Kinetics and mechanism of dissociation of di-(2-pyridyl)amine complexes copper (II), nickel (II) and cobalt (II) in aqueous acid media

Abstract

Kinetics of dissociation of ML<img src='http://www.niscair.res.in/jinfo/twoplustwo.gif' border=0>+ (M = eu(II), Ni(II)) and CoL²⁺ [L=di-(2-pyridyl)amine] complexes in acid media forming aqua-metal ions and the protonated ligand as the ultimate products have been studied by stopped-flow spectrophotometry. Dissociation of the bis-complexes occurs in two consecutive steps through formation of the mono complexes in the first step, which is faster than the second. For each of the steps of the different complexes the observed rate constant <i>k</i>_x shows acid dependence. Arguments have been put forth in favour of chelate ring-opening as the rate-determining step. These complexes are much more labile to dissociation than the corresponding complexes of 2,2' -bipyridyl.