Flexibility and Cation Distribution upon Lithium Exchange of Aluminosilicate and Aluminogermanate Materials with the RHO Topology

Abstract

The influence of lithium substitution on the structure of aluminosilicate (AlSi) and aluminogermanate (AlGe) materials with the zeolite RHO topology has been examined. The exchanged materials were dehydrated and structurally characterized via Rietveld refinement using neutron powder diffraction data. Li−AlSi-rho crystallizes in the space group I43m with a = 14.2609(3) A, whereas Li−AlGe−rho adopts the space group I23 with a = 14.2926(5) A. The extraframework cations reside in their expected positions in Li−AlSi-rho: cesium is found in the double eight ring (D8R) and lithium is observed only in the single six ring (S6R). In Li−AlGe-rho, lithium resides in both the single six ring and the single eight rings (S8R) while cesium is located exclusively in the S6R. Although these cation positions are unusual for materials with the RHO topology, they are a response to the framework distortions introduced by ion exchange and dehydration. The extraframework cation positions correspond to those that best satisfy t...