Packing of adsorbed molecules in microporous polymorphs aluminium methylphosphonates alpha and beta

The adsorption of N-2 and CO2 in the microporous aluminium methylphosphonate polymorphs alpha and beta is investigated by adsorption experiments in combination with Monte Carlo (MC) simulations. We find that close steric matching of N-2 and polymorph a causes a packing transition not observed for the other pairs of adsorbate and adsorbent. This strong effect on adsorption behaviour of small differences in the adsorbent structure and adsorbent - adsorbate interactions suggests that microporous, hybrid inorganic - organic materials of this type offer opportunities for highly selective adsorptive separations. The realism of the MC simulations is extraordinarily dependent upon the molecular size parameters used.