MgMnO2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mn(4)O5 trigonal bipyramid, edges with two equivalent Mg(1)O5 trigonal bipyramids, and  a faceface with one Mn(2)O5 trigonal bipyramid. In the second Mg site, Mg(2) is bonded to one O(1), two equivalent O(5), and two equivalent O(8) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mn(1)O5 trigonal bipyramid, edges with two equivalent Mg(2)O5 trigonal bipyramids, and  a faceface with one Mn(3)O5 trigonal bipyramid. In the third Mg site, Mg(3) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids,  an edgeedge with one Mn(2)O5 trigonal bipyramid, and edges with two equivalent Mn(4)O5 trigonal bipyramids. In the fourth Mg site, Mg(4) is bonded to one O(5), one O(6), and two equivalent O(2) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids,  an edgeedge with one Mn(3)O5 trigonal bipyramid, and edges with two equivalent Mn(1)O5 trigonal bipyramids. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids, edges with two equivalent Mg(4)O4 tetrahedra,  an edgeedge with one Mg(2)O5 trigonal bipyramid, and edges with two equivalent Mn(1)O5 trigonal bipyramids. In the second Mn site, Mn(2) is bonded to one O(4), two equivalent O(3), and two equivalent O(6) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mg(3)O4 tetrahedra, edges with two equivalent Mn(2)O5 trigonal bipyramids, and  a faceface with one Mg(1)O5 trigonal bipyramid. In the third Mn site, Mn(3) is bonded to one O(1), two equivalent O(2), and two equivalent O(8) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mg(4)O4 tetrahedra, edges with two equivalent Mn(3)O5 trigonal bipyramids, and  a faceface with one Mg(2)O5 trigonal bipyramid. In the fourth Mn site, Mn(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids, edges with two equivalent Mg(3)O4 tetrahedra,  an edgeedge with one Mg(1)O5 trigonal bipyramid, and edges with two equivalent Mn(4)O5 trigonal bipyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Mn(3), and two equivalent Mn(4) atoms to form distorted OMgMn3 tetrahedra that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(2)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(3)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(5)Mg3Mn2 trigonal bipyramids, corners with two equivalent O(7)Mg3Mn2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Mn2 trigonal bipyramid. In the second O site, O(2) is bonded to two equivalent Mg(4), one Mn(1), and two equivalent Mn(3) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra, edges with two equivalent O(2)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Mn2 trigonal bipyramids. In the third O site, O(3) is bonded to two equivalent Mg(3), one Mn(4), and two equivalent Mn(2) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra, edges with two equivalent O(3)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(7)Mg3Mn2 trigonal bipyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form distorted OMgMn3 tetrahedra that share corners with two equivalent O(4)MgMn3 tetrahedra, corners with two equivalent O(2)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(3)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(5)Mg3Mn2 trigonal bipyramids, corners with two equivalent O(7)Mg3Mn2 trigonal bipyramids, and  an edgeedge with one O(5)Mg3Mn2 trigonal bipyramid. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and two equivalent Mn(1) atoms to form distorted OMg3Mn2 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra,  an edgeedge with one O(4)MgMn3 tetrahedra, edges with two equivalent O(2)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Mn2 trigonal bipyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(4), two equivalent Mg(1), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded to one Mg(3), two equivalent Mg(1), and two equivalent Mn(4) atoms to form distorted OMg3Mn2 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra,  an edgeedge with one O(1)MgMn3 tetrahedra, edges with two equivalent O(3)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(7)Mg3Mn2 trigonal bipyramids. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(2), and two equivalent Mn(3) atoms.
