The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [Cr-III(14-TMC)(O-2)(Cl)](+), with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [Cr-IV(14-TMC)(O)(Cl)](+), via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from electron paramagnetic resonance spectroscopy, computational chemistry and the observation of phenol nitration chemistry. The Cr(IV)-oxo complex does not react with nitrogen dioxide (NO2), but reacts with NO to afford a Cr(III)-nitrito complex, [Cr-III(14-TMC)(NO2)(Cl)](+). The Cr(IV)-oxo and Cr(III)-nitrito complexes were also characterized spectroscopically and/or structurally.