Sodium selenite pentahydrate, Na₂SeO₃·5H₂O

Abstract

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.