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

Wun-Yan Wu; Wei-Yuan Zheng; Wei-Ting Chen; Fu-Te Tsai; Ming-Li Tsai; Chih-Wen Pao; Jeng-Lung Chen; Wen-Feng Liaw

doi:10.1021/acs.inorgchem.3c03367

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

Inorg Chem. 2024 Feb 5;63(5):2431-2442. doi: 10.1021/acs.inorgchem.3c03367. Epub 2024 Jan 23.

Authors

Wun-Yan Wu¹, Wei-Yuan Zheng¹, Wei-Ting Chen¹, Fu-Te Tsai¹, Ming-Li Tsai², Chih-Wen Pao³, Jeng-Lung Chen³, Wen-Feng Liaw¹

Affiliations

¹ Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
² Department of Chemistry, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.
³ National Synchrotron Radiation Research Center, Hsinchu 30013, Taiwan.

Abstract

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-ON₂^Me)Fe(NO)₂] (1). Electronic interplay between [Fe(NO)₂] units and [ON₂^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-[^·ON₂^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-[^·ON₂^Me]^2- [K-18-crown-6-ether)][(ON₂^Me)Fe(NO)₂] (2) and {Fe(NO)₂}⁹-[^·ON₂^Me] [(ON₂^Me)Fe(NO)₂][PF₆] (3). Electrochemical studies suggest that the redox interconversion among [{Fe(NO)₂}⁹-[^·ON₂^Me]^2-] DNIC 3 ↔ [{Fe(NO)₂}⁹-[ON₂^Me]^-] ↔ [{Fe(NO)₂}⁹-[^·ON₂^Me]] DNIC 2 are kinetically feasible, corroborated by the redox shuttle between O-bridged dimerized [(μ-ON^Me)₂Fe₂(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-[^·ON₂^Me]^2-] DNIC 1, [{Fe(NO)₂}⁹-[^·ON₂^Me]^2-] DNIC 2, [{Fe(NO)₂}⁹-[^·ON₂^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.