ISSN:
1572-901X
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
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.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00619005
