Crystal structure of hydroxohafnates Na2Hf(OH)(6) and K2Hf(OH)(6)

X-ray study of Na2Hf(OH)(6) (I) and K2Hf(OH)(6) (II) single crystals have b een performed. In the rhombohedral structure of compound I, Hf and Na atoms possess the distorted octahedral coordination with the distances: Hf-O 2.0 8 Angstrom and Na-O 2.42-2.45 Angstrom. In the orthorhombic structure of co mpound II, there are two types of distorted octahedra-HfO6 (Hf-O 2.06-2.09 Angstrom) and eight-vertex KO8-polyhedra (K-O 2.75-3.17 Angstrom). The HfO6 -octahedra are bound by a system of hydrogen bonds with the O ... O distanc es ranging within 2.80-2.85 Angstrom. The results of indexing of the powder diffraction patterns of compounds I and II are also given.