OXIDATION SEQUENCE OF SUBLIMED MESO-TETRAPHENYLPORPHYRINATOCOBALT(II)FILMS IN AN ATMOSPHERE OF NITROGEN-DIOXIDE

Sublimed mms of meso-tetraphenylporphyrinatocobalt(II) (CoTPP) undergo a series of chemical transformations in an atmosphere of NO2. In the first stage, at low NO2 pressures, the axial five-coordinate (CoTPP)-T -III . NO2 complex is formed. An increase in the NO2 pressure and/or e xposure results in subsequent oxidation with the formation of a pi-rad ical cation CoTPP.+. In the latter, according to the IR spectral data, nitrogen dioxide is axially coordinated by the cobalt ion. Further in crease in the NO2 pressure leads to both the formation of a dication a nd nitration of the porphyrin ring most likely at the meso- and beta-p yrrolic positions. Irreversible chemical transformations in the sublim ed CoTPP films prevent their use as NO2 sensors.