Ba3MgNb2CoO9 is Orthorhombic Perovskite-derived structured and crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 11-coordinate geometry to one Co(1), one O(4), two equivalent O(1), three equivalent O(2), and four equivalent O(3) atoms. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to two equivalent O(4), four equivalent O(1), and four equivalent O(3) atoms. Mg(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form distorted MgO6 octahedra that share faces with two equivalent Nb(1)O6 octahedra. 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 three equivalent Nb(1)O6 octahedra and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedra are not tilted. Co(1) is bonded in a distorted square co-planar geometry to two equivalent Ba(1) and four equivalent O(3) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to three equivalent Ba(1), one Mg(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ba(2), two equivalent Ba(1), one Mg(1), one Nb(1), and one Co(1) atom. In the fourth O site, O(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Nb(1) atoms to form distorted corner-sharing OBa4Nb2 octahedra. The corner-sharing octahedra are not tilted.
Ba3MgNb2CoO9 is Orthorhombic Perovskite-derived structured and crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 11-coordinate geometry to one Co(1), one O(4), two equivalent O(1), three equivalent O(2), and four equivalent O(3) atoms. The Ba(1)-Co(1) bond length is 2.94 Å. The Ba(1)-O(4) bond length is 2.91 Å. Both Ba(1)-O(1) bond lengths are 2.91 Å. There is one shorter (2.78 Å) and two longer (2.95 Å) Ba(1)-O(2) bond lengths. There are two shorter (2.91 Å) and two longer (3.24 Å) Ba(1)-O(3) bond lengths. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to two equivalent O(4), four equivalent O(1), and four equivalent O(3) atoms. Both Ba(2)-O(4) bond lengths are 2.87 Å. All Ba(2)-O(1) bond lengths are 3.08 Å. All Ba(2)-O(3) bond lengths are 2.87 Å. Mg(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form distorted MgO6 octahedra that share faces with two equivalent Nb(1)O6 octahedra. Both Mg(1)-O(2) bond lengths are 2.28 Å. All Mg(1)-O(3) bond lengths are 2.07 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 three equivalent Nb(1)O6 octahedra and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedra are not tilted. The Nb(1)-O(2) bond length is 1.99 Å. The Nb(1)-O(4) bond length is 2.13 Å. Both Nb(1)-O(1) bond lengths are 2.09 Å. Both Nb(1)-O(3) bond lengths are 2.05 Å. Co(1) is bonded in a distorted square co-planar geometry to two equivalent Ba(1) and four equivalent O(3) atoms. All Co(1)-O(3) bond lengths are 2.11 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to three equivalent Ba(1), one Mg(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ba(2), two equivalent Ba(1), one Mg(1), one Nb(1), and one Co(1) atom. In the fourth O site, O(4) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Nb(1) atoms to form distorted corner-sharing OBa4Nb2 octahedra. The corner-sharing octahedra are not tilted.