The crystal structures of Hg7Se3O13H2 and Hg8Se4O17H2 — two mixed-valent mercury oxoselenium compounds with a multifarious crystal chemistry

Single crystals of the mixed-valent compounds Hg7Se3O13H2 (I) and Hg8Se4O17H2 (II) were grown under hydrothermal conditions. The crystal structures were solved and refined from single crystal X-ray data collected at room temperature (I: R3, Z = 3, a = 5.9239(3), c = 37.096(3) Å, 1465 structure factors, 60 parameters, R[F 2 > 2σ(F 2)] = 0.0383, wR(F 2 all) = 0.0970, Goof = 1.047; II: P31c, Z = 2, a = 5.8908(6), c = 31.048(3) Å, 1889 structure factors, 69 parameters, R[F 2 > 2σ(F 2)] = 0.0662, wR(F 2 all) = 0.1626, Goof = 1.088). Both compounds show a multifarious crystal chemistry and contain triangular Hg3 4+ cluster cations, Hg2 2+ dumbbells, Hg2+ cations, HgO2 2– mercurate groups, and trigonal-pyramidal SeO3 2– as well as tetrahedral SeO4 2– anions and water molecules as simple building units. The description in terms of crystal chemistry leads to the more detailed formulae (HgIV/3 3) (HgI 2)(HgII)(HgIIO2)(SeIVO3)2(SeVIO4)(H2O) for I and (HgIV/3 3)(HgI 2)(HgII)2(HgIIO2)(SeIVO3)2(SeVIO4)2(H2O) for II, respectively. Characteristic features of the closely related structures are building blocks formed by parallel layers of Hg3 4+ triangles, layers of disordered Hg2 2+ dumbbells, layers of SeO4 2– and HgO2 2– groups, and layers of SeO3 2– groups which are all stacked along [001]. The layers are linked into a complex three-dimensional framework via common O atoms and H2O molecules. In comparison with Hg7Se3O13H2, the structure of Hg8Se4O17H2 contains an additional and disordered HgSeO4 layer which leads to a significant distortion of parts of the resulting structure.