An Ag‐Atom in the 6‐6 Subunit of a Zeolite: Model Calculations

Self‐sensitisation of photo‐oxygen evolution occurs in aqueous dispersions of silver zeolites. In presence of Cl−, chlorine is the photoproduct in acidic medium, and the same type of self‐sensitisation occurs. Self‐sensitisation means that systems which are first insensitive to light of a certain wavelength become photo‐active after they have been illuminated by light of higher energy. For a better understanding of silver zeolites, we have carried out EH‐MO calculations on the 6–6 subunit (SBU) of a zeolite, on the 6–6 SBU with an Ag‐atom in the center, on the 6–6 SBU with one Ag‐atom in the center and one outside on top of the hexagon, and finally on another with one Ag‐atom in the center and two Ag‐atoms outside, each on top of a hexagon. The Ag0 in the cage of the 6–6 SBU is significantly polarized by the 6–6 SBU environment. The energy barrier to escape the 6–6 SBU is 0.8 eV for Ag0 and 0.5 eV for Ag+. The HOMO of the Ag(6–6 SBU) is a totally symmetric 5s* orbital and the LUMO is a 5pz* type. 5pz*←5s* electronic excitation reduces the energy barrier and allows an (Ag0)* to exit the 6–6 SBU, provided the excited‐state lifetime is long enough. The MO picture predicts low‐energy charge‐transfer transitions from the zeolite framework to the 5s* orbital. The highest occupied orbitals of the zeolite framework are localized on the O‐atoms. Interactions between an Ag‐atom in the 6–6 SBU and one or two external Ag‐atoms are discussed.