Mechanism of Trivalent Gold Reduction and Reactivity of Transient Divalent and Monovalent Gold Ions Studied by Gamma and Pulse Radiolysis

The detailed kinetics of the multistep mechanism of the Au-III ion reduction into gold clusters have been investigated by radiation chemistry methods in 2-propanol. In particular, a discussion on the steady state radiolysis dose-dependence of the yields concludes to a comproportionation reaction of nascent gold atoms Au-0 with excess Au-III ions into Au-II and Au-I. This reaction should be achieved through Au-III consumption before the coalescence of atoms Au-0 into gold clusters may occur. Then gold clusters catalyze the reduction of Au-I by 2-propanol. It was also found that a long-lived Au-II dimer, (Au-II)(2), was transiently formed according to the quantitative analysis of time-resolved absorbance signals obtained by pulse radiolysis. Then the disproportionation of Au-II is intramolecular in the dimer instead of intermolecular, as usually reported. The yields, reaction rate constants, time-resolved spectra, and molar extinction coefficients are reported for the successive one-electron reduction steps, involving especially the transient species, such as Au-II, (Au-II)(2), and Au-I. The processes are discussed in comparison with other solvents and other metal ions.