Spectroscopic Evidence of Hyponitrite Radical Intermediate in NO Disproportionation at a MOF-Supported Mononuclear Copper Site

Dianionic hyponitrite (N₂O₂²⁻) is often proposed, based on model complexes, as the key intermediate in reductive coupling of nitric oxide to nitrous oxide at the bimetallic active sites of heme-copper oxidases and nitric oxide reductases. In this work, we examine the gas-solid reaction of nitric oxide with the metal–organic framework Cu^I-ZrTpmC* with a suite of in situ spectroscopies and density functional theory simulations, and identify an unusual chelating N₂O₂^.− intermediate. These results highlight the advantage provided by site-isolation in metal–organic frameworks (MOFs) for studying important reaction intermediates, and provide a mechanistic scenario compatible with the proposed one-electron couple in these enzymes.