title: Iron nitrosyls of a pentadentate ligand containing a single carboxamide group: syntheses, structures, electronic properties, and photolability of NO.
abstract: Three iron complexes of a pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy(3)H, H is the dissociable amide proton) have been synthesized. All three species, namely, two nitrosyls [(PaPy(3))Fe(NO)](ClO(4))(2) (2) and [(PaPy(3))Fe(NO)](ClO(4)) (3) and one nitro complex [(PaPy(3))Fe(NO(2))](ClO(4)) (4), have been structurally characterized. These complexes provide the opportunity to compare the structural and spectral properties of a set of isostructural [Fe-NO](6,7) complexes (2 and 3, respectively) and an analogous genuine Fe(III) complex with an "innocent" sixth ligand ([(PaPy(3))Fe(NO(2))](ClO(4)), 4). The most striking difference in the structural features of 2 and 3 is the Fe-N-O angle (Fe-N-O = 173.1(2) degrees in the case of 2 and 141.29(15) degrees in the case of 3). The clean (1)H NMR spectrum of 2 in CD(3)CN 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 approximately 2.00, and variable temperature magnetic susceptibility measurements indicate the S = (1)/(2) spin state of the [Fe-NO](7) complex 3. Analysis of the spectroscopic data suggests Fe(II)-NO(+) and Fe(II)-NO(*) formulations for 2 and 3, respectively. The bound NO in 3 does not show any photolability. However, in MeCN solution, it reacts rapidly with dioxygen to afford the nitro complex 4, which has also been synthesized independently from [(PaPy(3))Fe(MeCN)](2+) and NO(2)(-). Nucleophilic attack of hydroxide ion to the N atom of the NO ligand in 2 in MeCN in the dark gives rise to 4 in high yield.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, USA.
authors.forename: Apurba K
authors.initials: AK
authors.lastname: Patra
authors.forename: John M
authors.initials: JM
authors.lastname: Rowland
authors.forename: Dana S
authors.initials: DS
authors.lastname: Marlin
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Marilyn M
authors.initials: MM
authors.lastname: Olmstead
authors.forename: Pradip K
authors.initials: PK
authors.lastname: Mascharak
mesh_terms: D000577:Amides / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D004583:Electrons; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009569:Nitric Oxide / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry*
chemical_list: D000577:Amides; D002264:Carboxylic Acids; D008024:Ligands; D009589:Nitrogen Oxides; D009569:Nitric Oxide; C073661:dinitrosyl iron complex; D007501:Iron