Redox Kinetics of Carbonyl Platinum Clusters Studied by Pulse Radiolysis

摘要

The pulse radiolysis method allows the direct investigation for the first time of the reduction mechanism of carbonyl platinum clusters and the determination of the reaction steps and kinetics involved in the process. These time-resolved observations demonstrate that the reduction process of [Pt_3(CO)_6]_n~(2-) clusters starts by a monoelectronic reduction initiated by alcohol radicals and yields [Pt_3(CO)_6]_n~(3-). These species are unstable and dimerise into [Pt_3(CO)_6]_(2n)~(6-) with a diffusion-controlled rate. Then, the dimers [Pt_3(CO)_6]_(2n)~(6-) immediately split to develop stable [Pt_3(CO)_6]_4~(2-) and, in the case of n = 7-9, additional unstable [Pt_3(CO)_6]_(n-4)~- clusters. As a general observation, we also found that the mono- or triply charged clusters have the same absorption spectra as the stable doubly charged clusters of which they are the transient oxidised and reduced form, respectively. The pulse radiolysis study provides at longer times the observation of the kinetics of the reaction occurring between two nonconsecutive oligomers, which is a consequence of the redox potential increase with the nuclearity.