摘要
A reversible redox reaction ({Fe(NO) 2 } 9 DNIC [(NO) 2 Fe(N(Mes)(TMS)) 2 ] - (4) ⇄ oxidized-form DNIC [(NO) 2 Fe(N(Mes)(TMS)) 2 ] (5) (Mes = mesityl, TMS = trimethylsilane)), characterized by IR, UV-vis, 1 H/ 15 N NMR, SQUID, XAS, single-crystal X-ray structure, and DFT calculation, was demonstrated. The electronic structure of the oxidized-form DNIC 5 (S total = 0) may be best described as the delocalized aminyl radical [(N(Mes)(TMS)) 2 ] 2 -• stabilized by the electron-deficient {Fe III (NO - ) 2 } 9 motif, that is, substantial spin is delocalized onto the [(N(Mes)(TMS)) 2 ] 2 -• such that the highly covalent dinitrosyl iron core (DNIC) is preserved. In addition to IR, EPR (g ≈ 2.03 for {Fe(NO) 2 } 9 ), single-crystal X-ray structure (Fe-N(O) and N-O bond distances), and Fe K-edge pre-edge energy (7113.1-7113.3 eV for {Fe(NO) 2 } 10 vs 7113.4-7113.9 eV for {Fe(NO) 2 } 9 ), the 15 N NMR spectrum of [Fe( 15 NO) 2 ] was also explored to serve as an efficient tool to characterize and discriminate {Fe(NO) 2 } 9 (δ 23.1-76.1 ppm) and {Fe(NO) 2 } 10 (δ -7.8-25.0 ppm) DNICs. To the best of our knowledge, DNIC 5 is the first structurally characterized tetrahedral DNIC formulated as covalent-delocalized [{Fe III (NO - ) 2 } 9 -[N(Mes)(TMS)] 2 -• ]. This result may explain why all tetrahedral DNICs containing monodentate-coordinate ligands isolated and characterized nowadays are confined in the {Fe(NO) 2 } 9 and {Fe(NO) 2 } 10 DNICs in chemistry and biology. © 2013 American Chemical Society.