Na6P2H2O9 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(3), one O(4), two equivalent O(2), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 7-coordinate geometry to one H(1), one O(1), one O(3), two equivalent O(2), and two equivalent O(5) atoms. In the third Na site, Na(3) is bonded to one O(1), one O(5), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(3)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra,  an edgeedge with one P(1)O4 tetrahedra, and  a faceface with one Na(3)O6 octahedra. The corner-sharing octahedral tilt angles are 78°. P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Na(3)O6 octahedra and  an edgeedge with one Na(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-69°. H(1) is bonded in a single-bond geometry to one Na(2) and one O(1) atom. There are five inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to two equivalent Na(2), two equivalent Na(3), and two equivalent H(1) atoms. In the second O site, O(2) is bonded to two equivalent Na(1), two equivalent Na(2), and one P(1) atom to form distorted edge-sharing ONa4P square pyramids. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), two equivalent Na(3), and one P(1) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to one Na(1), two equivalent Na(3), and one P(1) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one Na(3), two equivalent Na(1), two equivalent Na(2), and one P(1) atom.
Na6P2H2O9 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(3), one O(4), two equivalent O(2), and two equivalent O(5) atoms. The Na(1)-O(3) bond length is 2.39 Å. The Na(1)-O(4) bond length is 2.74 Å. There is one shorter (2.40 Å) and one longer (2.53 Å) Na(1)-O(2) bond length. There is one shorter (2.29 Å) and one longer (2.41 Å) Na(1)-O(5) bond length. In the second Na site, Na(2) is bonded in a 7-coordinate geometry to one H(1), one O(1), one O(3), two equivalent O(2), and two equivalent O(5) atoms. The Na(2)-H(1) bond length is 2.54 Å. The Na(2)-O(1) bond length is 2.64 Å. The Na(2)-O(3) bond length is 2.50 Å. There is one shorter (2.40 Å) and one longer (2.41 Å) Na(2)-O(2) bond length. There is one shorter (2.76 Å) and one longer (2.84 Å) Na(2)-O(5) bond length. In the third Na site, Na(3) is bonded to one O(1), one O(5), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(3)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra,  an edgeedge with one P(1)O4 tetrahedra, and  a faceface with one Na(3)O6 octahedra. The corner-sharing octahedral tilt angles are 78°. The Na(3)-O(1) bond length is 2.51 Å. The Na(3)-O(5) bond length is 2.44 Å. There is one shorter (2.43 Å) and one longer (2.48 Å) Na(3)-O(3) bond length. There is one shorter (2.35 Å) and one longer (2.43 Å) Na(3)-O(4) bond length. P(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form PO4 tetrahedra that share corners with three equivalent Na(3)O6 octahedra and  an edgeedge with one Na(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-69°. The P(1)-O(2) bond length is 1.56 Å. The P(1)-O(3) bond length is 1.56 Å. The P(1)-O(4) bond length is 1.56 Å. The P(1)-O(5) bond length is 1.57 Å. H(1) is bonded in a single-bond geometry to one Na(2) and one O(1) atom. The H(1)-O(1) bond length is 1.00 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to two equivalent Na(2), two equivalent Na(3), and two equivalent H(1) atoms. In the second O site, O(2) is bonded to two equivalent Na(1), two equivalent Na(2), and one P(1) atom to form distorted edge-sharing ONa4P square pyramids. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), two equivalent Na(3), and one P(1) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to one Na(1), two equivalent Na(3), and one P(1) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one Na(3), two equivalent Na(1), two equivalent Na(2), and one P(1) atom.