A iron-dinitrosyl species (L-6)Fe(NO)(2) (2), generated from nitrogen monoxide (center dot NO) binding to its related iron (II)-mononitrosyl complex (L-6)Fe(NO) (1), efficiently effects reductive coupling of two center dot NO molecules to release nitrous oxide (N2O), when Cu-center dot ion and 2 equiv acid are added; the heme/Cu product is [(L-6)Fe-III center dot center dot center dot Cu-II (D)](3 center dot) (D = H2O or MeCN). In a control experiment where only (L-6)Fe(NO)(2) (2) is exposed to 2 equiv acid, no UV-vis change is observed; upon warming, center dot NO(g) is released and (L-6)Fe(NO) is reformed. The copper ion complex within the IL ligand framework is required for the center dot NO coupling chemistry. In a further control experiment Cu-center dot ion is added to (L-6)Fe(NO)(2) without acid present, [(L-6)Fe(NO)center dot center dot center dot Cu-II(NO2-)](+) is obtained, with the amount of N2O(g) reteased fitting with copper(I) ion promoted disproportionation chemistry, 3 center dot NO + ligand-Cu-1 -> N2O + tigand-Cu-II (NO2-). The chemical system described represents a (stoichiometric) functional modet for heme/Cu protein nitric oxide reductase activity