ON THE TEMPLATING OF CURVATURE IN ZEOLITES

The cage and tunnel descriptions of some zeolite crystal structures have previously been shown to be succinctly described as structural networks lying on periodic minimal surfaces, which are saddle-shaped surfaces whose average curvature vanishes everywhere on the surface. We establish here that the vanishing average curvature of these structures is due to the templating effect of typical cations (e.g., tetraalkylammonium ions) used to synthesize the zeolites. These cations form large hydrated spheres in solution. Given that these ions are locally ordered, the optimal locations for the silicon- and aluminum-containing solvated species are on surfaces of vanishing average curvature which lie between the hydrated cations. Upon crystallization, the average curvature of the aluminosilicate network is frozen in, forming periodic minimal surfaces. This model is applied to the synthesis of the zeolites sodalite, synthetic gismondine, and silicalite I. © 1990, American Chemical Society. All rights reserved.