MgSi4(MoO6)2 crystallizes in the monoclinic C2 space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. There are two inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form MoO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Mo(2)O6 octahedra. In the second Mo site, Mo(2) is bonded to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form MoO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mo(1)O6 octahedra. 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 Mo(2)O6 octahedra, corners with two equivalent Mo(1)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-57°. 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 Mo(1)O6 octahedra, corners with two equivalent Mo(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-60°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Mo(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Mo(2) and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), one Mo(1), one Mo(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mo(1), one Mo(2), and one Si(1) atom.
MgSi4(MoO6)2 crystallizes in the monoclinic C2 space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. Both Mg(1)-O(2) bond lengths are 2.41 Å. Both Mg(1)-O(3) bond lengths are 2.05 Å. Both Mg(1)-O(5) bond lengths are 2.21 Å. There are two inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form MoO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, and edges with two equivalent Mo(2)O6 octahedra. Both Mo(1)-O(3) bond lengths are 2.13 Å. Both Mo(1)-O(5) bond lengths are 2.17 Å. Both Mo(1)-O(6) bond lengths are 2.17 Å. In the second Mo site, Mo(2) is bonded to two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form MoO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Si(2)O4 tetrahedra, and edges with two equivalent Mo(1)O6 octahedra. Both Mo(2)-O(4) bond lengths are 2.06 Å. Both Mo(2)-O(5) bond lengths are 2.27 Å. Both Mo(2)-O(6) bond lengths are 2.17 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 Mo(2)O6 octahedra, corners with two equivalent Mo(1)O6 octahedra, and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-57°. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(2) bond length is 1.67 Å. The Si(1)-O(3) bond length is 1.63 Å. The Si(1)-O(6) bond length is 1.64 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 Mo(1)O6 octahedra, corners with two equivalent Mo(2)O6 octahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 33-60°. The Si(2)-O(1) bond length is 1.64 Å. The Si(2)-O(2) bond length is 1.68 Å. The Si(2)-O(4) bond length is 1.58 Å. The Si(2)-O(5) bond length is 1.68 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Mo(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Mo(2) and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), one Mo(1), one Mo(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Mo(1), one Mo(2), and one Si(1) atom.