Paramagnetic Silver Species in Irradiated Ag-NaA Zeolites. An EPR and ESEEM Study

Several polymeric silver clusters have been observed in Ag(x)-NaA zeolite ( x = 1,6) of varying water content, which was exposed to x-rays at 77 K and annealed at higher temperatures, (109)Ag(1)-NaA zeolite dehydrated at 130 degrees C yields the dimer (109)Ag(2)(+) and the trimer (109)Ag(3)(2+) after irradiation at 77 K and annealing at 240 K. Owing to the use of one Ag isotope the EPR spectra of these species are highly resolved exhibiting g and hyperfine anisotropy. By irradiation of (109)Ag(x)-NaA zeolite (x = 1,6) in hydrated form two new trimeric silver clusters I and II are produced. The ratio between I and II depends on the initial Ag content. ESEEM spectra of these species show interaction with aluminum nuclei of the framework and with distant water molecules. If Ag(6)-NaA zeolite dehydrated at 130 degrees C is irradiated the hexameric cluster Ag(6)(n+) is formed. The ESEEM spectrum shows interaction only to aluminum nuclei. From ESEEM experiments on Ag(6)(n+) with added adsorbates (D(2)O, CD(3)OD) it could be inferred that Ag(6)(n+) is only stable if the neighbouring cages do not contain adsorbate molecules.