| Abstract
| - Three iron complexes of a pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide(PaPy3H, H is the dissociable amide proton) have been synthesized. All three species, namely, two nitrosyls [(PaPy3)Fe(NO)](ClO4)2 (2) and [(PaPy3)Fe(NO)](ClO4) (3) and one nitro complex [(PaPy3)Fe(NO2)](ClO4) (4), have beenstructurally characterized. These complexes provide the opportunity to compare the structural and spectral propertiesof a set of isostructural {Fe−NO}6,7 complexes (2 and 3, respectively) and an analogous genuine Fe(III) complexwith an “innocent” sixth ligand ([(PaPy3)Fe(NO2)](ClO4), 4). The most striking difference in the structural featuresof 2 and 3 is the Fe−N−O angle (Fe−N−O = 173.1(2)° in the case of 2 and 141.29(15)° in the case of 3). Theclean 1H NMR spectrum of 2 in CD3CN reveals its S = 0 ground state and confirms its {Fe−NO}6 configuration.The binding of NO at the non-heme iron center in 2 is completely reversible and the bound NO is photolabile.Mössbauer data, electron paramagnetic resonance signal at g ≈ 2.00, and variable temperature magnetic susceptibilitymeasurements indicate the S = 1/2 spin state of the {Fe−NO}7 complex 3. Analysis of the spectroscopic datasuggests Fe(II)−NO+ and Fe(II)−NO• formulations for 2 and 3, respectively. The bound NO in 3 does not show anyphotolability. However, in MeCN solution, it reacts rapidly with dioxygen to afford the nitro complex 4, which hasalso been synthesized independently from [(PaPy3)Fe(MeCN)]2+ and NO2-. Nucleophilic attack of hydroxide ion tothe N atom of the NO ligand in 2 in MeCN in the dark gives rise to 4 in high yield.
- Two iron nitrosyls derived from the pentadentate ligand Papy3H, namely, [(PaPy3)Fe(NO)](ClO4) (2) and [(PaPy3)Fe(NO)](ClO4)2 (3), constitute a set of isostructural {Fe−NO}6,7 complexes. The formally Fe(III) species 2 exhibits photolability of NO under low-intensity illumination, and the binding of NO is reversible. The formally Fe(II) species 3 does not show any such reactivity.
|
