Crystal structures of Na(2)SeO(4)·1.5H(2)O and Na(2)SeO(4)·10H(2)O

The crystal structures of Na(2)SeO(4)·1.5H(2)O (sodium selenate sesquihydrate) and Na(2)SeO(4)·10H(2)O (sodium selenate deca­hydrate) are isotypic with those of Na(2)CrO(4)·1.5H(2)O and Na(2) XSeO(4)·10H(2)O (X = S, Cr), respectively. The asymmetric unit of the sesquihydrate contains two Na(+) cations, one SeO(4) tetra­hedron and one and a half water mol­ecules, the other half being generated by twofold rotation symmetry. The coordination polyhedra of the cations are a distorted monocapped octa­hedron and a square pyramid; these [NaO(x)] polyhedra are linked through common edges and corners into a three-dimensional framework structure, the voids of which are filled with the Se atoms of the SeO(4) tetra­hedra. The structure is consolidated by O—H⋯O hydrogen bonds between coordinating water mol­ecules and framework O atoms. The asymmetric unit of the deca­hydrate consists of two Na(+) cations, one SeO(4) tetra­hedron and ten water mol­ecules. Both Na(+) cations are octa­hedrally surrounded by water mol­ecules and by edge-sharing condensed into zigzag chains extending parallel to [001]. The SeO(4) tetra­hedra and two uncoordinating water mol­ecules are situated between the chains and are connected to the chains through an intricate network of medium-strength O—H⋯O hydrogen bonds.