HYDRATES OF WEAK AND STRONG BASES .5. CRYSTAL-STRUCTURES OF KOH.2H2O (SUBSTRUCTURE) AND KOH.4H2O

In the context of studies on formation and structure of base hydrates the crystal structures of KOH . 2H2O and KOH . 4H2O have been determined. For both structures, MoKa diffractometer data were used, obtained at -150-degrees-C, which allowed also the complete set of H atoms to be localized and refined. The dihydrate, melting incongruently at 33-degrees-C, crystallizes with a superstructure. The substructure, which is reported here, is tetragonal with space group 14(1)/amd and Z = 8 formula units per unit cell of dimensions a = 7.154 and c = 13.415 angstrom. With 462 independent observed reflections an R value of 0.026 was obtained. K(H2O)8+ cubes via common faces form rods and these in a tetragonal four-layer packing pattern are further linked into a three-dimensional framework. The OH- ions, hydrogenbonded by the H2O molecules, are located with a twofold disorder in additional cubes of this framework, not occupied by K+ ions. The tetrahydrate, melting congruently at -33.7-degrees-C, is monoclinic with space group P2(1)/c and Z = 4. The unit cell dimensions are a = 6.951, b = 11.530, c = 7.080 angstrom and beta = 99.19-degrees. With 2198 independent observed reflections the final R value is 0.025. Trigonal K(H2O)6+ prisms ascross common edges form layers, which are linked with each other via OH- ions and only loosely cation-bonded H2O molecules.