Unusual Synthetic Pathway for an {Fe(NO)2}9Dinitrosyl Iron Complex (DNIC) and Insight into DNIC Electronic Structure via Nuclear Resonance Vibrational Spectroscopy

• DOI: 10.1021/acs.inorgchem.6b00510
• Publication Date: 2016-05-22T03:51:23Z
• Authors: Amy L. Speelman; Bo Zhang; Alexey Silakov; Kelsey M. Skodje; E. Ercan Alp; Jiyong Zhao; Michael Y. Hu; Eunsuk Kim; Carsten Krebs; Nicolai Lehnert
• Keywords: Oxidation state

Dinitrosyl iron complexes (DNICs) are among the most abundant NO-derived cellular species. Monomeric DNICs can exist in {Fe(NO)2}9 or {Fe(NO)2}10 oxidation state (in Enemark–Feltham notation). However, experimental studies of analogous both states rare, which prevents a thorough understanding differences electronic structures these Here, DNIC [Fe(dmp)(NO)2](OTf) (1; dmp = 2,9-dimethyl-1,10-phenanthroline) is synthesized from ferrous precursor via an unusual pathway, involving disproportionation {FeNO}7 complex to yield and ferric species, subsequently reduced by NO gas generate that re-enters reaction cycle. In contrast with neutral N-donor ligands, 1 exhibits high solution stability be characterized structurally spectroscopically. Reduction yields corresponding [Fe(dmp)(NO)2] (2). The Mössbauer isomer shift 2 0.08 mm/s smaller than 1, indicates center slightly more oxidized complex. nuclear resonance vibrational spectra (NRVS) distinct provide direct insight into bonding complexes. particular, symmetric out-of-plane Fe–N–O bending mode shifted higher energy 188 cm–1 comparison 1. Using quantum chemistry centered normal coordinate analysis (QCC-NCA), this shown arise increase Fe–NO bond order stiffening Fe(NO)2 unit upon reduction 2. DFT calculations demonstrate changes iron-centered leads π-back-bonding complexes, agreement all findings. Finally, implications structure for their reactivity discussed, especially respect N–N formation reductases.