Na4Sr(SiO3)3 crystallizes in the monoclinic C2 space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra and corners with four equivalent Si(1)O4 tetrahedra. In the second Na site, Na(2) is bonded in a distorted bent 120 degrees geometry to two equivalent O(2) and two equivalent O(4) atoms. In the third Na site, Na(3) is bonded in a distorted bent 120 degrees geometry to one O(4) and two equivalent O(3) atoms. Sr(1) is bonded in a 9-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. 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(5) atom to form SiO4 tetrahedra that share corners with two equivalent Na(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 40°. In the second Si site, Si(2) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to 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 one Na(1), one Na(2), one Sr(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(3), one Sr(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(3), one Sr(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Sr(1) and two equivalent Si(1) atoms.
Na4Sr(SiO3)3 crystallizes in the monoclinic C2 space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra and corners with four equivalent Si(1)O4 tetrahedra. Both Na(1)-O(2) bond lengths are 2.52 Å. Both Na(1)-O(3) bond lengths are 2.50 Å. Both Na(1)-O(4) bond lengths are 2.51 Å. In the second Na site, Na(2) is bonded in a distorted bent 120 degrees geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Na(2)-O(2) bond lengths are 2.26 Å. Both Na(2)-O(4) bond lengths are 2.93 Å. In the third Na site, Na(3) is bonded in a distorted bent 120 degrees geometry to one O(4) and two equivalent O(3) atoms. The Na(3)-O(4) bond length is 2.25 Å. There is one shorter (2.24 Å) and one longer (2.96 Å) Na(3)-O(3) bond length. Sr(1) is bonded in a 9-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The Sr(1)-O(5) bond length is 2.92 Å. Both Sr(1)-O(1) bond lengths are 2.84 Å. Both Sr(1)-O(2) bond lengths are 2.63 Å. Both Sr(1)-O(3) bond lengths are 2.64 Å. Both Sr(1)-O(4) bond lengths are 2.67 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(5) atom to form SiO4 tetrahedra that share corners with two equivalent Na(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 40°. The Si(1)-O(1) bond length is 1.67 Å. The Si(1)-O(2) bond length is 1.61 Å. The Si(1)-O(3) bond length is 1.61 Å. The Si(1)-O(5) bond length is 1.67 Å. In the second Si site, Si(2) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. Both Si(2)-O(1) bond lengths are 1.67 Å. Both Si(2)-O(4) bond lengths are 1.61 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to 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 one Na(1), one Na(2), one Sr(1), and one Si(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(1), two equivalent Na(3), one Sr(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(3), one Sr(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Sr(1) and two equivalent Si(1) atoms.