Positions of cations and molecules in zeolites with the faujasite-type framework III hydrated Ca-exchanged faujasite

Abstract

Only one-third of the electron density of the non-framework atoms was located in hydrated Ca-exchanged faujasite at room temperature. The electron density in the super-cage is mostly smeared out, as expected from other evidence for rapid movement of water molecules. Well-defined peaks at S(I′) and S(II′) are explained most simply by Ca in S(I′) bonded to O(3) and to H 2O in S(II′), but other arrangements are possible. A peak at S(V) probably, and a peak at S(II∗) may, represent hydrated Ca ions. The wide dispersion of ions and molecules explains why the aluminosilicate framework is more regular than in the dehydrated form. The terms “liquid” and “brine” are too simple for the complex variation of bonding between ions and molecules.