Crystals of two new polymorphic forms of the known compound (NaCl)[Cu(HSeO3)2], which we term polymorphs II and III, were formed after a ca. one-year dwelling of a crystalline precipitate under mother liquor and upon crystallization in the presence of K+, respectively. Both structures belong to the “layered copper hydroselenite” family. The polymorph II is a structural analog of (KCl)[Cu(HSeO3)2] with a fully ordered Na+ site; the main difference concerns the environment of Cu2+ which is more regular in (NaCl)[Cu(HSeO3)2]-II. In contrast to some expectations, crystallization from solutions containing KCl. NaCl, CuCl2, and H2SeO3 upon evaporation does not result in formation of mixed (Na1−x K x Cl)[Cu(HSeO3)2] crystals, but rather in a separate crystallization of (KCl)[Cu(HSeO3)2] and (NaCl)[Cu(HSeO3)2]-III which exhibits a complex structure with four ordered and one disordered Na+ sites. It is possible that longer crystallization times enhance formation of ordered structures.

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Singe crystals of four new A I M II[ReO4]3 perrhenates (A I = Na, M II = Pb; A I = Na, M II = Sr, Ag, K) have been prepared from the respective A I[ReO4] and M II[ReO4]2 perrhenates using melt and solution evaporation techniques. All new compounds belong to the hexagonal CdTh[MoO4]3 structure type, similar to previously known NaCa[ReO4]3. We discuss the crystal chemical relationships within this structure type and suggest existence of some more representatives involving other tetrahedral anions.

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