Na2Si2O5 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO5 square pyramids that share corners with four equivalent Na(1)O5 square pyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(5), 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(4), one O(5), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Na(1)O5 square pyramid. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(2) atoms. In the third O site, O(3) is bonded to two equivalent Na(1), two equivalent Na(2), and one Si(2) atom to form distorted corner-sharing ONa4Si trigonal bipyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom.
Na2Si2O5 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO5 square pyramids that share corners with four equivalent Na(1)O5 square pyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. The Na(1)-O(1) bond length is 2.42 Å. There is one shorter (2.36 Å) and one longer (2.37 Å) Na(1)-O(3) bond length. There is one shorter (2.39 Å) and one longer (2.54 Å) Na(1)-O(4) bond length. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(5), two equivalent O(3), and two equivalent O(4) atoms. The Na(2)-O(2) bond length is 2.44 Å. The Na(2)-O(5) bond length is 2.84 Å. There is one shorter (2.37 Å) and one longer (2.55 Å) Na(2)-O(3) bond length. There is one shorter (2.28 Å) and one longer (2.29 Å) Na(2)-O(4) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Na(1)O5 square pyramid. The Si(1)-O(4) bond length is 1.58 Å. The Si(1)-O(5) bond length is 1.64 Å. There is one shorter (1.64 Å) and one longer (1.65 Å) Si(1)-O(1) bond length. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. The Si(2)-O(3) bond length is 1.59 Å. The Si(2)-O(5) bond length is 1.64 Å. There is one shorter (1.64 Å) and one longer (1.65 Å) Si(2)-O(2) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(2) atoms. In the third O site, O(3) is bonded to two equivalent Na(1), two equivalent Na(2), and one Si(2) atom to form distorted corner-sharing ONa4Si trigonal bipyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom.