SrBaMgSi2O7 crystallizes in the monoclinic P2_1 space group. Ba(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(6), two equivalent O(3), and two equivalent O(7) atoms. Sr(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(7), two equivalent O(2), and two equivalent O(6) atoms. Mg(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form MgO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(5), and one O(6) 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 second Si site, Si(2) is bonded to one O(1), one O(3), one O(4), and one O(7) atom 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 seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Mg(1), and one Si(2) atom. In the fourth O site, O(4) 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 fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Mg(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Sr(1), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to two equivalent Ba(1), one Sr(1), and one Si(2) atom.
SrBaMgSi2O7 crystallizes in the monoclinic P2_1 space group. Ba(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(6), two equivalent O(3), and two equivalent O(7) atoms. The Ba(1)-O(1) bond length is 2.77 Å. The Ba(1)-O(4) bond length is 2.75 Å. The Ba(1)-O(5) bond length is 2.97 Å. The Ba(1)-O(6) bond length is 2.89 Å. There is one shorter (2.74 Å) and one longer (2.92 Å) Ba(1)-O(3) bond length. There is one shorter (2.71 Å) and one longer (2.82 Å) Ba(1)-O(7) bond length. Sr(1) is bonded in a 8-coordinate geometry to one O(1), one O(4), one O(5), one O(7), two equivalent O(2), and two equivalent O(6) atoms. The Sr(1)-O(1) bond length is 2.65 Å. The Sr(1)-O(4) bond length is 2.79 Å. The Sr(1)-O(5) bond length is 2.58 Å. The Sr(1)-O(7) bond length is 2.74 Å. There is one shorter (2.58 Å) and one longer (2.88 Å) Sr(1)-O(2) bond length. There is one shorter (2.56 Å) and one longer (2.86 Å) Sr(1)-O(6) bond length. Mg(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form MgO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. The Mg(1)-O(2) bond length is 1.98 Å. The Mg(1)-O(3) bond length is 1.99 Å. The Mg(1)-O(4) bond length is 1.98 Å. The Mg(1)-O(5) bond length is 1.98 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(5), and one O(6) 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(1)-O(1) bond length is 1.69 Å. The Si(1)-O(2) bond length is 1.65 Å. The Si(1)-O(5) bond length is 1.65 Å. The Si(1)-O(6) bond length is 1.62 Å. In the second Si site, Si(2) is bonded to one O(1), one O(3), one O(4), and one O(7) atom 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(2)-O(1) bond length is 1.69 Å. The Si(2)-O(3) bond length is 1.65 Å. The Si(2)-O(4) bond length is 1.65 Å. The Si(2)-O(7) bond length is 1.62 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Mg(1), and one Si(2) atom. In the fourth O site, O(4) 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 fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ba(1), one Sr(1), one Mg(1), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ba(1), two equivalent Sr(1), and one Si(1) atom. In the seventh O site, O(7) is bonded in a distorted single-bond geometry to two equivalent Ba(1), one Sr(1), and one Si(2) atom.