Na4P2O7 crystallizes in the orthorhombic P2_12_12_1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom. In the second Na site, Na(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted NaO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(5), and two equivalent O(6) atoms. In the fourth Na site, Na(4) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(5) atom. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 25-58°. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 45-67°. There are seven inequivalent O sites. In the first O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), one Na(3), one Na(4), and one P(2) atom. In the second O site, O(4) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(3), and one P(1) atom. In the third O site, O(5) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), and one P(1) atom. In the fourth O site, O(6) is bonded in a 1-coordinate geometry to one Na(1), one Na(2), two equivalent Na(3), and one P(1) atom. In the fifth O site, O(7) is bonded in a distorted trigonal planar geometry to one Na(1), one P(1), and one P(2) atom. In the sixth O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Na(4), and one P(2) atom. In the seventh O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(4), and one P(2) atom.
Na4P2O7 crystallizes in the orthorhombic P2_12_12_1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom. The Na(1)-O(1) bond length is 2.40 Å. The Na(1)-O(2) bond length is 2.36 Å. The Na(1)-O(4) bond length is 2.29 Å. The Na(1)-O(5) bond length is 2.30 Å. The Na(1)-O(6) bond length is 2.77 Å. The Na(1)-O(7) bond length is 2.39 Å. In the second Na site, Na(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted NaO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. The Na(2)-O(1) bond length is 2.33 Å. The Na(2)-O(2) bond length is 2.66 Å. The Na(2)-O(3) bond length is 2.35 Å. The Na(2)-O(4) bond length is 2.34 Å. The Na(2)-O(5) bond length is 2.47 Å. The Na(2)-O(6) bond length is 2.47 Å. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(5), and two equivalent O(6) atoms. The Na(3)-O(3) bond length is 2.32 Å. The Na(3)-O(4) bond length is 2.39 Å. The Na(3)-O(5) bond length is 2.54 Å. There is one shorter (2.32 Å) and one longer (2.39 Å) Na(3)-O(6) bond length. In the fourth Na site, Na(4) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(5) atom. The Na(4)-O(1) bond length is 2.31 Å. The Na(4)-O(2) bond length is 2.26 Å. The Na(4)-O(3) bond length is 2.29 Å. The Na(4)-O(5) bond length is 2.40 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 25-58°. The P(1)-O(4) bond length is 1.51 Å. The P(1)-O(5) bond length is 1.52 Å. The P(1)-O(6) bond length is 1.52 Å. The P(1)-O(7) bond length is 1.63 Å. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Na(2)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 45-67°. The P(2)-O(1) bond length is 1.52 Å. The P(2)-O(2) bond length is 1.52 Å. The P(2)-O(3) bond length is 1.51 Å. The P(2)-O(7) bond length is 1.65 Å. There are seven inequivalent O sites. In the first O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), one Na(3), one Na(4), and one P(2) atom. In the second O site, O(4) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(3), and one P(1) atom. In the third O site, O(5) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), and one P(1) atom. In the fourth O site, O(6) is bonded in a 1-coordinate geometry to one Na(1), one Na(2), two equivalent Na(3), and one P(1) atom. In the fifth O site, O(7) is bonded in a distorted trigonal planar geometry to one Na(1), one P(1), and one P(2) atom. In the sixth O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Na(4), and one P(2) atom. In the seventh O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(4), and one P(2) atom.