MgCo2(SiO3)4 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(4) and two equivalent O(6) atoms to form distorted MgO4 trigonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Co(2)O4 tetrahedra. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(3) and two equivalent O(5) atoms to form distorted CoO4 tetrahedra that share corners with two equivalent Co(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. In the second Co site, Co(2) is bonded to two equivalent O(5) and two equivalent O(6) atoms to form CoO4 tetrahedra that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Mg(1)O4 trigonal pyramid. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(2)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  a cornercorner with one Mg(1)O4 trigonal pyramid. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  a cornercorner with one Mg(1)O4 trigonal pyramid. There are six inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Co(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Mg(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Co(1), one Co(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(1), one Co(2), and one Si(1) atom.
MgCo2(SiO3)4 crystallizes in the monoclinic C2 space group. Mg(1) is bonded to two equivalent O(4) and two equivalent O(6) atoms to form distorted MgO4 trigonal pyramids that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Co(2)O4 tetrahedra. Both Mg(1)-O(4) bond lengths are 1.87 Å. Both Mg(1)-O(6) bond lengths are 2.02 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(3) and two equivalent O(5) atoms to form distorted CoO4 tetrahedra that share corners with two equivalent Co(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. Both Co(1)-O(3) bond lengths are 1.79 Å. Both Co(1)-O(5) bond lengths are 2.06 Å. In the second Co site, Co(2) is bonded to two equivalent O(5) and two equivalent O(6) atoms to form CoO4 tetrahedra that share corners with two equivalent Co(1)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Mg(1)O4 trigonal pyramid. Both Co(2)-O(5) bond lengths are 1.88 Å. Both Co(2)-O(6) bond lengths are 1.90 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(2)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  a cornercorner with one Mg(1)O4 trigonal pyramid. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(2) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.65 Å. The Si(1)-O(6) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Co(1)O4 tetrahedra,  a cornercorner with one Co(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  a cornercorner with one Mg(1)O4 trigonal pyramid. The Si(2)-O(1) bond length is 1.65 Å. The Si(2)-O(2) bond length is 1.66 Å. The Si(2)-O(4) bond length is 1.57 Å. The Si(2)-O(5) bond length is 1.71 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Co(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Mg(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Co(1), one Co(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mg(1), one Co(2), and one Si(1) atom.