“…For Na 2 SeO 3 , the anhydrous form (P2 1 /c, Z = 4) is made up from [NaO 6 ] octahedra and trigonal-pyramidal SeO 3 2À anions (Wickleder, 2002), and is isotypic with Na 2 TeO 3 (Masse et al, 1980). Hydrated forms are known only for the pentahydrates Na 2 SeO 3 (H 2 O) 5 (Mereiter, 2013) and Na 2 TeO 3 (H 2 O) 5 (Philippot et al, 1979) that are, surprisingly, not isotypic (Pbcm, with Z = 8, and C2/c, with Z = 8, respectively). These structures are based on two-or three-dimensional assemblies of [NaO 5 ] polyhedra (Se) and [NaO 6 ] octahedra (Se and Te), to which SeO 3 /TeO 3 groups are bonded via two (Se) or one (Te) O atom.…”