Redox reactions in aqueous solutions of PtBr42- and PtBr62-

In aqueous solutions PtBr42- is oxidized by OH to PtBr4OH- and PtBr62- is reduced by eaq- or H to PtBr63-. These Pt(III) species react then with H2O to produce aquobromocomplexes of Pt(III). Kinetics of reactions and properties of intermediate products are described, as studied using the methods of fast spectrophotometry and conductivity. Oxidation of PtBr42- by OH to PtBr4OH2- is fast, k4 = 1.2 x 109 M-1 s-1, similarly as by Br2- to PtBr4-, k5 = 1.3 x 109 M-1 s-1. Reduction of PtBr62- or PtBr5(H2O)- by eaq-, is very fast, the respective rate constants being k6 = 3.3 x 1010 M-1 s-1 and k7 = 2.6 x 1010 M-1s-1. Stability of the intermediate PtBr63- is larger than that of the analogous PtCl63-, the bromide complex exchanging in aqueous solution only one Br- for OH- in comparison to two Cl- in the case of chloride. (author)