SILVER, SODIUM HALOSODALITES - CLASS-A SODALITES

Class A sodalites of the composition Na8X2(SiAlO4)6 were synthesized hydrothermally (X = Cl-, Br-, I-). AgNO3 melt and hydrothermal aqueous exchanges were used to replace Na+ ions by Ag+ ions. The sodalite precursors and products were studied by chemical analysis, powder XRD, mid- and far-IR, multinuclear MAS- and DOR-NMR and optical reflectance spectroscopy. The structures of selected precursors as well as partially and fully silver exchanged sodalites were determined by Rietveld refinement of high resolution powder X-ray data. The unit cell sizes depended on the type and loading of cation and anion. Combined results from the above techniques indicated that a solid-solution structure of cages with different cation contents was formed. Organized assemblies of Na4-nAgnX3+ clusters consisting of the components of insulators (NaX) and semiconductors (AgX) were encapsulated by the cubic sodalite framework which forms perfectly periodic arrays of all-space filling 6.6 angstrom cages. The concentration and identity of cations and nature of the anion controlled the extent of vibrational and electronic coupling between clusters. Vibrational coupling was strongly mediated by the anions. Electronic interaction was possible through the framework (Na, Ag) or directly (Ag). Extended Huckel molecular orbital calculations supported the idea of band formation for an extended Na4-nAgnX3+ cluster lattice at increasing Ag+ loadings. They also aided in the assignment of the optical spectra. The calculations indicated that electronic transitions existed between clusters and the framework.