Structure of silver clusters embedded in erionite channels

Abstract.

The structure of silver clusters stabilised in erionite has been studied by EXAFS, and the results support an interpretation given previously that the absorption peaks at 322 and 293 nm in the optical spectra of the sample belong to the cluster species Ag₈ ⁰ and Ag₈ ^δ+. Five possible geometries were considered for an Ag₈ cluster, and for each one, the expected Ag EXAFS was calculated and compared with the experimental data. The observed coordination numbers indicate an absence of bulk silver metal, and the best fit was obtained for a polyhedron with D_2d symmetry, which corresponds closely with the results of minimum energy structure calculations. The derived Ag-O distances discount the formation of silver oxides, but are consistent with a weak interaction between the silver clusters and the oxygen atoms of the surrounding channel. The results therefore indicate that erionite promotes the formation of 8-atom silver clusters in the channels of the crystalline framework.