MgCu2(SiO3)4 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with four equivalent Si(2)O4 tetrahedra. Cu(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(5) atom. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-55°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Cu(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom.
MgCu2(SiO3)4 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with four equivalent Si(2)O4 tetrahedra. Both Mg(1)-O(1) bond lengths are 2.02 Å. Both Mg(1)-O(2) bond lengths are 2.04 Å. Both Mg(1)-O(5) bond lengths are 2.30 Å. Cu(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(5) atom. The Cu(1)-O(1) bond length is 1.86 Å. The Cu(1)-O(2) bond length is 1.89 Å. The Cu(1)-O(3) bond length is 1.82 Å. The Cu(1)-O(5) bond length is 1.87 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(6) atom to form SiO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra and corners with two equivalent Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. The Si(1)-O(1) bond length is 1.66 Å. The Si(1)-O(3) bond length is 1.62 Å. The Si(1)-O(4) bond length is 1.64 Å. The Si(1)-O(6) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form SiO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-55°. The Si(2)-O(2) bond length is 1.66 Å. The Si(2)-O(4) bond length is 1.64 Å. The Si(2)-O(5) bond length is 1.65 Å. The Si(2)-O(6) bond length is 1.63 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one Si(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one Si(1) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Mg(1), one Cu(1), and one Si(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom.