NO disproportionation at a mononuclear site-isolated Fe(2+) center in Fe(2+)-MOF-5

The weak-field ligand environments at the metal nodes of metal-organic frameworks (MOFs) mimic the electronic environment of metalloenzyme active sites, but little is known about the reactivity of MOF nodes toward small molecules of biological relevance. Here, we report that the ferrous ions in Fe(2+)-exchanged MOF-5 disproportionate nitric oxide to produce nitrous oxide and a ferric nitrito complex. Although mechanistic studies of N-N bond forming transformations often invoke a hyponitrite species, as in nitric oxide reductase and NOx reduction catalysis, little is known about this intermediate in its monoanionic state. Together with the first report of N-N coupling between NO molecules in a MOF, we present evidence for a species that is consistent with a ferric hyponitrite radical, whose isolation is enabled by the spatial constraints of the MOF matrix.