Published online by Cambridge University Press: 15 February 2011
Voltammetric studies of Au55(PPh3)12Cl6 (kindly provided by Prof. G. Schmid, Essen, Germany) in solutions of CH2Cl2 and THF with Pt electrodes show that the reduction of the cluster is a multistep, irreversible process. Precipitation of colloidal metal or any high molecular super-cluster is observed when stabilising. NBu+ –ions are absent and when the reduced solution is reoxidised.
The parent cluster and the precipitate were studied by X-ray powder diffraction and UV-vis spectroscopy. The origin of the diffuse lines and the low-angle diffractions will be discussed. They suggest that the Au55 particles flocculate by changing their electric charge in the electrochemical redox reactions. The floc is unstable and congulates to particles of 25 Å and larger.