MgMnO2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mn(4)O5 trigonal bipyramid, edges with two equivalent Mg(1)O5 trigonal bipyramids, and  a faceface with one Mn(2)O5 trigonal bipyramid. The Mg(1)-O(4) bond length is 2.04 Å. There is one shorter (2.15 Å) and one longer (2.18 Å) Mg(1)-O(6) bond length. There is one shorter (2.07 Å) and one longer (2.08 Å) Mg(1)-O(7) bond length. In the second Mg site, Mg(2) is bonded to one O(1), two equivalent O(5), and two equivalent O(8) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mn(1)O5 trigonal bipyramid, edges with two equivalent Mg(2)O5 trigonal bipyramids, and  a faceface with one Mn(3)O5 trigonal bipyramid. The Mg(2)-O(1) bond length is 2.04 Å. There is one shorter (2.07 Å) and one longer (2.08 Å) Mg(2)-O(5) bond length. There is one shorter (2.16 Å) and one longer (2.17 Å) Mg(2)-O(8) bond length. In the third Mg site, Mg(3) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids,  an edgeedge with one Mn(2)O5 trigonal bipyramid, and edges with two equivalent Mn(4)O5 trigonal bipyramids. The Mg(3)-O(7) bond length is 1.99 Å. The Mg(3)-O(8) bond length is 1.94 Å. Both Mg(3)-O(3) bond lengths are 2.03 Å. In the fourth Mg site, Mg(4) is bonded to one O(5), one O(6), and two equivalent O(2) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids,  an edgeedge with one Mn(3)O5 trigonal bipyramid, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The Mg(4)-O(5) bond length is 1.99 Å. The Mg(4)-O(6) bond length is 1.94 Å. Both Mg(4)-O(2) bond lengths are 2.03 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids, edges with two equivalent Mg(4)O4 tetrahedra,  an edgeedge with one Mg(2)O5 trigonal bipyramid, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The Mn(1)-O(2) bond length is 2.24 Å. There is one shorter (2.05 Å) and one longer (2.06 Å) Mn(1)-O(4) bond length. There is one shorter (2.31 Å) and one longer (2.33 Å) Mn(1)-O(5) bond length. In the second Mn site, Mn(2) is bonded to one O(4), two equivalent O(3), and two equivalent O(6) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mg(3)O4 tetrahedra, edges with two equivalent Mn(2)O5 trigonal bipyramids, and  a faceface with one Mg(1)O5 trigonal bipyramid. The Mn(2)-O(4) bond length is 2.07 Å. There is one shorter (2.20 Å) and one longer (2.21 Å) Mn(2)-O(3) bond length. There is one shorter (2.23 Å) and one longer (2.33 Å) Mn(2)-O(6) bond length. In the third Mn site, Mn(3) is bonded to one O(1), two equivalent O(2), and two equivalent O(8) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(4)O4 tetrahedra, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(1)O5 trigonal bipyramids, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mg(4)O4 tetrahedra, edges with two equivalent Mn(3)O5 trigonal bipyramids, and  a faceface with one Mg(2)O5 trigonal bipyramid. The Mn(3)-O(1) bond length is 2.08 Å. There is one shorter (2.19 Å) and one longer (2.23 Å) Mn(3)-O(2) bond length. There is one shorter (2.25 Å) and one longer (2.31 Å) Mn(3)-O(8) bond length. In the fourth Mn site, Mn(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Mn(2)O5 trigonal bipyramids, corners with two equivalent Mn(3)O5 trigonal bipyramids, edges with two equivalent Mg(3)O4 tetrahedra,  an edgeedge with one Mg(1)O5 trigonal bipyramid, and edges with two equivalent Mn(4)O5 trigonal bipyramids. The Mn(4)-O(3) bond length is 2.24 Å. There is one shorter (2.05 Å) and one longer (2.06 Å) Mn(4)-O(1) bond length. There is one shorter (2.28 Å) and one longer (2.36 Å) Mn(4)-O(7) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Mn(3), and two equivalent Mn(4) atoms to form distorted OMgMn3 tetrahedra that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(2)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(3)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(5)Mg3Mn2 trigonal bipyramids, corners with two equivalent O(7)Mg3Mn2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Mn2 trigonal bipyramid. In the second O site, O(2) is bonded to two equivalent Mg(4), one Mn(1), and two equivalent Mn(3) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra, edges with two equivalent O(2)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Mn2 trigonal bipyramids. In the third O site, O(3) is bonded to two equivalent Mg(3), one Mn(4), and two equivalent Mn(2) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra, edges with two equivalent O(3)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(7)Mg3Mn2 trigonal bipyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form distorted OMgMn3 tetrahedra that share corners with two equivalent O(4)MgMn3 tetrahedra, corners with two equivalent O(2)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(3)Mg2Mn3 trigonal bipyramids, corners with two equivalent O(5)Mg3Mn2 trigonal bipyramids, corners with two equivalent O(7)Mg3Mn2 trigonal bipyramids, and  an edgeedge with one O(5)Mg3Mn2 trigonal bipyramid. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and two equivalent Mn(1) atoms to form distorted OMg3Mn2 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra,  an edgeedge with one O(4)MgMn3 tetrahedra, edges with two equivalent O(2)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Mn2 trigonal bipyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(4), two equivalent Mg(1), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded to one Mg(3), two equivalent Mg(1), and two equivalent Mn(4) atoms to form distorted OMg3Mn2 trigonal bipyramids that share corners with two equivalent O(1)MgMn3 tetrahedra, corners with two equivalent O(4)MgMn3 tetrahedra,  an edgeedge with one O(1)MgMn3 tetrahedra, edges with two equivalent O(3)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(7)Mg3Mn2 trigonal bipyramids. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(2), and two equivalent Mn(3) atoms.