Summary
Kinetic studies of the anation of the title complex by NO −2 show that it occurs in a stepwise manner leading to thecis-dinitro-complex both steps having a common rate equation:-d[complex]/dt = a[NO −2 ]/{[NO −2 ] + b}. The variation ofpseudo-first-order rate constant (kobs) with [NO −2 ] indicates that the reaction proceeds through ion-pair interchange path. Activation parameters calculated by the Eyring equation are: ΔH ≠1 = (65±7) kJ mol−1 and ΔS ≠1 = (−82±11) JK−1 mol−1 for the formation of [Co(NH3)4(NO2)(H2O)]2+, and ΔH ≠2 = (97±1) kJ mol−1 and ΔS ≠2 = (6±2) JK−1 mol−1 for the formation of [Co(NH3)4(NO2)2]+. Anation of the title complex by N −3 at pH 4.1 also occurs in a stepwise manner ultimately producing thecis-diazido species. At a fixed pH the reaction shows a first-order dependence on [N −3 ] for each step. pH-variation studies at a fixed [N −3 ] show that the hydroxoaqua-form of the complex reactsca. 16 times faster than the diaqua form. Evidence is presented for an ion-pair preequilibrium at high ionic strength (I = 2.0 mol dm−3). Activation parameters obtained from temperature variation studies are: ΔH ≠1 = (121±1) kJ mol−1 and ΔS ≠1 = (104±3) JK−1 mol−1 (for the first step anation), and ΔH ≠2 = (111±2) kJ mol−1 and ΔS ≠2 = (74±9) JK−1 mol−1 (for the second step anation). The reaction ofcis-tetraaminediaquacobalt(III) ion with salicylate (HSal−) has been studied in aqueous acidic medium in the temperature range 39.8–58.2°C. The reaction is biphasic corresponding to the anation of two salicylate ions. The kinetic results for the first phase reaction are compatible with the equation: kobs = kIPQ[HSal−]/(1 + Q[HSal−]) where Q denotes ion-pair formation constant and kIP is the first-order rate constant for the interchange reaction. The activation parameters obtained from the temperature dependence of rate are: ΔH≠ = (138±3) kJ mol−1 and ΔS≠ = (135±4) JK−1 mol−1. The reaction seems to take place by a dissociative interchange mechanism.
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Ghosh, M.C., Bhattacharya, P. & Banerjee, P. Kinetics and mechanism of the reactions ofcis-tetraaminediaqua-cobalt(III) with nitrite, azide and salicylate ions in aqueous acidic media. Transition Met Chem 9, 68–73 (1984). https://doi.org/10.1007/BF00619005
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DOI: https://doi.org/10.1007/BF00619005