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Title: Kinetics and mechanism of acid and base hydrolysis of cis-(bioxalato) (imidazole)bis(ethylenediamine)cobalt (III) ion: A study of the role of the coordinated imidazole and its anion
Authors: Dash, Anadi C
Nanda, Rabindra K
Acharya, Achyuta N
Issue Date: Nov-1992
Publisher: NISCAIR-CSIR, India
Abstract: The aquation and base hydrolysis of cis-[(en)2(imH)CoC2O4H]2 + (imH = imidazole) have been investigated in 1.0 mol dm-3 (CIO), ionic strength. The aquation of the complex at [H+] = 0.50-1.0 mol dm-3 (60°C) proceeds via spontaneous and H+ catalysed paths, kobs = k + KH[H+], with k = (1.2± 0.2) x 10-6 s-1 and kH= (3.2± 0.4)10-6 dm3 mol-1 s-1. In the range [OH-]T = 0.010-1.0 mol dm-3 and 15-35°C, the complex exists in doubly deprotonated form, cis-[(en)2Co(im)C2O4] and the pseudo-first order rate constant fits the relationship, kobs, =  k0 + k1[OH-] + k2[OH-]2. The rate constants (k0, k1, and k and the associated activation parameters (H and S) arc reported. Comparison of k0 and k show that imidazolate anion (im-) has stronger σ-bonded labilisation of Co - O bond relative to imidazole. Base hydrolysis in 50%  medium results in rate acceleration relative to aqueous medium, and kobs = k1[OH-l]T is obeyed at [OH-] T = 0.050-0.70 mol dm-3 (30°C).
Page(s): 832-837
ISSN: 0975-0975(Online); 0376-4710(Print)
Appears in Collections:IJC-A Vol.31A(11) [November 1992]

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