title: Dinitrosyl iron complexes (DNICs) bearing O-bound nitrito ligand: reversible transformation between the six-coordinate {Fe(NO)2}9 [(1-MeIm)2(eta(2)-ONO)Fe(NO)2] (g = 2.013) and four-coordinate {Fe(NO)2}9 [(1-MeIm)(ONO)Fe(NO)2] (g = 2.03).
abstract: In contrast to the four-coordinate tetrahedral {Fe(NO)2}9 DNICs with an EPR g value of 2.03, the newly synthesized nonclassical six-coordinate {Fe(NO)2}9 DNIC [(1-MeIm)2(eta(2)-ONO)Fe(NO)2] (1-MeIm = 1-methylimidazole) (1) displays an EPR signal g = 2.013. The temperature-dependent reversible transformation occurs between the six-coordinate chelating nitrito {Fe(NO)2}9 DNIC 1 and the four-coordinate monodentate nitrito {Fe(NO)2}9 DNIC [(1-MeIm)(ONO)Fe(NO)2] (2-MeIm). The chelating nitrito of DNIC 1, triggered by PPh3, undergoes O-atom transfer to yield O=PPh3, accompanied by reductive elimination of NO and the generation of {Fe(NO)2}10 DNIC [(1-MeIm)(PPh3)Fe(NO)2] (3), in contrast to the inertness of the nitrite-containing {Fe(NO)2}9 DNIC [(HIm)(ONO)Fe(NO)2] (HIm = imidazole) (2-HIm) toward PPh3. The findings, EPR signals of g = 2.013 for complex 1 and g = 2.03 for complexes 2-MeIm/2-HIm, imply that characterization of DNICs may be possible via their distinctive EPR signal g = 2.03 for the tetrahedral DNICs and EPR signal g = 2.01 for the six-coordinate DNICs. This study also implicates that the six-coordinate nitrite-containing {Fe(NO)2}9 DNICs may act as a transient intermediate (or an active center) to trigger the transformation of nitrite into nitric oxide.
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan.
authors.forename: Fu-Te
authors.initials: FT
authors.lastname: Tsai
authors.forename: Ting-Shen
authors.initials: TS
authors.lastname: Kuo
authors.forename: Wen-Feng
authors.initials: WF
authors.lastname: Liaw
mesh_terms: D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009589:Nitrogen Oxides / Q000737:chemistry*
chemical_list: D008024:Ligands; D009589:Nitrogen Oxides; C073661:dinitrosyl iron complex; D007501:Iron