STRUCTURE OF FERROELASTIC K3H(SEO4)2

Tripotassium hydrogenbis(selenate), K3H(SeO4)2, M(r) = 404.2, monoclinic, A2/a, a = 10.1291 (8), b = 5.9038 (5), c = 14.961 (1) angstrom, beta = 103.640 (8)-degrees, V = 869.5 (1) angstrom3, Z = 4, D(x) = 3.086 Mg m-3, lambda(Mo Kalpha) = 0.71073 angstrom, mu = 9.86 mm-1, F(000) = 760, T = 299 K, R(F) = 0.0294 for 1670 unique reflections. K3H(SeO4)2 is isomorphous with most M3H(XO4)2-type crystals (M = K, Rb and Cs; X = S and Se); two SeO4 groups are connected by a crystallographically symmetric hydrogen bond into a dimer. The bond distances and angles in the SeO4 group are similar to those in Rb3H(SeO4)2 and Rb3D(SeO4)2. The hydrogen-bond length, 2.524 (5) angstrom, is the shortest among the members of the M3H(SeO4)2 family exhibiting the low-temperature phase transition.