Structural and mechanistic studies of co-ordination compounds. Part IV. The preparation, aquation, and base hydrolysis of trans-chloronitro- and trans-bromonitro-(1,4,8,11-tetra-azacyclotetradecane)cobalt-(III) cations

Abstract

The preparation and characterization of trans-[Co(cyclam)NO₂Br]⁺ cation is described. The kinetics of the aquation and base hydrolysis of this complex cation and those of the base hydrolysis of trans-[Co(cyclam)NO₂Cl]⁺ have been studied over a range of temperature. The first-order aquation rate constants are slower than those of the corresponding bis(ethylenediamine) and tetra-ammine analogues, whereas the second-order base hydrolysis rate constants are faster. These results support the earlier prediction made on the basis of the kinetic nephelauxetic effect of these amine ligands on the central cobalt(III) ion. Unimolecular mechanisms are assigned to these reactions.