Six-Coordinate Nitrito and Nitrato Complexes of Manganese Porphyrin

Reaction of small increments of NO2 gas with sublimed amorphous layers of Mn(II)(TPP) (TPP = meso-tetra-phenylporphyrinato dianion) in a vacuum cryostat leads to formation of the 5-coordinate monodentate nitrato complex Mn(III)(TPP)(η(1)-ONO2) (II). This transformation proceeds through the two distinct steps with initial formation of the five coordinate O-nitrito complex Mn(III)(TPP)(η(1)-ONO) (I) as demonstrated by the electronic absorption spectra and by FTIR spectra using differently labeled nitrogen dioxide. A plausible mechanism for the second stage of reaction is offered based on the spectral changes observed upon subsequent interaction of (15)NO2 and NO2 with the layered Mn(TPP). Low-temperature interaction of I and II with the vapors of various ligands L (L = O-, S-, and N-donors) leads to formation of the 6-coordinate O-nitrito Mn(III)(TPP)(L)(η(1)-ONO) and monodentate nitrato Mn(III)(TPP)(L)(η(1)-ONO2) complexes, respectively. Formation of the 6-coordinate O-nitrito complex is accompanied by the shifts of the ν(N═O) band to lower frequency and of the ν(N-O) band to higher frequency. The frequency difference between these bands Δν = ν(N═O) - ν(N-O) is a function of L and is smaller for the stronger bases. Reaction of excess NH3 with I leads to formation of Mn(TPP)(NH3)(η(1)-ONO) and of the cation [Mn(TPP)(NH3)2](+) plus ionic nitrite. The nitrito complexes are relatively unstable, but several of the nitrato species can be observed in the solid state at room temperature. For example, the tetrahydrofuran complex Mn(TPP)(THF)(η(1)-ONO2) is stable in the presence of THF vapors (∼5 mm), but it loses this ligand upon high vacuum pumping at RT. When L = dimethylsulfide (DMS), the nitrato complex is stable only to ∼-30 °C. Reactions of II with the N-donor ligands NH3, pyridine, or 1-methylimidazole are more complex. With these ligands, the nitrato complexes Mn(III)(TPP)(L)(η(1)-ONO2) and the cationic complexes [Mn(TPP)(L)2](+) coexist in the layer at room temperature, the latter formed as a result of NO3(-) displacement when L is in excess

Six-coordinate nitrito and nitrato complexes of manganese porphyrin.

Reaction of small increments of NO2 gas with sublimed amorphous layers of Mn(II)(TPP) (TPP = meso-tetra-phenylporphyrinato dianion) in a vacuum cryostat leads to formation of the 5-coordinate monodentate nitrato complex Mn(III)(TPP)(η(1)-ONO2) (II). This transformation proceeds through the two distinct steps with initial formation of the five coordinate O-nitrito complex Mn(III)(TPP)(η(1)-ONO) (I) as demonstrated by the electronic absorption spectra and by FTIR spectra using differently labeled nitrogen dioxide. A plausible mechanism for the second stage of reaction is offered based on the spectral changes observed upon subsequent interaction of (15)NO2 and NO2 with the layered Mn(TPP). Low-temperature interaction of I and II with the vapors of various ligands L (L = O-, S-, and N-donors) leads to formation of the 6-coordinate O-nitrito Mn(III)(TPP)(L)(η(1)-ONO) and monodentate nitrato Mn(III)(TPP)(L)(η(1)-ONO2) complexes, respectively. Formation of the 6-coordinate O-nitrito complex is accompanied by the shifts of the ν(N═O) band to lower frequency and of the ν(N-O) band to higher frequency. The frequency difference between these bands Δν = ν(N═O) - ν(N-O) is a function of L and is smaller for the stronger bases. Reaction of excess NH3 with I leads to formation of Mn(TPP)(NH3)(η(1)-ONO) and of the cation [Mn(TPP)(NH3)2](+) plus ionic nitrite. The nitrito complexes are relatively unstable, but several of the nitrato species can be observed in the solid state at room temperature. For example, the tetrahydrofuran complex Mn(TPP)(THF)(η(1)-ONO2) is stable in the presence of THF vapors (∼5 mm), but it loses this ligand upon high vacuum pumping at RT. When L = dimethylsulfide (DMS), the nitrato complex is stable only to ∼-30 °C. Reactions of II with the N-donor ligands NH3, pyridine, or 1-methylimidazole are more complex. With these ligands, the nitrato complexes Mn(III)(TPP)(L)(η(1)-ONO2) and the cationic complexes [Mn(TPP)(L)2](+) coexist in the layer at room temperature, the latter formed as a result of NO3(-) displacement when L is in excess

Spectral study of the reactions of dimethyl sulfoxide with the nitrite complexes of Co-porphyrins

It is revealed by FTIR and electron absorption spectroscopy that the reactions of dimethyl sulfoxide with the nitro complexes of Co-porphyrins both in the solid phase and an inert solvent afford six-coordinate complexes with the general formula (DMSO)Со(Por)(NO2) (Por is meso-tetraphenyl- and meso-tetra-p-tolylporphyrinato dianions). These compounds are stable in the solid state, whereas they partially decompose in an inert solvent to form five- and six-coordinate complexes. The ambident nitrite and dimethyl sulfoxide ligands are coordinated to the metal atom through the N and O atoms, respectively, which was confirmed by the application of isotope-containing compounds 15NO2 and DMSO-d6. © 2018, Springer Science+Business Media, LLC, part of Springer Nature

IR Study of the Interaction of Dioxygen with [meso-Triphenyl(4-pyridyl)porphyrinato]cobalt(II)

The interaction of O2 (18O2) with [meso-triphenyl(4-pyridyl)porphyrinato]cobalt(II) [Co(MPyTPP)] has been investigated by means of IR spectroscopy under matrix-isolation conditions and by the action of dioxygen on thin sublimed layers. These studies have led to the characterisation of two dioxygen adducts: (1) a very unstable dioxygen adduct similar to that observed earlier for the closely related [meso-tetraphenylporphyrinato]cobalt(II) Co(TPP), and (2) a new type of coordinated O2 (18O2) complex which is formed after warming Co(MPyTPP) either in pure oxygen matrices, or as sublimed layers in the presence of oxygen. The ?(O2) vibration in this second species is more than 100 cm-1 lower than in the first, and the dioxygen adduct thus formed is thermally stable at 200 K. This adduct is identified as a six-coordinate dioxygen complex, with one coordination site occupied by the pyridyl group of an adjacent Co(MPyTPP) molecule. In the sublimed layers, the capacity for self-assembly of Co(MPyTPP) oligomers leads to the formation of microporous solids containing coordinatively unsaturated metal ions which have the ability to bind oxygen reversibly upon storage at ambient conditions