Interlayer complexes in layer silicates. The structure of water in lamellar ionic solutions

Abstract

The stretching vibrations of water (H₂O, HDO and D₂O) in montmorillonite, hectorite, saponite and vermiculite are split into two components, similar to those seen in perchlorate solutions. Examination of lower hydrates and pyridine complexes of the layer silicates shows that the higher frequency component corresponds to hydrogen bonds to oxygens of Si—O—Si linkages, the lower frequency component to water-water bonds and hydrogen bonds to oxygens of Al—O—Si linkages. The observations are explained in terms of chains of hydrogen-bonded water molecules which form dielectric links between interlayer cations and oxygens on the silicate anion surface. This concept, together with information obtained on the distribution of charge on the surface oxygens, provides a qualitative explanation of the hydration properties of layer silicates, and is extended to account for the stability of organic complexes of montmorillonite and hectorite. Some analogies between interlayer complexes and ionic solutions are proposed.