MgCo4(HgO4)2 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one Co(3), two equivalent Co(1), one O(1), one O(4), and two equivalent O(5) atoms to form MgCo3O4 tetrahedra that share corners with four equivalent Hg(2)O4 tetrahedra. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded in a 7-coordinate geometry to one Mg(1), one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom. In the second Co site, Co(2) is bonded in a 3-coordinate geometry to one O(1), one O(6), two equivalent O(3), and two equivalent O(5) atoms. In the third Co site, Co(3) is bonded in a 7-coordinate geometry to one Mg(1), one O(2), one O(4), two equivalent O(3), and two equivalent O(5) atoms. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a tetrahedral geometry to one O(2), one O(6), and two equivalent O(3) atoms. In the second Hg site, Hg(2) is bonded to one O(1), one O(4), and two equivalent O(5) atoms to form HgO4 tetrahedra that share corners with four equivalent Mg(1)Co3O4 tetrahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Co(2), two equivalent Co(1), and one Hg(2) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Co(3), two equivalent Co(1), and one Hg(1) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Co(1), one Co(2), one Co(3), and one Hg(1) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Mg(1), one Co(3), two equivalent Co(1), and one Hg(2) atom. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(2), one Co(3), and one Hg(2) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Co(2), two equivalent Co(1), and one Hg(1) atom.
MgCo4(HgO4)2 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one Co(3), two equivalent Co(1), one O(1), one O(4), and two equivalent O(5) atoms to form MgCo3O4 tetrahedra that share corners with four equivalent Hg(2)O4 tetrahedra. The Mg(1)-Co(3) bond length is 2.33 Å. Both Mg(1)-Co(1) bond lengths are 2.36 Å. The Mg(1)-O(1) bond length is 1.82 Å. The Mg(1)-O(4) bond length is 1.86 Å. Both Mg(1)-O(5) bond lengths are 1.83 Å. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded in a 7-coordinate geometry to one Mg(1), one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom. The Co(1)-O(1) bond length is 2.43 Å. The Co(1)-O(2) bond length is 2.01 Å. The Co(1)-O(3) bond length is 2.05 Å. The Co(1)-O(4) bond length is 2.42 Å. The Co(1)-O(5) bond length is 2.55 Å. The Co(1)-O(6) bond length is 2.05 Å. In the second Co site, Co(2) is bonded in a 3-coordinate geometry to one O(1), one O(6), two equivalent O(3), and two equivalent O(5) atoms. The Co(2)-O(1) bond length is 2.44 Å. The Co(2)-O(6) bond length is 1.88 Å. Both Co(2)-O(3) bond lengths are 1.99 Å. Both Co(2)-O(5) bond lengths are 2.50 Å. In the third Co site, Co(3) is bonded in a 7-coordinate geometry to one Mg(1), one O(2), one O(4), two equivalent O(3), and two equivalent O(5) atoms. The Co(3)-O(2) bond length is 2.00 Å. The Co(3)-O(4) bond length is 2.23 Å. Both Co(3)-O(3) bond lengths are 1.95 Å. Both Co(3)-O(5) bond lengths are 2.45 Å. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a tetrahedral geometry to one O(2), one O(6), and two equivalent O(3) atoms. The Hg(1)-O(2) bond length is 2.25 Å. The Hg(1)-O(6) bond length is 2.34 Å. Both Hg(1)-O(3) bond lengths are 2.37 Å. In the second Hg site, Hg(2) is bonded to one O(1), one O(4), and two equivalent O(5) atoms to form HgO4 tetrahedra that share corners with four equivalent Mg(1)Co3O4 tetrahedra. The Hg(2)-O(1) bond length is 2.24 Å. The Hg(2)-O(4) bond length is 2.28 Å. Both Hg(2)-O(5) bond lengths are 2.20 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Co(2), two equivalent Co(1), and one Hg(2) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Co(3), two equivalent Co(1), and one Hg(1) atom. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Co(1), one Co(2), one Co(3), and one Hg(1) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Mg(1), one Co(3), two equivalent Co(1), and one Hg(2) atom. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(1), one Co(1), one Co(2), one Co(3), and one Hg(2) atom. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Co(2), two equivalent Co(1), and one Hg(1) atom.