Nitrosyl-nitrite interconversion in pentacyanoruthenate(II) complexes
The nucleophilic addition of OH- to [Ru(CN)5(NO)]2- leads to the N-bonded pentacyanonitroruthenate(II) ion (λmax = 320 nm, ε = 3850 dm3 mol-1 cm-1). The stoichiometry is 2:1 ([OH-]:[Ru]) and the equilibrium formation constant is 4.4 × 106 dm6 mol-2 (25 °C, I = 1 mol dm-3). A kinetic study of the for...
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| Autores principales: | , , |
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| Formato: | JOUR |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_14727773_v_n8_p1959_Chevalier |
| Aporte de: |
| Sumario: | The nucleophilic addition of OH- to [Ru(CN)5(NO)]2- leads to the N-bonded pentacyanonitroruthenate(II) ion (λmax = 320 nm, ε = 3850 dm3 mol-1 cm-1). The stoichiometry is 2:1 ([OH-]:[Ru]) and the equilibrium formation constant is 4.4 × 106 dm6 mol-2 (25 °C, I = 1 mol dm-3). A kinetic study of the forward reaction showed that it is first order in the concentration of each reactant, with k = 0.95 dm3 mol-1 s-1 (25 °C, I = 1 mol dm-3), ΔH‡ = 57.3 ± 3.3 kJ mol-1 and ΔS‡ = -54.0 ± 4.5 J K-1 mol-1. The mechanism involves two consecutive attacks by OH-, the first being rate determining. The reaction product decays by an aquation process, leading to [Ru(CN)5(H2O)]3- and free NO2 -. The rate constant for the dissociation reaction of [Ru(CN)5(NO2)]4- is k-N = 2.00 × 10-4 s-1 (25 °C, I = 1 mol dm-3). In the formation reaction, both nitrite (O-bound) and nitro (N-bound) linkage isomers are formed, with kO and kN being 0.23 and 0.15 dm3 mol-1 s-1 respectively (25 °C, I = 1 mol dm-3). The O-bound isomer isomerizes slowly to the thermodynamically more stable N-bound isomer. The kinetic and thermodynamic parameters have been analysed by comparison with the chemistry of the complexes [Fe(CN)5(NO)]2- and [Fe(CN)5(NO2)]4-. |
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