Intracrystalline Free Volumes in some Host Lattices

Abstract

VARIOUS instances are known of continuous crystalline ‘host’ lattices within which ‘guest’ molecules may be trapped^1,2. Organic lattices of this kind include the networks formed by hydrogen-bonded quinol molecules in the quinol clathrates; hydrogen-bonded urea and thio-urea networks in the urea and thio-urea adducts. Among inorganic lattices the best known are the crystalline zeolites, the most open of which, faujasite, easily occludes molecules as large as iso-octane; and two different kinds of hydrogen-bonded watter lattice, each with cavities able to encage diverse molecular species. It is of interest to compare aspects of the geometry of the free volumes of these host lattices, and to contract the free volumes of the organic and the inorganic lattices. It is also interesting to know the upper limit to the free volume in such continuous networks. Accordingly, the spatial properties of some cage and channel systems are summarized in Table 1. The term ‘free’, used above and in Table 1 in relation to channel and cage dimensions, means not occupied even by the periphery of any of the atoms forming the continuous network.