Kinetic Study of the Acid-catalysed Hydrolysis of Cobalt(III) Carbonato Complexes with Nonlabile Tetrakis(methylamine), Tetrakis(ethylamine), Fac ( N )-(ethylenediamine)(glycinato), Mer ( N )-(ethylenediamine) (glycinato) or Bis(1,3-propanediamine) Ligands

Abstract

Acid-catalysed hydrolysis kinetics were studied for 14 cobalt(III) carbonato complexes involving the title five at oxonium ion concentration of 0.01-1.0 M, ionic strength of 2.0 (NaClO 4 ) and 15-45°C (M=mol dm m 3 ). Preprotonation constant, about 1 M m 1 , was estimated from a non-linear acidity dependence of an experimental rate constant for the ring-opening of the didentate hydrogencarbonato intermediate. Acidity constant, 0.003-0.7 M, and basicity constant, 0.1-0.9 M m 1 , of the ring-opened aquahydrogencarbonato intermediate were estimated from an acidity dependence of an experimental rate constant for the decarboxylation. Concerning the widely ranging ring-opening rate constants (0.05-126 s m 1 at 25°C), we demonstrate labilizing effects of a reduced charge and of small tetrakis(amine) ligand, correlating with a high activation entropy, as well as of the trans five-membered chelate correlating with a low activation energy. The charge effect may be understood by the solvational change during the dis...