Current Research

The “elusive” complexes of heme-modeling iron-porphyrins with nitrogen dioxide (NO₂) have been obtained and spectrally characterized (Scheme 1). It is 5-coordinate O-bound nitrito complex Fe(Por)(ONO). These species are fairly stable at ambient conditions and slowly decomposes within few days resulting mostly iron nitrosyls. This observation throws some light on the mechanism of vasodilatation activity of nitrite ion in mammalian biology.

Scheme 1.

Some chemical properties of this new complex are studied:

Interaction with nitric oxide (NO) at low temperature conditions leads to the formation of nitrito-nitrosyl complex Fe(Por)(NO)(ONO) that isomerizes to more stable known nitro-nitrosyl species Fe(Por)(NO)(NO₂) upon warming (Scheme 2).

Scheme 2.

Isomerization occurs through the mechanism of NO₂ flipping from O- to N-bound form rather than the elimination of O-coordinated NO₂ ligand followed by formation of new Fe-N(NO₂) bond.

Interaction with electron-donor ligands (B) leads to the formation of 6-coordinate nitro complexes Fe(Por)(NO₂)(B).

Low-temperature NO disproportionation reaction performed by solid state Mn-Porphyrins has been discovered and studied in detail. The mechanism of disproportionation reaction is offered according to the scheme 3. Incidentally new 6-coordinate nitrito-nitrosyl and nitro-nitrosyl complexes {Mn(Por)(ONO)(NO) and Mn(Por)(NO₂)(NO)} were identified at low-temperature conditions.

Scheme 3.

Previously unknown 6-coordinate nitrosyl complexes of Co-porphyrins with trans N-donor ligands have been obtained at low-temperature conditions and spectrally characterized. (Scheme 4).

Scheme 4.

The same behavior reveals Co-complexes of mono-4(3)-pyridyl-triphenyl porphyrins that in sublimed layers form coordination oligomers. Low-temperature interaction of NO gas with these self-organized supramolecular assemblies leads to the formation of 5- and 6-coordinate nitrosyl complexes represented at the Fig.

These microporous systems containing unsaturated metal atoms in their frameworks reveal promising properties to serve as a solid state NO-storage agents and selective adsorbents.