Metallonitrosyl fragment as electron acceptor: Intramolecular charge transfer, long range electronic coupling, and electrophilic reactivity in the trans-[NCRu(py)4(CN)Ru(py)4NO]3+ Ion
The new complex trans-[NCRu(py)4(CN)Ru(py)4NO] (PF6)3 (I) was synthesized. In acetonitrile solution, I shows an intense visible band (555 nm, ε = 5800 M-1 cm-1) and other absorptions below 350 nm, associated with dπ → π*py and πpy → π*py transitions. The visible band is presently assigned as a donor...
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| Autores principales: | , , , |
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| Publicado: |
2002
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00201669_v41_n7_p1930_Roncaroli http://hdl.handle.net/20.500.12110/paper_00201669_v41_n7_p1930_Roncaroli |
| Aporte de: |
| Sumario: | The new complex trans-[NCRu(py)4(CN)Ru(py)4NO] (PF6)3 (I) was synthesized. In acetonitrile solution, I shows an intense visible band (555 nm, ε = 5800 M-1 cm-1) and other absorptions below 350 nm, associated with dπ → π*py and πpy → π*py transitions. The visible band is presently assigned as a donor-acceptor charge transfer (DACT) transition from the remote Ru(II) to the delocalized {RuII-NO+} moiety. Photoinduced release of NO is observed upon irradiation at the DACT band. Application of the Hush model reveals strong electronic coupling, with HDA = ∼2000 cm-1. The difference between the optical absorption energy and redox potentials for the donor and acceptor sites (RuIII,II, 1.40 V, and NO+/NO, 0.50 V, vs Ag/AgCl, 3 M KCl, respectively) (hν - ΔEred) is 1.33 eV, a large value which probably relates to the significant changes in distances and angles for the Ru-N-O moiety upon reduction. UV-vis absorptions, IR frequencies, and redox potentials are solvent-dependent. Controlled potential reduction (of NO+) and oxidation (of Ru(II) associated with the dicyano-chromophore) of I afford stable species, [NCRuII(py)4(CN)Ru(py)4NO]2+ (Ired) and [NCRuIII(py)4(CN)Ru(py)4NO]4+ (Iox), respectively, which are characterized by UV-vis and IR spectroscopies. Ired shows an EPR spectrum characteristic of {Ru(II)-NO•} complexes. Compound I is electrophilically reactive in aqueous solution above pH 5: values of the equilibrium constant for the reaction [NCRu(py)4(CN)Ru(py)4NO]3++ 2 OH- ⇄ [NCRu(py)4(CN)Ru(py)4NO2]+ + H2O, K = 3.2 ± 1.4 × 1015 M-2, and of the rate constant for the nucleophilic addition of OH-, k = 9.2 ± 0.2 × 103 M-1 s-1(25 °C, I = 1 M), are obtained, with ΔΗ‡ = 90.7 ± 3.8 kJ mol-1 and ΔS‡ = 135 ± 13 J K-1 mol-1. The oxidized complex, Iox, shows an enhanced electrophilic reactivity toward OH-. This addition reaction is followed by irreversible processes, which most probably lead to disproportionation of bound nitrite and other products. |
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