Formation and characterization of transitory platinum–ammonia complex ions using pulse radiolysis

The reactions of tetraammineplatinum(II) complex ion with the hydrated electron and hydrogen atom have been investigated in aqueous media using the technique of pulse radiolysis coupled with absorption and conductivity detection. Analysis has also been carried on pulse-irradiated solutions for the formation of free ammonia and for changes in concentration of Pt(II). The hydrated electron and hydrogen atom react with the complex at near diffusion-controlled rates, with the respective rate constant being 1.9 ± 0.1 × 1010 M−1 s−1 and 2.8 ± 0.3 × 1010 M−1 s−1. The nascent products of these reactions are shown to be different transitory species. For the electron reaction, the initial product is Pt(NH3)4+ in which the metal center is formally Pt(I). In acidic media, there is a subsequent and rapid release of two ammonia ligands, with only the second step being measurable (k = 4.2 ± 1.7 × 104 s−1). In the reaction of H atom, the results support the occurrence of an addition process, giving rise to a hydrido type product. This species undergoes a first-order reaction (k = 2.2 ± 0.6 × 104 s−1); however the process is not associated with a change in conductivity, and thus it is not one involving loss of ammonia. Subsequent to this process, the loss of one ammonia ligand is observed, with k = 2.0 ± 0.6 × 103 s−1. The natures of these transients and the long term behavior of these systems are discussed.