Asymmetry within the Fe(NO)2 moiety of dithiolate dinitrosyl iron complexes

•DNICs with thiol ligands {Fe(NO)2}7–10 were examined by several levels of theory.•Asymmetry within the Fe(NO)2 moiety was found persistent in all structures.•Pathways leading to putative hyponitrite adducts were also investigated.•The results relate the geometrical asymmetries to NO donation mechanism in DNICs.

Dinitrosyl iron complexes have earned attention due to their applications as nitric oxide donors as well as their interesting electronic structures. Typical Fe–NO electromerism issues are complicated in this case by the presence of a second nitrosyl ligand. Each of the formal oxidation states of iron in such complexes – from Fe(III) to Fe(0) – have been shown to be subject to electromerism. Here, broken-symmetry density functional theory data are shown, that reveal asymmetry within iron dithiolate dinitrosyl models in several formal oxidation states. CASSCF calculations on selected models confirm the multiconfigurational character of the Fe(NO)2 moiety, with the largest contributor at only 44% of the total weight of the wave function. This asymmetry is most noticeable in the excited states; it is further enhanced by solvation and reveals itself even in the ground state in dynamics calculations as well as in reaction pathways connecting the dinitrosyl state to a putative hyponitrite adduct.

Graphical abstractAsymmetry within the Fe(NO)2 moiety detected by DFT CASSCF and AIMD is the key for nitric oxide donation mechanism by DNICs.Figure optionsDownload full-size imageDownload as PowerPoint slide