Electronic Structure and Transformation of Dinitrosyl Iron Complexes (DNICs) Regulated by Redox Non-Innocent Imino-Substituted Phenoxide Ligand.

The coupled NO-vibrational peaks [IR ν 1775 s, 1716 vs, 1668 vs cm (THF)] between two adjacent [Fe(NO)] groups implicate the electron delocalization nature of the singly -phenoxide-bridged dinuclear dinitrosyliron complex (DNIC) [Fe(NO)(μ-ON)Fe(NO)] (). Electronic interplay between [Fe(NO)] units and [ON] ligand in DNIC rationalizes that "hard" -phenoxide moiety polarizes iron center(s) of [Fe(NO)] unit(s) to enforce a "constrained" π-conjugation system acting as an electron reservoir to bestow the spin-frustrated {Fe(NO)}-{Fe(NO)}-[ON] electron configuration ( = 1/2). This system plays a crucial role in facilitating the ligand-based redox interconversion, working in harmony to control the storage and redox-triggered transport of the [Fe(NO)] unit, while preserving the {Fe(NO)} core in DNICs {Fe(NO)}-[ON] [K-18-crown-6-ether)][(ON)Fe(NO)] () and {Fe(NO)}-[ON] [(ON)Fe(NO)][PF] (). Electrochemical studies suggest that the redox interconversion among [{Fe(NO)}-[ON]] DNIC ↔ [{Fe(NO)}-[ON]] ↔ [{Fe(NO)}-[ON]] DNIC are kinetically feasible, corroborated by the redox shuttle between O-bridged dimerized [(μ-ON)Fe(NO)] () and [K-18-crown-6-ether)][(ON)Fe(NO)] (). In parallel with this finding, the electronic structures of [{Fe(NO)}-{Fe(NO)}-[ON]] DNIC , [{Fe(NO)}-[ON]] DNIC , [{Fe(NO)}-[ON]] DNIC , [{Fe(NO)}-[ON]] DNIC and [{Fe(NO)}-[ON]] DNIC are evidenced by EPR, SQUID, and Fe K-edge pre-edge analyses, respectively.