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.