KCl72H 2SeO 3 and CsCl7H 2SeO 3 have been synthesized using solution evaporation methods from aqueous solution. Both compounds are monoclinic ( P2/ n and P2 1/ c) and demonstrate new structure types. One symmetrically unique SeO(OH) 2 molecule is present in each structure. SeO(OH) 2 molecules via strong hydrogen bonds form chains in KCl72H 2SeO 3 and layers in ?sCl7H 2SeO 3. The structures of KCl72H 2SeO 3 and CsCl7H 2SeO 3 can be described as consisting of ionic KCl chains and CsCl layers incorporated into the covalent- and hydrogen-bonded H 2SeO 3 matrix. To the best of our knowledge, the cases when selenious acid acts as a contributor to the molecular building blocks of salt-inclusion structures are not known to date.