Base hydrolysis of acidopentaaminecobalt(III) ions and the question of common intermediates. Hydrolysis of some t-[Co(tren)(NH₃)X]^2+/3+ ions (X = NO₃^-, MeSO₃^-, Cl^-, Me₂SO, N₃^-)

Abstract

The preparations, and characterizations, of the complex cations t-[Co(tren)(NH₃)X]^2+/3+* (X = NO₃^-, Me₂SO, H₂O, Cl^-, N₃^-) and p-[Co(tren)(NH₃)X]^2+/3+ (X = N₃^-, Cl^-, H₂O) are described. Base hydrolysis of t-[Co(tren)(NH₃)X]^2+/3+ (X = MeSO₃^-, Me₂SO, NO₃^-, N₃^-) and of p- [Co(tren)(NH₃)N₃]²⁺ follows the rate law k_obs = k[OH^-] over the [OH^-] range 1.0-10^-4 mol dm^-3 except for the 3+ ion t-[Co(tren)(NH₃)Me₂SO]³⁺ where some curvature is observed at [OH^-] > 0.025 mol dm^-3. The products for the t-[Co(tren)(NH₃)X]^2+/3+ ions (X = Cl^-, NO₃^-, MeSO₃^-, Me₂SO) depend on X, and on the presence or absence of supporting electrolyte (1.0 mol dm^-3 NaClO₄ or NaN₃) varying from 12.1 % retention of the t-configuration for X = NO₃^- in the absence of electrolyte to c. 26% for X = Me₂SO in 1.0 mol dm^-3 NaN₃. Significantly more retention is observed in the azido products (75-80% t-[Co(tren)(NH₃)N₃]²⁺). The results are interpreted in terms of important contributions to the mechanism from pre-formed ion pairs.