Kinetics and mechanism of aquation of cis (ammine)bis(ethylenediamine) (substituted salicylato)cobalt(III) complexes

Dash, A. C. ; Mohanty, Brundaban (1977) Kinetics and mechanism of aquation of cis (ammine)bis(ethylenediamine) (substituted salicylato)cobalt(III) complexes Journal of Inorganic and Nuclear Chemistry, 39 (7). pp. 1179-1184. ISSN 0022-1902

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/002219...

Related URL: http://dx.doi.org/10.1016/0022-1902(77)80341-2

Abstract

The kinetics of aquation of cis (ammine)bis(ethylenediamine) (substituted salicylato)cobalt(III) complexes, [(en)2(NH3)CoCO2C6H3(X)OH]2+ (X = H, 5-SO3-, 5-Br, 5-NO2, 3-NO2), has been investigated in aqueous perchlorate medium of I = 2.0 M and at 55-70°. The observed rate constant for aquation over the acidity range [H+] = 0.1-2.0 M is given by kobs = k0 + k1[H+] where k0 and k1 are the rate constants associated with the spontaneous and acid catalysed paths respectively. Attempt to determine the protonation constant of the complexes was unsuccessful. The rate and activation parameters for the k0 and k1 paths have been determined. k0 increases with increasing electron withdrawing effect of the substituents, but this decreases k1. The substituent effect on both the paths is, however, small. The activation parameters for both paths obey the isokinetic relationship. Both SO4- and HSO4- catalyse the aquation process. The stability and reactivity of the sulphate ion-pairs have been assessed. The log k0 vs pKeq plot, where Keq is the formation constant of the salicylato complexes, is linear with unit slope. The results support rate limiting by Co---O bond breaking in the k0 and k1 paths.

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