Mg3Si4(SbO7)2 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted see-saw-like geometry to one O(1), one O(2), and two equivalent O(7) atoms. In the second Mg site, Mg(2) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with four equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Mg(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. In the second Sb site, Sb(2) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Mg(2), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Sb(1), and one Sb(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(2), one Si(2), and one Sb(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Si(1), one Sb(1), and one Sb(2) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one Si(1) atom.
Mg3Si4(SbO7)2 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted see-saw-like geometry to one O(1), one O(2), and two equivalent O(7) atoms. The Mg(1)-O(1) bond length is 2.13 Å. The Mg(1)-O(2) bond length is 2.00 Å. There is one shorter (2.01 Å) and one longer (2.04 Å) Mg(1)-O(7) bond length. In the second Mg site, Mg(2) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with four equivalent Si(2)O4 tetrahedra. Both Mg(2)-O(1) bond lengths are 2.10 Å. Both Mg(2)-O(3) bond lengths are 2.03 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. The Si(1)-O(4) bond length is 1.66 Å. The Si(1)-O(5) bond length is 1.64 Å. The Si(1)-O(6) bond length is 1.64 Å. The Si(1)-O(7) bond length is 1.63 Å. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Mg(2)O4 tetrahedra and corners with two equivalent Si(1)O4 tetrahedra. The Si(2)-O(1) bond length is 1.69 Å. The Si(2)-O(3) bond length is 1.62 Å. The Si(2)-O(5) bond length is 1.66 Å. The Si(2)-O(6) bond length is 1.67 Å. There are two inequivalent Sb sites. In the first Sb site, Sb(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Both Sb(1)-O(2) bond lengths are 2.07 Å. Both Sb(1)-O(3) bond lengths are 2.60 Å. Both Sb(1)-O(4) bond lengths are 2.35 Å. In the second Sb site, Sb(2) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Sb(2)-O(2) bond lengths are 2.17 Å. Both Sb(2)-O(4) bond lengths are 2.21 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Mg(2), and one Si(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Sb(1), and one Sb(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(2), one Si(2), and one Sb(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Si(1), one Sb(1), and one Sb(2) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one Si(1) atom.