HYDRATES OF WEAK AND STRONG BASES .7. CONCERNING THE SYSTEM CESIUM HYDROXIDE WATER - THE CRYSTAL-STRUCTURES OF CSOH . 2H2O AND CSOH . 3H2O

In the context of structural studies of hydrates of the alkali metal hydroxides the crystal structures of CsOH . 2 H2O and CsOH . 3 H2O have been determined for the first time. The diffractometer data, obtained at -150-degrees-C, made it possible to locate and refine also all the H-atoms. The dihydrate was found to probably form only one phase, melting incongruently at 2,5-degrees-C. It is orthorhombic with space group Pca2(1) and Z = 8 formula units per unit cell. The lattice constants are a = 13.238, b = 6.747 and c = 9.121 angstrom. With 1870 independent observed reflections a final R value of 0.013 was obtained. The trihydrate, melting congruently at -5.5-degrees-C, is monoclinic with space group P2(1)/n, Z = 4 and lattice constants a = 8.637, b = 5.984, c = 10.061 angstrom and beta = 96.57-degrees. With 2098 independent observed reflections the final R is 0.026. In both hydrate structures there are no simple characteristic coordination polyhedra for the cations; in each case it is rather the hydrogen-bonded and fully ordered anionic water structure which shows up as the determining building principle. Both these water structures are altogether three-dimensional, but primarily contain layers. The anionic layers are formed by condensation of small and medium rings, namely four-, five- and seven-membered rings in CsOH . 2 H2O and four-, five- and six-membered ones in CsOH . 3 H2O. They are linked together by one set each of extra H2O molecules between the layers as well as by the Cs+ ions.