Effects of added potassium bromide and tetra-n-butylammonium bromide on the kinetics of aquation of tris(5-nitro-1,10-phenanthroline)iron(II) in various binary aqueous mixtures

Abstract

Rate constants are reported for the aquation of the title complex [Fe(5NO₂-phen)₃]²⁺ in a series of binary aqueous mixtures at 298.1 K as a function of the concentration of added KBr or [NBu₄]Br. The co-solvents are acetone, dimethyl sulphoxide, acetonitrile, and t-butyl alcohol. In each system the first-order rate constant increases when [NBu₄] Br is added but decreases when KBr is added. The results are used to show that salt effects on this reaction are determined to a large extent by the size of the ion, although certain changes in the pattern of kinetic data particularly for t-butyl alcohol mixtures show that hydration and solvation interactions play some part in determining the overall trend.