KINETICS AND MECHANISM OF AQUATION AND BASE HYDROLYSIS OF NITRATOPENTAAMMINECOBALT(III) ION AND RELATED COMPLEXES

The kinetics of aquation of Co(NH3)5NO3 2+ in acidic perchlorate media of ionic strength I = 0.12 M are first order in complex concentration and are represented over the temperature range 0-59° by ΔH1%25 = 24.34 kcal mol-1, ΔS1%25 = 1.9 cal deg-1 mol-1, and ΔCP% = -20 cal deg-1 mol-1. Base hydrolysis of Co(NH3)5NO32+ is strictly first order in [OH-] up to 0.2 M at least, and first order in [complex]; the kinetic data are represented by ΔH2% - 28.8 kcal mol-1 and ΔS2% = 43 cal deg-1 mol-1, from 2 to 35° at I = 0.12 M in perchlorate media. In either reaction, the Co-O bond is the one which is broken in the transition state. Linear relationships of unit slope exist between the free energy of activation and the standard free energy change of reaction in both aquation and base hydrolysis of complexes of the type Co(NH3)5X2+. A dissociative mode of activation common to both types of reaction is indicated. © 1969, American Chemical Society. All rights reserved.