Na2Si2O5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(4), and three equivalent O(2) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra,  an edgeedge with one Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 28-72°. In the second Na site, Na(2) is bonded to one O(2), one O(3), one O(5), and three equivalent O(1) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 22°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Na(1)O5 trigonal bipyramid, and edges with two equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 63-68°. In the second Si site, Si(2) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-52°. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(1) atoms. In the second O site, O(1) is bonded in a 5-coordinate geometry to one Na(1), three equivalent Na(2), and one Si(1) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Na(2), three equivalent Na(1), and one Si(2) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom. In the fifth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(2) atoms.
Na2Si2O5 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), one O(4), and three equivalent O(2) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra,  an edgeedge with one Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 28-72°. The Na(1)-O(1) bond length is 2.28 Å. The Na(1)-O(4) bond length is 2.44 Å. There are a spread of Na(1)-O(2) bond distances ranging from 2.32-2.58 Å. In the second Na site, Na(2) is bonded to one O(2), one O(3), one O(5), and three equivalent O(1) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 22°. The Na(2)-O(2) bond length is 2.39 Å. The Na(2)-O(3) bond length is 2.45 Å. The Na(2)-O(5) bond length is 2.39 Å. There are a spread of Na(2)-O(1) bond distances ranging from 2.37-2.55 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Na(1)O5 trigonal bipyramid, and edges with two equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 63-68°. The Si(1)-O(1) bond length is 1.58 Å. The Si(1)-O(3) bond length is 1.65 Å. Both Si(1)-O(5) bond lengths are 1.64 Å. In the second Si site, Si(2) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-52°. The Si(2)-O(2) bond length is 1.59 Å. The Si(2)-O(3) bond length is 1.64 Å. There is one shorter (1.64 Å) and one longer (1.65 Å) Si(2)-O(4) bond length. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(1) atoms. In the second O site, O(1) is bonded in a 5-coordinate geometry to one Na(1), three equivalent Na(2), and one Si(1) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Na(2), three equivalent Na(1), and one Si(2) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom. In the fifth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(2) atoms.