The aquation of cis-Chlorodi(methyl sulphoxide)bisethylenediaminecobalt(III), cis-Chlorodimethylformamidebisethylenediaminecobalt(III), and cis-Chlorodimethylacetamidebisethylenediaminecobalt(III) ions

Abstract

The aquation of each of three octahedral chloro(solvent)bisethylene- diaminecobalt(III) ions, involving the solvent ligands dimethyl sulphoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMA), has been examined in solutions of different pH. In solutions of pH less than 6, the predominant reaction is replacement of the solvent molecule by water in an S_N1 process, involving a trigonal bipyramidal transition state and resulting in a mixture of the trans- and cis- chloroaquo complexes. The slow loss of chloride ion is an accompanying side reaction. In solutions of pH greater than 6 base hydrolysis becomes important, and in alkaline solutions the rate of solvent loss is too fast to measure by conventional techniques. The rate of liberation of chloride ion is also greatly increased with increasing pH. Values of the activation energy, and entropy of activation, are reported for the solvent replacement reaction at a pH of 1.90.