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 NO 1775 s, 1716 vs, 1668 vs cm -1 (THF)] between two adjacent [Fe(NO) 2 ] groups implicate the electron delocalization nature of the singly O -phenoxide-bridged dinuclear dinitrosyliron complex (DNIC) [Fe(NO) 2 (μ-ON 2 Me )Fe(NO) 2 ] ( 1 ). Electronic interplay between [Fe(NO) 2 ] units and [ON 2 Me ] - ligand in DNIC 1 rationalizes that "hard" O -phenoxide moiety polarizes iron center(s) of [Fe(NO) 2 ] unit(s) to enforce a "constrained" π-conjugation system acting as an electron reservoir to bestow the spin-frustrated {Fe(NO) 2 } 9 -{Fe(NO) 2 } 9 -[ · ON 2 Me ] 2- electron configuration ( S total = 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) 2 ] 10 unit, while preserving the {Fe(NO) 2 } 9 core in DNICs {Fe(NO) 2 } 9 -[ · ON 2 Me ] 2- [K-18-crown-6-ether)][(ON 2 Me )Fe(NO) 2 ] ( 2 ) and {Fe(NO) 2 } 9 -[ · ON 2 Me ] [(ON 2 Me )Fe(NO) 2 ][PF 6 ] ( 3 ). Electrochemical studies suggest that the redox interconversion among [{Fe(NO) 2 } 9 -[ · ON 2 Me ] 2- ] DNIC 3 ↔ [{Fe(NO) 2 } 9 -[ON 2 Me ] - ] ↔ [{Fe(NO) 2 } 9 -[ · ON 2 Me ]] DNIC 2 are kinetically feasible, corroborated by the redox shuttle between O-bridged dimerized [(μ-ON Me ) 2 Fe 2 (NO) 4 ] ( 4 ) and [K-18-crown-6-ether)][(ON Me )Fe(NO) 2 ] ( 5 ). In parallel with this finding, the electronic structures of [{Fe(NO) 2 } 9 -{Fe(NO) 2 } 9 -[ · ON 2 Me ] 2- ] DNIC 1 , [{Fe(NO) 2 } 9 -[ · ON 2 Me ] 2- ] DNIC 2 , [{Fe(NO) 2 } 9 -[ · ON 2 Me ]] DNIC 3 , [{Fe(NO) 2 } 9 -[ON Me ] - ] 2 DNIC 4, and [{Fe(NO) 2 } 9 -[ · ON Me ] 2- ] DNIC 5 are evidenced by EPR, SQUID, and Fe K-edge pre-edge analyses, respectively.