A detailed investigation into the electronic structures of macrocyclic iron(II)-nitrosyl compounds and their similarities to ferrous heme-nitrosyls

► Five-coordinate ferrous-nitrosyl complexes with macrocyclic Schiff base ligands. ► Good models for five-coordinate ferrous heme-nitrosyls. ► NO serves as a strong σ donor and medium strong π acceptor ligand. ► The optical (UV-Vis and MCD) spectra of the complexes are assigned. ► TD-DFT calculations predict metal → π∗(NO) transitions in the UV region.