Structural and mechanistic studies of co-ordination compounds. Part II. Preparation, aquation, and base hydrolysis of trans-chloronitro- and trans-bromonitro-tetra-amminecobalt(III) cations

Abstract

The preparation and characterization of trans-[Co(NH3)4NO2Cl]+ and trans-[Co(NH3)4NO2Br]+ cations are described. The assignment of geometric configuration is based on 1H n.m.r. spectroscopy. The kinetics of the aquation and base hydrolysis of these two complex cations have been studied over a range of temperature. The first-order aquation rate constants are greater than those of the corresponding bis(ethylenediamine) and 1,4,8,11-tetra-azacyclotetradecane complexes, whereas the second-order base hydrolysis rate constants are less. These results are consistent with the kinetic nephelauxetic effect of these amine ligands on the central cobalt(III) ion. Unimolecular reaction mechanisms are assigned to these reactions.