A MAGNETIC-RESONANCE STUDY OF THE INCLUSION-COMPOUNDS OF SODIUM IN ZEOLITES - BEYOND THE METAL PARTICLES MODEL

The reaction between sodium vapor and three different zeolites-Na-X, Na-Y, and Na-A-has been studied quantitatively, as a function of the concentration of metal. Its efficacy in introducing sodium into the zeolite pores, selectively and on a large scale, is demonstrated through Na-23 solid-state NMR measurements. The ESR singlet lines, previously thought to originate from metallic clusters within the zeolite pores, have been closely examined to test in some detail the properties of sodium in zeolites against those expected of the smallest metal particles. Although they exhibit g values characteristic of sodium metal, it is clear that these ESR spectra are not consistent with a simple metal particles model, and that talk of quantum size effects in such systems is premature. An alternative conceptual framework for the study of this class of compounds is developed, which focuses on the interaction of (ionized) sodium valence electrons with the zeolite cations, and with each other. The model described is consistent with many aspects of the experimental observations and suggests that such compounds may contribute to our understanding of the metal-nonmetal transition.