Na2HPO4 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NaO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and edges with two equivalent Na(2)O6 octahedra. In the second Na site, Na(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NaO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and edges with two equivalent Na(1)O6 octahedra. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Na(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-53°. H(1) is bonded in a linear geometry to one O(3) and one O(4) atom. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(3), and one P(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Na(3), and one P(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Na(2), one Na(3), one P(1), and one H(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Na(1), one Na(3), one P(1), and one H(1) atom.
Na2HPO4 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NaO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and edges with two equivalent Na(2)O6 octahedra. Both Na(1)-O(1) bond lengths are 2.48 Å. Both Na(1)-O(2) bond lengths are 2.36 Å. Both Na(1)-O(4) bond lengths are 2.53 Å. In the second Na site, Na(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NaO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra and edges with two equivalent Na(1)O6 octahedra. Both Na(2)-O(1) bond lengths are 2.52 Å. Both Na(2)-O(2) bond lengths are 2.40 Å. Both Na(2)-O(3) bond lengths are 2.42 Å. In the third Na site, Na(3) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Na(3)-O(1) bond length is 2.49 Å. The Na(3)-O(2) bond length is 2.30 Å. The Na(3)-O(3) bond length is 2.34 Å. The Na(3)-O(4) bond length is 2.40 Å. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Na(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 38-53°. The P(1)-O(1) bond length is 1.52 Å. The P(1)-O(2) bond length is 1.53 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(4) bond length is 1.63 Å. H(1) is bonded in a linear geometry to one O(3) and one O(4) atom. The H(1)-O(3) bond length is 1.50 Å. The H(1)-O(4) bond length is 1.04 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Na(3), and one P(1) atom. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Na(3), and one P(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Na(2), one Na(3), one P(1), and one H(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Na(1), one Na(3), one P(1), and one H(1) atom.