Mg3Co2O7 crystallizes in the monoclinic Cc space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 8-coordinate geometry to one O(4), one O(5), two equivalent O(1), two equivalent O(6), and two equivalent O(7) atoms. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one O(3), one O(6), two equivalent O(2), and two equivalent O(4) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one O(2), one O(7), two equivalent O(3), and two equivalent O(5) atoms. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(2), two equivalent O(4), and two equivalent O(6) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 39-44°. In the second Co site, Co(2) is bonded to one O(1), one O(3), two equivalent O(5), and two equivalent O(7) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 39-44°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), one Co(1), and one Co(2) atom to form distorted OMg2Co2 trigonal pyramids that share  a cornercorner with one O(2)Mg3Co tetrahedra,  a cornercorner with one O(3)Mg3Co tetrahedra, corners with four equivalent O(6)Mg3Co2 trigonal bipyramids, corners with two equivalent O(1)Mg2Co2 trigonal pyramids, and  an edgeedge with one O(6)Mg3Co2 trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(3), two equivalent Mg(2), and one Co(1) atom to form distorted OMg3Co tetrahedra that share corners with two equivalent O(2)Mg3Co tetrahedra, corners with four equivalent O(3)Mg3Co tetrahedra,  a cornercorner with one O(1)Mg2Co2 trigonal pyramid, and edges with two equivalent O(6)Mg3Co2 trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(2), two equivalent Mg(3), and one Co(2) atom to form distorted OMg3Co tetrahedra that share corners with two equivalent O(3)Mg3Co tetrahedra, corners with four equivalent O(2)Mg3Co tetrahedra,  a cornercorner with one O(6)Mg3Co2 trigonal bipyramid, and  a cornercorner with one O(1)Mg2Co2 trigonal pyramid. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), and two equivalent Co(1) atoms. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Mg(3), and two equivalent Co(2) atoms. In the sixth O site, O(6) is bonded to one Mg(2), two equivalent Mg(1), and two equivalent Co(1) atoms to form distorted OMg3Co2 trigonal bipyramids that share  a cornercorner with one O(3)Mg3Co tetrahedra, corners with four equivalent O(1)Mg2Co2 trigonal pyramids, edges with two equivalent O(2)Mg3Co tetrahedra, edges with two equivalent O(6)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(1)Mg2Co2 trigonal pyramid. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(1), and two equivalent Co(2) atoms.
Mg3Co2O7 crystallizes in the monoclinic Cc space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 8-coordinate geometry to one O(4), one O(5), two equivalent O(1), two equivalent O(6), and two equivalent O(7) atoms. The Mg(1)-O(4) bond length is 2.62 Å. The Mg(1)-O(5) bond length is 2.67 Å. There is one shorter (2.05 Å) and one longer (2.11 Å) Mg(1)-O(1) bond length. There is one shorter (2.10 Å) and one longer (2.26 Å) Mg(1)-O(6) bond length. There is one shorter (2.08 Å) and one longer (2.46 Å) Mg(1)-O(7) bond length. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one O(3), one O(6), two equivalent O(2), and two equivalent O(4) atoms. The Mg(2)-O(3) bond length is 2.02 Å. The Mg(2)-O(6) bond length is 2.32 Å. There is one shorter (2.01 Å) and one longer (2.09 Å) Mg(2)-O(2) bond length. There is one shorter (2.07 Å) and one longer (2.17 Å) Mg(2)-O(4) bond length. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one O(2), one O(7), two equivalent O(3), and two equivalent O(5) atoms. The Mg(3)-O(2) bond length is 2.04 Å. The Mg(3)-O(7) bond length is 2.26 Å. There is one shorter (2.00 Å) and one longer (2.05 Å) Mg(3)-O(3) bond length. There is one shorter (2.08 Å) and one longer (2.26 Å) Mg(3)-O(5) bond length. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(2), two equivalent O(4), and two equivalent O(6) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 39-44°. The Co(1)-O(1) bond length is 1.89 Å. The Co(1)-O(2) bond length is 1.86 Å. There is one shorter (1.94 Å) and one longer (1.95 Å) Co(1)-O(4) bond length. There is one shorter (1.93 Å) and one longer (1.96 Å) Co(1)-O(6) bond length. In the second Co site, Co(2) is bonded to one O(1), one O(3), two equivalent O(5), and two equivalent O(7) atoms to form corner-sharing CoO6 octahedra. The corner-sharing octahedral tilt angles range from 39-44°. The Co(2)-O(1) bond length is 1.97 Å. The Co(2)-O(3) bond length is 1.92 Å. There is one shorter (1.81 Å) and one longer (2.04 Å) Co(2)-O(5) bond length. There is one shorter (1.78 Å) and one longer (2.15 Å) Co(2)-O(7) bond length. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), one Co(1), and one Co(2) atom to form distorted OMg2Co2 trigonal pyramids that share  a cornercorner with one O(2)Mg3Co tetrahedra,  a cornercorner with one O(3)Mg3Co tetrahedra, corners with four equivalent O(6)Mg3Co2 trigonal bipyramids, corners with two equivalent O(1)Mg2Co2 trigonal pyramids, and  an edgeedge with one O(6)Mg3Co2 trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(3), two equivalent Mg(2), and one Co(1) atom to form distorted OMg3Co tetrahedra that share corners with two equivalent O(2)Mg3Co tetrahedra, corners with four equivalent O(3)Mg3Co tetrahedra,  a cornercorner with one O(1)Mg2Co2 trigonal pyramid, and edges with two equivalent O(6)Mg3Co2 trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(2), two equivalent Mg(3), and one Co(2) atom to form distorted OMg3Co tetrahedra that share corners with two equivalent O(3)Mg3Co tetrahedra, corners with four equivalent O(2)Mg3Co tetrahedra,  a cornercorner with one O(6)Mg3Co2 trigonal bipyramid, and  a cornercorner with one O(1)Mg2Co2 trigonal pyramid. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), and two equivalent Co(1) atoms. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Mg(3), and two equivalent Co(2) atoms. In the sixth O site, O(6) is bonded to one Mg(2), two equivalent Mg(1), and two equivalent Co(1) atoms to form distorted OMg3Co2 trigonal bipyramids that share  a cornercorner with one O(3)Mg3Co tetrahedra, corners with four equivalent O(1)Mg2Co2 trigonal pyramids, edges with two equivalent O(2)Mg3Co tetrahedra, edges with two equivalent O(6)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(1)Mg2Co2 trigonal pyramid. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(1), and two equivalent Co(2) atoms.