Reduction of aqueous nitrite (NO2–) to gaseous nitric oxide (NO) is significant to both the global nitrogen cycle (GNC) and human physiology. It is a proton-coupled electron transfer process (NO2– + 2H+ + e– -> NO + H2O) that is catalyzed by bacterial nitrite reductase (NiR) at the heme center. Without NiR present in mammals, heme proteins are proposed to catalyze NO2– reduction to NO endogenously under hypoxic conditions. The inherent reactivity of coordinated NO2– at ferrous hemes generally leads to NO, but NO is trapped by another ferrous heme and stable {FeNO}7 (Enemark-Feltham notation) complexes. Inspired by cytochrome cd1 NiR, we aim to establish the requirements for catalytic NO2– reduction to NO by synthesizing nonheme Fe(II) complexes containing neutral-charge, nitrogen-rich ligand constructs with vacant, solvent-bound axial coordination positions. NO2– as a strong π-acceptor has a strong binding affinity to Fe(II) via the nitrogen atom (nitro isomer), generating LS Fe(II)-nitro complexes. The same first coordination sphere among these nonheme Fe(II)-nitro complexes leads to similar structures, electronic properties, and reactivities. Upon the addition of 2H+/e–, Fe(II)-nitro complexes are reduced to NO and regenerate the corresponding Fe(II)-solvato complexes, indicating the catalytic capability. In addition, when proton-responsive functionalities are incorporated on the ligand constructs, the protonated form results in H-bonds with the bound nitro, termed as the second coordination sphere. The resulting second-sphere interactions significantly alter the reactivities of complexes and moderately enhance the rate of NO2– reduction. For example, the second-sphere interactions also trigger ligand-based NO2– reduction to NO when the redox-active iron(II) center is replaced to a redox-inactive zinc(II) center. However, the decomposition of the ligand using this zinc complex makes NO2– reduction stoichiometric, which reflects the important roles of the redox-active iron center in catalysis. Herein, synthesis, properties, and the reactivities of nonheme iron(II)-nitro complexes are demonstrated for the development of NO2– reduction catalysts. This dissertation reveals mechanistic insights towards NO release, contributing to the balance of the GNC and mammalian vasodilation.