Utilizing the proton-responsive pyridinediimine ligand [(2,6-PrCH)(N[double bond, length as m-dash]CMe)(N(Pr)CH)(N[double bond, length as m-dash]CMe)CHN] (didpa), the ligand-based reduction of nitrate (NO) to nitric oxide (NO) was achieved. The bioinspired [Fe(Hdidpa)(CO)] was shown to react with tetrabutylammonium nitrate to form the dinitrosyl iron complex [Fe(didpa)(NO)]. The didpa scaffold was shown to provide two electrons for the net reduction of NO to NO in 43% yield.

A series of pyridinediimine (PDI) iron complexes that contain a pendant 15-crown-5 located in the secondary coordination sphere were synthesized and characterized. The complex Fe((15c5)PDI)(CO)2 (2) was shown in both the solid state and solution to encapsulate redox-inactive metal ions. Modest shifts in the reduction potential of the metal-ligand scaffold were observed upon encapsulation of either Na(+) or Li(+).

The proton-responsive pyridinediimine ligand, (DEA)PDI (where (DEA)PDI = [(2,6-(i)PrC6H3)(N[double bond, length as m-dash]CMe)(N(Et)2C2H4)(N[double bond, length as m-dash]CMe)C5H3N]) was utilized for the reduction of NO2(-) to NO. Nitrite reduction is facilitated by the protonated secondary coordination sphere coupled with the ligand-based redox-active sites of [Fe(H(DEA)PDI)(CO)2](+) and results in the formation of the {Fe(NO)2}(9) DNIC, [Fe((DEA)PDI)(NO)2](+).