Dissociation of aqua[tris(2-dimethylaminoethyl)amine-NN′N″N‴]-cobalt(II) and its nickel(II) and copper(II) analogues in perchloric acid solution

Abstract

A stopped-flow spectrophotometric study of the dissociation of five-co-ordinate [Co(tda)H₂O]²⁺[tda = tris-(2-dimethylaminoethyl)amine] and the nickel(II) and copper (II) analogues in acidic 2·0M-ClO₄^– aqueous solution is reported. A single process has been observed for all three metal complexes and is attributed to the dissociation of the first amine group. Kinetic parameters for the cobalt(II), nickel(II), and copper (II) complexes respectively are: k(293 K)= 0·97 ± 0·01 s^–1, ΔH^‡= 61·9 ± 2·9 kJ mol^–1, ΔS‡=–33·5 ± 9·8 J K^–1 mol^–1; 7·87 ± 0·04 s^–1, 58·9 ± 1·3 kJ mol^–1, –26·4 ± 4·6 J K^–1 mol^–1; and 28·0 ± 0·8 s^–1, 81·1 ± 2·5 kJ mol^–1, 59·9 ± 8·4 J K^–1 mol^–1 Possible sources of the variations in the magnitudes of these parameters are discussed in terms of both dissociative and associative reaction mechanisms.