Sodium selenite penta­hydrate, Na(2)SeO(3)·5H(2)O

In the crystal structure of Na(2)SeO(3)·5H(2)O [disodium selen­ate(IV) penta­hydrate], two Se, two selenite O atoms and one water O atom are located on a mirror plane, and one water O atom is located on a twofold rotation axis. The coordination of one Na(+) cation is distorted trigonal bipyramidal, formed by three equatorial H(2)O ligands and two axial selenite O atoms. The other Na(+) cation has an octa­hedral coordination by six water mol­ecules. The two independent SeO(3) groups form almost undistorted trigonal pyramids, with Se—O bond lengths in the range 1.6856 (7)–1.7202 (10) Å and O—Se—O angles in the range 101.98 (3)–103.11 (5)°, and both are μ(2)-O:O-bonded to a pair of Na(+) cations. Hydrogen bonds involving all water molecules and selenite O atoms consolidate the crystal packing. Although anhydrous Na(2)SeO(3) and Na(2)TeO(3) are isotypic, the title compound is surprisingly not isotypic with Na(2)TeO(3)·5H(2)O. In the tellurite hydrate, all Na(+) cations have an octa­hedral coordination and the TeO(3) groups are bonded to Na(+) only via one of their three O atoms.