Reduction of Ag+ in Aqueous Polyanion Solution: Some Properties and Reactions of Long‐Lived Oligomeric Silver Clusters and Metallic Silver Particles

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AbstractRadiolytic reduction of AgClO4 solutions containing a polyanion leads to the formation of long‐lived oligomeric silver clusters which are stabilized on the polymer chains. Under suitable conditions, the accompanying formation of colloidal silver consisting of metallic particles is strongly suppressed and cluster concentrations of several 10−4 M can be produced. In the presence of polyacrylate, the clusters are particularly long‐lived; they have absorption bands at 300 nm, 340 nm, and 370 nm. The bands of the latter two clusters are red‐shifted as compared to the bands of the unstabilized clusters or clusters stabilized by polyphosphate. The Ag24+ cluster, which is formed in the initial stages of Ag+ reduction, absorbs at 275 and 480 nm in the presence of polyacrylate. – The various clusters react at different rates with electron acceptors, such as oxygen, carbon tetrachloride and nitromethane. The clusters also react with complexing agents, such as ammonia, cyanide and hydrogen sulfide anions, to form larger particles of silver and/or larger complexed clusters. The great reactivity of the clusters towards nucleophilic reagents is explained by the high coordinative unsaturation of the silver atoms in the clusters. This also explains the stabilization of the clusters by the anion groups of the polymers used. – These reactivity studies were also complemented by investigating the reactions of larger silver particles, which already have metallic properties, with complexing agents. The oxidative corrosion of such particles is strongly accelerated by the complexing agents. A mechanism for the catalysis of the oxidative corrosion is presented, in which the principle steps are the complexation of silver atoms on the surface with simultaneous electron transfer into the metal interior (“pre‐complexation” or “pre‐oxidation” of surface atoms) followed by pick‐up of the electrons by oxygen.