MgNbMnO4 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mg(1)O5 trigonal bipyramids, edges with two equivalent Mn(1)O6 octahedra, and edges with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-72°. Nb(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, edges with four equivalent Mn(1)O6 octahedra, and edges with four equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-11°. Mn(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, edges with four equivalent Nb(1)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-35°. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), two equivalent Nb(1), and one Mn(1) atom to form a mixture of distorted edge and corner-sharing OMg2MnNb2 square pyramids. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Nb(1) and two equivalent Mn(1) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1), two equivalent Nb(1), and one Mn(1) atom to form a mixture of edge and corner-sharing OMg2MnNb2 trigonal bipyramids. In the fourth O site, O(4) is bonded in a square co-planar geometry to one Mg(1), one Nb(1), and two equivalent Mn(1) atoms.
MgNbMnO4 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mg(1)O5 trigonal bipyramids, edges with two equivalent Mn(1)O6 octahedra, and edges with four equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-72°. The Mg(1)-O(4) bond length is 2.02 Å. Both Mg(1)-O(1) bond lengths are 2.24 Å. Both Mg(1)-O(3) bond lengths are 2.18 Å. Nb(1) is bonded to one O(2), one O(4), two equivalent O(1), and two equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, edges with four equivalent Mn(1)O6 octahedra, and edges with four equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-11°. The Nb(1)-O(2) bond length is 1.95 Å. The Nb(1)-O(4) bond length is 2.07 Å. Both Nb(1)-O(1) bond lengths are 2.08 Å. Both Nb(1)-O(3) bond lengths are 2.19 Å. Mn(1) is bonded to one O(1), one O(3), two equivalent O(2), and two equivalent O(4) atoms to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, edges with four equivalent Nb(1)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 5-35°. The Mn(1)-O(1) bond length is 2.39 Å. The Mn(1)-O(3) bond length is 2.16 Å. Both Mn(1)-O(2) bond lengths are 2.16 Å. Both Mn(1)-O(4) bond lengths are 2.19 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), two equivalent Nb(1), and one Mn(1) atom to form a mixture of distorted edge and corner-sharing OMg2MnNb2 square pyramids. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Nb(1) and two equivalent Mn(1) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1), two equivalent Nb(1), and one Mn(1) atom to form a mixture of edge and corner-sharing OMg2MnNb2 trigonal bipyramids. In the fourth O site, O(4) is bonded in a square co-planar geometry to one Mg(1), one Nb(1), and two equivalent Mn(1) atoms.