Mg2Co3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Co(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra, and edges with three equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. In the second Mg site, Mg(2) is bonded to one O(4) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and corners with nine equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-64°. Co(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form CoO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with four equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mg(1) and two equivalent Co(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and two equivalent Co(1) atoms to form distorted OMg2Co2 tetrahedra that share corners with two equivalent O(2)Mg2Co2 tetrahedra,  a cornercorner with one O(4)MgCo3 trigonal pyramid, edges with two equivalent O(2)Mg2Co2 tetrahedra, and  an edgeedge with one O(4)MgCo3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Co(1) atoms. In the fourth O site, O(4) is bonded to one Mg(2) and three equivalent Co(1) atoms to form a mixture of distorted corner and edge-sharing OMgCo3 trigonal pyramids.
Mg2Co3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Co(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra, and edges with three equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. All Mg(1)-O(1) bond lengths are 2.08 Å. All Mg(1)-O(2) bond lengths are 2.07 Å. In the second Mg site, Mg(2) is bonded to one O(4) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and corners with nine equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-64°. The Mg(2)-O(4) bond length is 1.96 Å. All Mg(2)-O(2) bond lengths are 1.91 Å. Co(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form CoO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with four equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. The Co(1)-O(3) bond length is 1.89 Å. The Co(1)-O(4) bond length is 1.93 Å. Both Co(1)-O(1) bond lengths are 1.82 Å. Both Co(1)-O(2) bond lengths are 1.89 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mg(1) and two equivalent Co(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and two equivalent Co(1) atoms to form distorted OMg2Co2 tetrahedra that share corners with two equivalent O(2)Mg2Co2 tetrahedra,  a cornercorner with one O(4)MgCo3 trigonal pyramid, edges with two equivalent O(2)Mg2Co2 tetrahedra, and  an edgeedge with one O(4)MgCo3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Co(1) atoms. In the fourth O site, O(4) is bonded to one Mg(2) and three equivalent Co(1) atoms to form a mixture of distorted corner and edge-sharing OMgCo3 trigonal pyramids.