Year: 2026
Type: preprint
Abstract: Dinitrosyl iron complexes (DNICs) are prevalent NO-derived iron species; yet the factors that govern their formation at non-heme iron centers remain poorly understood. Here, we show that secondary-sphere hydrogen bonding interaction, together with steric accessibility of the Fe center enables quantitative formation of a {Fe(NO)2}9 (1-DNIC) complex through a previously unrecognized NO-driven redox pathway. Reaction of [Fe(DIG2dien)]2+ (DIG2dien = N-methyl-bis[2-(N,N′-diisopropylguanidino)ethyl]amine) with NO gas affords [Fe(DIG2dien)(NO)2]+ (1-DNIC) as the sole detectable iron-containing product. Spectroscopic and computational characterization by Mössbauer, EPR, SQUID, IR, X-ray absorption spectroscopy and DFT calculation establish an S = 1/2 ground state and a hydrogen-bond-supported {Fe(NO)2}9 unit. Mechanistic studies support a self-sustaining pathway in which NO functions as both a nitrosylating agent and a reductant, thereby circumventing the stoichiometric constraints of the previously reported disproportionation mechanisms. Notably, the sterically hindered analogue [Fe(DIG3tren)]2+ (2, DIG3tren = tris(N’,N”-diisopropylguanidinyl-2-ethyl)amine) reacts with NO gas to form the linear, hydrogen-bonded {FeNO}7 complex [Fe(DIG3tren)(NO)]2+ (2-NO) rather than a DNIC. Furthermore, 1-DNIC transfers NO to the ferrous precursor 2, generating 2-NO with concomitant formation of trace N2O. These findings establish secondary-sphere hydrogen bonding as a key determinant of DNIC assembly and reveal a hydrogen-bond-mediated, NO-driven mechanism for quantitative DNIC formation at a non-heme iron center.
Source: ChemRxiv
Institution: Humboldt-Universität zu Berlin
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7207629456