Interaction of tetrameric silver with ammonia in AgCs-rho zeolite

Abstract

Cationic silver clusters formed in γ-irradiated AgCs-rho zeolite have been studied by EPR spectroscopy. Tetrameric silver is formed efficiently in the dehydrated form of zeolite as well as in samples exposed to ammonia. However, the hyperfine splitting of the Ag₄³⁺ pentet in AgCs-rho/NH₃ zeolite is distinctly smaller due to the shift of spin density from silver to nitrogen nuclei, suggesting the formation of an Ag₄³⁺–ammonia complex. The observed ¹⁴N and ¹⁵N superhyperfine splitting from interacting ¹⁴NH₃ and ¹⁵NH₃ molecules unequivocally proved the presence of a multicore Ag₄³⁺(NH₃)_n complex. Based on the simulation of ¹⁴N and ¹⁵N superhyperfine interactions a structure of the complex was proposed in which two ammonia molecules are located close to the octagonal windows of two neighboring α-cages and four further molecules are placed in next-neighboring α-cages interacting with the Ag tetramer through square windows. When dehydrated AgCs-rho zeolite containing radiation-induced Ag₄³⁺ clusters is exposed to ammonia the Ag hyperfine splitting of silver tetramer decreases from 13.9 to 10.7 mT proving that Ag₄³⁺ clusters are located in the sites accessible to adsorbates.