Kinetics and mechanism of anation of β-cis-(diaquo)-(trien)cobalt(III) by oxalate

Dasha, A. C. ; Nandaa, R. K. ; Raya, Nityananda (1982) Kinetics and mechanism of anation of β-cis-(diaquo)-(trien)cobalt(III) by oxalate Journal of Coordination Chemistry, 11 (4). pp. 213-217. ISSN 0095-8972

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Official URL: http://www.tandfonline.com/doi/abs/10.1080/0095897...

Related URL: http://dx.doi.org/10.1080/00958978208079739

Abstract

The anation of β-cis-[Co(trien)(OH2)2]3+ ion by oxalic acid, bioxalate anion and oxalate dianion has been studied at 30-45°C and I = 1.0 M (KNO3). The common anation rate constant, k 0, of {β-cis-[Co(trien)(OH2)2]3+, H2C2O4} and {β-cis-[Co(trien)(OH2)2]3+, HC2O4 -} ion-pairs is found to be 6.7 × 10-5 sec-1 at 40°C. The observed anation rate constant levels off to a limiting value (7.0 (·0.8) X 10-3, sec-1) at 40°C, pH = 4.00 (·0.05) and [C2O4 2-] ± 0.15 M, which is characteristic of the anation rate constant (k 1) of the oxalate dianion ion-pair. Activation enthalpy and entropy for the k 0 and k 1, paths are 24.5 K.cal mole-1, 0.8 cal. deg-1 mole-1 and 28.9 K.cal mole-1, 24.0 cal. deg-1 mole-1, respectively. The temperature independent ion-pair equilibrium constant for H2C2O4 ion-pair was found to be 6.8 (·1.2) M-1. The anation of {β-cis-[Co(trien)(OH2)2]3+-X} ion pairs (X = H2C2O4, HC2O4- or C2C4is believed to involve an 'Id' mechanism.

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