Charge transfer initiated nitroxyl chemistry on free silver clusters Ag2–5−: Size effects and magic complexes

The reactivity of small silver cluster anions Ag2–5− toward nitric oxide and mixtures of nitric oxide with carbon monoxide is investigated under multi-collision conditions in a radio frequency octopole ion trap at temperatures of 100 and 300 K. A strongly cluster size dependent reaction behavior is observed, where reactive fragmentation dominates for clusters with four or fewer atoms and only Ag5− is able to form reaction products without dissociation of the metal cluster. The decisive role of charge transfer in the NO bond breakage, NO oxidation, and the formation of free NO2− and N2O4− ions, as well as NxO(y>x)-ligands on the silver clusters is discussed. The mass spectrometric data reveal the particular stability of the reaction products AgN2O4− and Ag3NO−. The reaction product mass spectra obtained for Ag5− in the presence of NO and CO show the depletion of the NxO(y>x)-ligands on the metal cluster possibly involving the oxidation of CO to CO2.