- Kinetics, mechanism, and spectroscopy of the reversible binding of nitric oxide to aquated iron(II). An undergraduate text book reaction revisited
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A detailed kinetic and mechanistic analysis of the classical brown-ring reaction of [Fe(H2O)6]2+ with NO was performed using stopped-flow and laser flash photolysis techniques at ambient and high pressure. The kinetic parameters for the on and off reactions at 25 °C were found to be kon = 1.42 × 106 M-1 s-1, ΔH?on = 37.1 ± 0.5 kJ mol-1, ΔS?on = -3 ± 2 J K-1 mol-1, ΔV?on = +6.1 ± 0.4 cm3 mol-1, and koff = 3240 ± 750 s-1, ΔH?off = 48.4 ± 1.4 kJ mol-1, ΔS?off = -15 ± 5 J K-1 mol-1, ΔV?off = +1.3 ± 0.2 cm3 mol-1. These parameters suggest that both reactions follow an interchange dissociative (ld) ligand substitution mechanism, which correlates well with the suggested mechanism for the water exchange reaction on [Fe(H2O)6]2+. In addition, Moessbauer spectroscopy and EPR measurements were performed on the reaction product [Fe(H2O)5(NO)]2+. The Moessbauer and EPR parameters closely resemble those of the {FeNO}7 units in any of the other well-characterized nitrosyl complexes. It is concluded that its electronic structure is best described by the presence of high-spin FeIII antiferromagnetically coupled to NO- (S = 1) yielding the observed spin quartet ground state (S = 3/2), i.e., [FeIII(H2O)5(NO-)]2+, and not [FeI(H2O)5(NO+)]2+ as usually quoted in undergraduate text books.
- Wanat, Alicja,Schneppensieper, Thorsten,Stochel, Grazyna,Van Eldik, Rudi,Bill, Eckhard,Wieghardt, Karl
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- Kinetic Study of Ferrous Nitrosyl Complexes
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The formation and dissociation rate constants and equilibrium constants for the reversible binding of NO to FeII(H2O)5, FeII(cit), FeII(acac)2, and FeII(EDTA) in aqueous solution are reported (cit = citrate, aca
- Littlejohn, D.,Chang, S. G.
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p. 537 - 540
(2007/10/02)
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