Effect of solvent and structure on the kinetics and mechanism of the aquation of bromopentaamine cobalt(III) complex in binary aqueous mixtures

Abstract

AbstractThe kinetics of aquation of bromopentaamine cobalt(III) complex have been investigated spectrophotometrically in aqueous‐organic solvent media using acetonitrile, urea, and dimethyl sulfoxide as co‐solvents at 45 ≤ T (°C) ≤ 65. The logarithms of rate constant of the aquation reaction vary nonlinearly with the reciprocal of the dielectric constant for all cosolvent mixtures, indicating a specific solute–solvent interaction. Also, the rate constants are correlated with the total number of moles of water and the organic solvents. However, the solvent effects on the solvation components of the enthalpy of activation, ΔH‡, and the entropy of activation, ΔS‡, have been studied. Analysis of the solvent effect confirmed a common Id mechanism for the aquation of the cobalt(III) complex. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:494–499, 2004