Nitric oxide disproportionation at the site-isolated Fe centers of the metal organic framework material known as Fe-MOF-5 has been explored with density functional theory (DFT). The computed reaction sequence supports the mechanism suggested by experiment that involves the formation of the monoanionic hyponitrite radical. The validity of the computed reaction mechanism is bolstered by impressive agreement between computed and experimental vibrational spectroscopic evidence of each reaction step. Similarly the analogous MnII-MOF-5 system indicates that the disproportionation of NO should proceed smoothly with this single-site material. These results, observed also for some homogeneous Mn(II) catalysts, indicate that heterogeneous Mn-based materials could be employed as efficient biological and industrial catalytic systems in NO disproportionation processes.