two equivalent Mn(1), and one Ni(1) atom. In the second O site, O(2) is bonded in a distorted T-shaped geometry to three equivalent Mn(1) atoms.