Na2SO9 crystallizes in the tetragonal P4_322 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a 2-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. S(1) is bonded in a distorted see-saw-like geometry to two equivalent O(1) and two equivalent O(4) atoms. There are five inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one S(1) atom. In the second O site, O(5) is bonded in a distorted water-like geometry to one Na(2) and one O(2) atom. In the third O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent S(1) atoms. In the fourth O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(5) atom. In the fifth O site, O(3) is bonded in a distorted L-shaped geometry to one Na(2) and one O(3) atom.
Na2SO9 crystallizes in the tetragonal P4_322 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(4) atoms. Both Na(1)-O(2) bond lengths are 2.47 Å. There are two shorter (2.37 Å) and two longer (2.46 Å) Na(1)-O(4) bond lengths. In the second Na site, Na(2) is bonded in a 2-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms. Both Na(2)-O(2) bond lengths are 2.80 Å. Both Na(2)-O(3) bond lengths are 2.53 Å. Both Na(2)-O(5) bond lengths are 2.34 Å. S(1) is bonded in a distorted see-saw-like geometry to two equivalent O(1) and two equivalent O(4) atoms. Both S(1)-O(1) bond lengths are 2.02 Å. Both S(1)-O(4) bond lengths are 1.49 Å. There are five inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one S(1) atom. In the second O site, O(5) is bonded in a distorted water-like geometry to one Na(2) and one O(2) atom. The O(5)-O(2) bond length is 1.28 Å. In the third O site, O(1) is bonded in a bent 120 degrees geometry to two equivalent S(1) atoms. In the fourth O site, O(2) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(5) atom. In the fifth O site, O(3) is bonded in a distorted L-shaped geometry to one Na(2) and one O(3) atom. The O(3)-O(3) bond length is 1.24 Å.