Infrared and quantitative adsorption study of coordinatively unsaturated cations on magnesium hydroxide

Abstract

Fourier-transform infrared (FTIR) spectroscopy and the quantitative adsorption of water vapour and pyridine have been used to study the dehydration of magnesium hydroxide at temperatures below decomposition and the results have been interpreted in terms of a simple model. The agreement of the quantitative analysis with the predictions of the model implies that equal amounts of three- and five-coordinate Mg²⁺ cations, which behave as only weakly acidic Lewis sites, are present on the edge faces of the crystals. These coordinatively unsaturated ions are intrinisic to the structure and it is therefore unnecessary to postulate morphological or crystallographic defects in order to explain their presence.