MIXED-METAL CLUSTERS IN AQUEOUS-SOLUTION - REACTIONS OF CD+, CO+, ZN+, AND NI+ WITH AG+

Various monovalent cations, such as Cd+, Co+, Zn+, and Ni+, are pulse radiolytically generated in aqueous solutions of the corresponding bivalent metal ions, which also contain Ag+ ions in low concentration. Zn+, which has a high negative electrochemical potential, reacts with Ag+ via electron transfer to yield the free silver atom. Cd+ and Co+, which have less reducing power, form the respective clusters (CdAg)(2+) and (CoAg)(2+) with rate constants of the order of 10(9) M(-1) s(-1). It is concluded that the electrochemical potentials of the redox couples Cd2+/Cd+, Co2+/Co+, and Ag+/Ag-0 (Ag-0 is a free silver atom) lie close together. The mixed metal dusters live only for microseconds as they rapidly react with excess silver ions to yield Cd2+ (or Co2+) and Ag-2(+). AS cluster formation and reoxidation occur in the same time range, computer simulations are applied to obtain the rate constants and the absorption spectra of the clusters. (CdAg)(2+) absorbs at 270 and 300 nm; (CoAg)(2+) absorbs at 310 and 550 nm. Neither does Ni+ transfer an electron to Ag+ nor is a cluster formed; however, reduction of Ag+ can occur by products that are formed when the Ni+ ions disappear.