The kinetics and mechanisms of the oxidation of I- and Br- by trans-[Ru-VI(N2O2)(O)(2)](2+) have been investigated in aqueous solutions. The reactions have the following stoichiometry: trans-[Ru-VI(N2O2)(O)(2)](2+) + 3X(-) + 2H(+) -> trans-[Ru-IV(N2O2)(O)(OH2) ](2+) + X3 (X = Br, I). In the oxidation of I- the I-3(-) is produced in two distinct phases. The first phase produces 45% of I-3(-) with the rate law d[I-3(-)]/dt = (K-a + K-b[H+])[Ru-VI]. The remaining I-3(-) is produced in the second phase which is much slower, and it follows first-order kinetics but the rate constant is independent of [I-], [H+], and ionic strength. In the proposed mechanism the first phase involves formation of a charge-transfer complex between Ruvl and I-, which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [Ru-IV(N2O2)(O)(OHI)](2+), and a one electron transfer to give [Ru-V(N2O2)(0)(OH)](2+) and 1(center dot). [Ru-V(N2O2)(O)(OH)](2+) is a stronger oxidant than [Ru-VI(N2O2)(0)2]2+ and will rapidly oxidize another I- to I-center dot. In the second phase the [Ru-IV(N2O2)(O)(OHI)(2+) undergoes rate-limiting aquation to produce HOI which reacts rapidly with I- to produce I-2. In the oxidation of Br- the rate law is -d[Ru-VI]/dt = {(K-a2 + K-b2[H+]) + (K-a3 + k(b3)[H+]) [Br-]}[Ru-VI][Br-]. At 298.0 K and l = 0.1 M, ka2 = (2.03 +/- 0.03) x 10(-2) M-1 s(-1), k(b2) = (1.50 +/- 0.07) x 10(-1) M-2 S-1, k(a3) = (7.22 +/- 2.19) x 10(-1) M-1 s(-1) and k(b3) = (4.85 +/- 0.04) x 10(2) M-3 s(-1). The proposed mechanism involves initial oxygen atom transfer from trans-[Ru-VI(N2O2)(O)(2)](2+) to Br- to give trans-[Ru-IV(N2O2)(O)(OBr)](+), which then undergoes parallel aquation and oxidation of Br, and both reactions are acid-catalyzed.