Aspects of the adsorption of aurocyanide anions Au(CN) 2 − onto an activated carbon from alkaline media and the effects of subsequent acid reaction have been examined using X-ray photoelectron spectroscopy (XPS). The results indicate that the linear Au(CN) 2 − anion adsorbed intact on and parallel to the graphitic planes of the carbon, with the graphitic π-electrons taking part in a donor bond to the central gold atom, stabilized by charge transfer to the terminal nitrogen atoms. This bonding mechanism was maintained after acid reaction induced oligomerization of the adsorbed Au(CN) 2 − producing the tetramer Au 4 (CN) 5 − which attached to the graphitic plane via four identical π-donor bonds. These additional bonds necessitated the terminal nitrogen atoms to accept even further charge transfer so as to accommodate the larger carbon-anion complex.
