In the three previous papers of this series the role played by the exchangeable cations in the adsorption of methanol by homoionic montmorillonites has been investigated by different techniques, namely desorption isotherms, X-ray determination of the basal spacings and IR spectroscopy. In this last paper, models based on the previous discussions are presented. In the adsorbed state, methanol shows a strong tendency to form on the clay surface, hydrogen-bonded zig-zag chains analogous to those in crystalline CH3OH. The exchangeable cations perturb this arrangement to different extents. For Li+ the perturbation is negligible, for Ca2+ a complete rearrangement is observed and for Na+ and Ba2+ the chains are broken into smaller fragments.