Ba3SrMg2(Si2O7)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one O(1), one O(5), two equivalent O(4), two equivalent O(8), and two equivalent O(9) atoms. Sr(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), two equivalent O(4), two equivalent O(6), and two equivalent O(7) atoms. Mg(1) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form MgO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(3), and two equivalent O(6) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(3)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(1), one O(4), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. In the third Si site, Si(3) is bonded to one O(2), one O(5), and two equivalent O(8) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ba(2), one Sr(1), and two equivalent Si(2) atoms. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Si(1), and one Si(3) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Sr(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Sr(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ba(2), two equivalent Ba(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Mg(1), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Sr(1), one Mg(1), and one Si(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), and one Si(3) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), and one Si(2) atom.
Ba3SrMg2(Si2O7)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The Ba(1)-O(2) bond length is 2.81 Å. The Ba(1)-O(3) bond length is 2.92 Å. The Ba(1)-O(4) bond length is 2.73 Å. The Ba(1)-O(5) bond length is 2.85 Å. The Ba(1)-O(6) bond length is 2.96 Å. The Ba(1)-O(7) bond length is 2.73 Å. The Ba(1)-O(8) bond length is 2.91 Å. The Ba(1)-O(9) bond length is 2.73 Å. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to one O(1), one O(5), two equivalent O(4), two equivalent O(8), and two equivalent O(9) atoms. The Ba(2)-O(1) bond length is 2.76 Å. The Ba(2)-O(5) bond length is 2.67 Å. Both Ba(2)-O(4) bond lengths are 2.82 Å. Both Ba(2)-O(8) bond lengths are 2.75 Å. Both Ba(2)-O(9) bond lengths are 2.97 Å. Sr(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), two equivalent O(4), two equivalent O(6), and two equivalent O(7) atoms. The Sr(1)-O(1) bond length is 2.68 Å. The Sr(1)-O(3) bond length is 2.53 Å. Both Sr(1)-O(4) bond lengths are 2.79 Å. Both Sr(1)-O(6) bond lengths are 2.60 Å. Both Sr(1)-O(7) bond lengths are 2.89 Å. Mg(1) is bonded to one O(6), one O(7), one O(8), and one O(9) atom to form MgO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(3)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The Mg(1)-O(6) bond length is 1.99 Å. The Mg(1)-O(7) bond length is 1.98 Å. The Mg(1)-O(8) bond length is 1.99 Å. The Mg(1)-O(9) bond length is 1.99 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(3), and two equivalent O(6) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(3)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. The Si(1)-O(2) bond length is 1.69 Å. The Si(1)-O(3) bond length is 1.63 Å. Both Si(1)-O(6) bond lengths are 1.65 Å. In the second Si site, Si(2) is bonded to one O(1), one O(4), one O(7), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(2)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. The Si(2)-O(1) bond length is 1.69 Å. The Si(2)-O(4) bond length is 1.63 Å. The Si(2)-O(7) bond length is 1.65 Å. The Si(2)-O(9) bond length is 1.65 Å. In the third Si site, Si(3) is bonded to one O(2), one O(5), and two equivalent O(8) atoms to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. The Si(3)-O(2) bond length is 1.69 Å. The Si(3)-O(5) bond length is 1.62 Å. Both Si(3)-O(8) bond lengths are 1.65 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ba(2), one Sr(1), and two equivalent Si(2) atoms. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Si(1), and one Si(3) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Sr(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Ba(1), one Ba(2), one Sr(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ba(2), two equivalent Ba(1), and one Si(3) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Mg(1), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Sr(1), one Mg(1), and one Si(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), and one Si(3) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), and one Si(2) atom.