Crystal structures of the hydrated and partially dehydrated forms of CdX exchanged zeolites

Abstract

Single-crystal structures of the hydrated, ( hCdX), and partially dehydrated, ( pdCdX) CdX zeolites are reported. For the cubic space group Fd 3 , the unit cell parameter is a=24.797(5) A ̊ ( hCdX) with the unit cell content Cd 44Al 88Si 104O 384·233H 2O and a=24.818(5) A ̊ ( pdCdX) with the unit cell content Cd 44Al 88Si 104O 384·138H 2O. Refinements were carried out using 661 and 348 independent reflections with l>2σ( l), respectively, and gave final R values of 0.082 ( hCdX) and 0.088 ( pdCdX). In hCdX the Cd 2+ ions are located in two sites of high occupancy along the triad axis, one in the sodalite cage (site I′), the other near the walls of the ε cage (site II). A third site of low occupancy was assigned to Cd 2+ in the large cage (site IIIA). Partial dehydration causes some cations to move from these sites to site I in the middle of the D6R unit and to site II ∗ along the triad axis in the middle of the six-membered rings connecting the sodalite and the ε cages. No significant changes in the framework structure are observed. Dehydration results in a lowering of the coordination number of Cd 2+ and a decrease of water content, mainly in the large cavity.