Nitric Oxide Dioxygenation Reaction by Oxy-Coboglobin Models: In-situ Low-Temperature FTIR Characterization of Coordinated Peroxynitrite

The oxy-cobolglobin models of the general formula (NH3)Co(Por)(O2) (Por = meso-tetra-phenyl and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low temperature interaction of NH3 and dioxygen with microporous layers of Co–porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV–visible spectroscopy during slow warming. Upon warming the layers from 80 to 120 K a set of new IR bands grows with correlating intensities along with the consumption of the ν(O2) band. Isotope labeling experiments with 18O2, 15NO and N18O along with DFT calculations provides a basis for assigning them to the six-coordinate peroxynitrite complexes (NH3)Co(Por)(OONO). Over the course of warming the layers from 140 to 170 K these complexes decompose and there are spectral features suggesting the formation of nitrogen dioxide NO2. Upon keeping the layers at 180–210 K the bands of NO2 gradually decrease in intensi...