Portal de Periódicos da CAPES

Interaction of Nitrogen Bases with Iron−Porphyrin Nitrito Complexes Fe(Por)(ONO) in Sublimed Solids

2007; American Chemical Society; Volume: 46; Issue: 17 Linguagem: Inglês

10.1021/ic700846x

1520-510X

Tigran S. Kurtikyan, Astghik A. Hovhannisyan, Gurgen M. Gulyan, Peter C. Ford,

Electrochemical Analysis and Applications

The reactions of the nitrogen Lewis bases (B) 1-methylimidazole (1-MeIm), pyridine (Py), and NH3 as gases with sublimed layers containing the 5-coordinate nitrito iron(III)−porphyrinato complexes Fe(Por)(η1-ONO) (1) are described (Por = meso-tetraphenyl-porphyrinato or meso-tetra-p-tolyl-porphyrinato dianions). In situ FTIR and optical spectra are used to characterize the formation of the 6-coordinate nitro complexes formed by the reaction of 1 with B = 1-MeIm, Py, or NH3. These represent the first examples of 6-coordinate amino−nitro complexes with sterically unprotected iron−porphyrins. The interaction of ammonia with Fe(Por)(ONO) at 140 K initially led to the nitrito species Fe(Por)(NH3)(η1-ONO), and this species isomerized to the nitro complexes Fe(Por)(NH3)(η1-NO2) upon warming to 180 K. When the latter were warmed to room temperature under intense pumping, the initial nitrito complexes Fe(Por)(η1-ONO) were restored. Assignments of vibrational frequencies for the coordinated nitro group in 6-coordinate iron−porphyrin complexes are given and confirmed using 15N-labeled nitrogen dioxide to identify characteristic infrared bands. For M(Por)(B)(NO2) complexes (M = Fe or Co), an inverse correlation between the net charge transfer from the axial ligand B to the nitro group and the value of Δν = νa(NO2) − νs(NO2) is proposed. These observations are discussed in the context of growing interest in potential physiological roles of nitrite ion reactions with ferro− and ferri−heme proteins.