Hydrogen bonding. VI. Structural and infrared spectral analysis of lithium hydroxide monohydrate and cesium and rubidium hydroxide hydrates

The infrared spectrum of LiOH.H2O shows, in addition to the stretching and bending modes of OH and H2O groups, seven bands in the 1000 to 300-cm-1 region. Four of these bands give characteristic shifts upon deuterium substitution and confirm the presence of coordinated water and hydroxide ion in LiOH.H2O. On the basis of internal coordinate analysis of the coordinated water and hydroxide subunits of the crystal structure, the various rocking and torsional vibrations of oxygen--hydrogen atoms and the lithium--oxygen lattice vibrations were assigned. Unlike other alkali metal hydroxide hydrates the water and hydroxide ions in LiOH.H2O form discrete, planar, hydrogen-bonded [(OH-)2(H2O)2] anionic units rather than extended chains. RbOH and CsOH also form stable mono- and hemihydrates, the infrared spectra of which contain the rocking and wagging modes of strongly hydrogen-bonded, coordinated water. (auth)