THE DENSITY OF SILICON-RICH ZEOLITE FRAMEWORKS

Many low-density frameworks containing channel networks (such as zeolites) are related to periodic minimal surfaces of well characterized surface area. This observation allows a direct connection to be made between the framework density and the average size of rings in the framework that lie on the hyperbolic surface. The analysis exploits the observation that the area per vertex on the surfaces is the same as that for related uncurved sheet silicates, which implies that the density of the framework can be inferred from the average ring size alone. The relation between density and bond lengths and angles is also discussed. A lower bound for the density of open-framework silicates and hydrophobic zeolites is suggested that is consistent with the preferred bonding geometry of SiO2 networks.