MgMn2(NiO3)2 crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Mn(1)O6 octahedra, edges with six equivalent Ni(1)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 42°. Mn(1) is bonded to six equivalent O(1) atoms to form MnO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with nine equivalent Ni(1)O6 octahedra, edges with three equivalent Mn(1)O6 octahedra,  a faceface with one Mg(1)O6 octahedra, and  a faceface with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-55°. Ni(1) is bonded to six equivalent O(1) atoms to form distorted NiO6 octahedra that share corners with nine equivalent Mn(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, edges with three equivalent Ni(1)O6 octahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-55°. O(1) is bonded to one Mg(1), two equivalent Mn(1), and two equivalent Ni(1) atoms to form a mixture of distorted corner and edge-sharing OMgMn2Ni2 trigonal bipyramids.
MgMn2(NiO3)2 crystallizes in the trigonal R-3 space group. Mg(1) is bonded to six equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Mn(1)O6 octahedra, edges with six equivalent Ni(1)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 42°. All Mg(1)-O(1) bond lengths are 2.06 Å. Mn(1) is bonded to six equivalent O(1) atoms to form MnO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with nine equivalent Ni(1)O6 octahedra, edges with three equivalent Mn(1)O6 octahedra,  a faceface with one Mg(1)O6 octahedra, and  a faceface with one Ni(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-55°. There are three shorter (2.03 Å) and three longer (2.15 Å) Mn(1)-O(1) bond lengths. Ni(1) is bonded to six equivalent O(1) atoms to form distorted NiO6 octahedra that share corners with nine equivalent Mn(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, edges with three equivalent Ni(1)O6 octahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-55°. There are three shorter (2.04 Å) and three longer (2.26 Å) Ni(1)-O(1) bond lengths. O(1) is bonded to one Mg(1), two equivalent Mn(1), and two equivalent Ni(1) atoms to form a mixture of distorted corner and edge-sharing OMgMn2Ni2 trigonal bipyramids.