Summary
The kinetics of aqua ligand substitution fromcis-[Coen2(H2O)2]3+ by quinolinic acid have been studied spectrophotometrically in the 40 to 55°C range. At pH 4.05 the quinolinic acid H2Quin behaves as uninegative and bidentate (O, O) donor. The replacement of water was found to involve two consecutive step processes. The first is the replacement of one water fromcis-[Coen2(H2O)2]3+ by unidentate HQuin−, involving prior establishment of an ion-pairing associative equilibrium, followed by dissociative interchange. The second step is the slower chelation step, where another water molecule is replaced. The rate constants for both the steps and the ion-pair equilibrium constant for the first step have been evaluated. The activation parameters for the two steps are: ΔH ‡1 =117.2 kJ mol−1, ΔH ‡2 =100.5 kJ mol−1 and ΔS ‡1 =69.4 JK−1 mol−1, ΔS ‡2 =12.1 JK−1 mol−1. A probable mechanism for the substitution process is suggested.
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Banerjee, K., Niyogy, B. & De Sankar, G. Kinetics of substitution of aqua ligands fromcis-diaqua-bis(ethylene-diamine) cobalt(III) ion by quinolinic acid in water-ethanol mixtures. Transition Met Chem 12, 241–245 (1987). https://doi.org/10.1007/BF01023539
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DOI: https://doi.org/10.1007/BF01023539