Complexation of a nickel(III) macrocyclic complex by sulfate ion. A pulse radiolytic study

Abstract

The kinetics of oxidation of Ni11[meso-Me6[14]aneN4] (NiL2+) to Ni(III) by OH radical and subsequent complexation by sulfate ion have been studied in acidic aqueous media at 22°C and μ=0.01-0.3 M by the pulse radiolytic technique. Results indicate that NiL3+hydrolyzes with a pK+3.7±0.2 but that, at least up to pH 5.2, substitution by SO42- occurs only on the unhydrolyzed species with a rate constant of 1X106 M-1 s-1 at μ=0.03 M. The equilibrium constant for sulfate complexation is 3.0X104 M-1 at μ=0.03 M and the product of the reaction is identical with the stable NiLSO4+species produced by the electrochemical oxidation of NiL2+in sulfate media. The results demonstrate the stabilization of NiIII by sulfate complexation. © 1979, American Chemical Society. All rights reserved.