Kinetics and mechanism of the acid-catalysed hydrolysis of the carbonatotetraimidazolecobalt(III) ion

The kinetics of the acid-catalysed hydrolysis of the [(imidazole)(4)Co(CO3)](+) ion was found to follow the rate law -dln[complex]/dt = k(1)K[H+]/(1 + K[H+]) in the 25-45 degrees C range, [H+] 0.05-1.0 M range and I = 1.0 M. The reaction sequence consists of a rapid protonation equilibrium followed by the one-end dissociation of the coordinated carbonate ligand (rate-determining step) and subsequent fast release of the monodentate carbonate ligand. The rate parameter values, k(1) and K, at 25 degrees C are 6.48 x 10(-3) s(-1) and 0.31 M(-1), respectively, and activation parameters for k(1) are Delta H-1(not equal) = 86.1 +/- 1.2 kJ mol(-1) and Delta S-not equal = 2.1 +/- 6.3 J mol(-1) K-1. The hydrolysis rate increases with increase in ionic strength. The different ways of dealing with the data fit are presented and discussed. The kinetic results are compared with those for the similar cobalt(III) complexes.