MgCo4O9 crystallizes in the monoclinic Pc space group. Mg(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), one O(7), one O(8), and one O(9) atom to form a mixture of distorted corner and edge-sharing CoO5 trigonal bipyramids. In the second Co site, Co(2) is bonded in a 5-coordinate geometry to one O(1), one O(5), one O(6), one O(7), and one O(9) atom. In the third Co site, Co(3) is bonded to one O(1), one O(3), one O(6), one O(7), and one O(8) atom to form a mixture of distorted corner and edge-sharing CoO5 trigonal bipyramids. In the fourth Co site, Co(4) is bonded to one O(1), one O(2), one O(6), one O(8), and one O(9) atom to form a mixture of distorted corner and edge-sharing CoO5 trigonal bipyramids. There are nine inequivalent O sites. In the first O site, O(1) is bonded to one Co(1), one Co(2), one Co(3), and one Co(4) atom to form a mixture of distorted corner and edge-sharing OCo4 trigonal pyramids. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(4) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(2) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Co(2), one Co(3), and one Co(4) atom. In the seventh O site, O(7) is bonded to one Mg(1), one Co(1), one Co(2), and one Co(3) atom to form a mixture of distorted corner and edge-sharing OMgCo3 tetrahedra. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Mg(1), one Co(1), one Co(3), and one Co(4) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Mg(1), one Co(1), one Co(2), and one Co(4) atom.
MgCo4O9 crystallizes in the monoclinic Pc space group. Mg(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The Mg(1)-O(2) bond length is 2.21 Å. The Mg(1)-O(3) bond length is 2.17 Å. The Mg(1)-O(4) bond length is 2.21 Å. The Mg(1)-O(5) bond length is 2.18 Å. The Mg(1)-O(6) bond length is 2.38 Å. The Mg(1)-O(7) bond length is 2.29 Å. The Mg(1)-O(8) bond length is 2.40 Å. The Mg(1)-O(9) bond length is 2.36 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), one O(7), one O(8), and one O(9) atom to form a mixture of distorted corner and edge-sharing CoO5 trigonal bipyramids. The Co(1)-O(1) bond length is 2.00 Å. The Co(1)-O(4) bond length is 1.65 Å. The Co(1)-O(7) bond length is 1.94 Å. The Co(1)-O(8) bond length is 1.97 Å. The Co(1)-O(9) bond length is 1.90 Å. In the second Co site, Co(2) is bonded in a 5-coordinate geometry to one O(1), one O(5), one O(6), one O(7), and one O(9) atom. The Co(2)-O(1) bond length is 1.99 Å. The Co(2)-O(5) bond length is 1.66 Å. The Co(2)-O(6) bond length is 1.94 Å. The Co(2)-O(7) bond length is 1.92 Å. The Co(2)-O(9) bond length is 1.95 Å. In the third Co site, Co(3) is bonded to one O(1), one O(3), one O(6), one O(7), and one O(8) atom to form a mixture of distorted corner and edge-sharing CoO5 trigonal bipyramids. The Co(3)-O(1) bond length is 2.00 Å. The Co(3)-O(3) bond length is 1.66 Å. The Co(3)-O(6) bond length is 1.89 Å. The Co(3)-O(7) bond length is 1.98 Å. The Co(3)-O(8) bond length is 1.92 Å. In the fourth Co site, Co(4) is bonded to one O(1), one O(2), one O(6), one O(8), and one O(9) atom to form a mixture of distorted corner and edge-sharing CoO5 trigonal bipyramids. The Co(4)-O(1) bond length is 1.98 Å. The Co(4)-O(2) bond length is 1.66 Å. The Co(4)-O(6) bond length is 1.95 Å. The Co(4)-O(8) bond length is 1.92 Å. The Co(4)-O(9) bond length is 1.95 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded to one Co(1), one Co(2), one Co(3), and one Co(4) atom to form a mixture of distorted corner and edge-sharing OCo4 trigonal pyramids. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(4) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(3) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(1) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one Co(2) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Co(2), one Co(3), and one Co(4) atom. In the seventh O site, O(7) is bonded to one Mg(1), one Co(1), one Co(2), and one Co(3) atom to form a mixture of distorted corner and edge-sharing OMgCo3 tetrahedra. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Mg(1), one Co(1), one Co(3), and one Co(4) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Mg(1), one Co(1), one Co(2), and one Co(4) atom.