Synthesis and crystal structure of sodium hydrogen selenates, NaHSeO4 and Na-3[H(HSeO4)(2)](HSeO4)(2)

Sodium hydrogen selenates of the compositions NaHSeO4 (I) and Na-3[H(HSeO4) (2)](HSeO4)(2) (II) have been crystallized in the Na2SeO4-H2SeO4-H2O system at the H2SeO4 concentrations similar to 70 and similar to 80%, respectivel y. Sodium atoms in the structures of compounds I and II are surrounded by o xygen atoms forming distorted octahedra. The Se-O distances in the tetrahed ral SeO4 groups range within 1.60-1.73 Angstrom depending on the additional structural functions performed by O atoms (hydrogen donors or accepters, o xygen coordination with metal). The system of hydrogen bonds in compound I is represented by closed (HSeO4)(2) dimers. The structure of compound II co nsists of infinite chains of two types of dimers bound by hydrogen bonds-(H SeO4)(2) and [H(HSeO4)(2)].