Octahedral cobalt(III) complexes of the chloropentammine type. Part II. The solvolytic aquation and hydrolysis by base of cis-chloromethylamine- and cis-chloroethylamine-bis(ethylenediamine)cobalt(III) cations

Abstract

Nitrates of one isomeric form of the chloromethylamine- and chloroethylamine-bis(ethylenediamine)cobalt(III) cations have been prepared and characterised. These complexes have been assigned a cis-configuration on the basis of infrared spectral observations. The first-order rate constants for their solvolytic aquation have been determined at different temperatures and the Arrhenius parameters calculated. The lower rates than of the corresponding chloro-ammine complex support an S_N2 mechanism, by which one water molecule in the solvation shell is exchanged synchronously with the co-ordinated chlorine ligand in the complex. The second-order rate constants for the hydrolysis of these cations by base have also been determined at 0° and ionic strength 0·1M. By comparison with the corresponding chloro-ammine system, these results are discussed in terms of the S_N2/P mechanism postulated in Part I. The analogy between solvolytic aquation and base hydrolysis is also discussed.