Electronic Structure Modulation in an Exceptionally Stable Non‐Heme Nitrosyl Iron(II) Spin‐Crossover Complex

We present the synthesis, properties, and characterization of [Fe(T1Et4iPrIP)(NO)(H2O)2](OTf)2 (1) {T1Et4iPrIP = Tris(1‐ethyl‐4‐isopropyl‐imidazolyl)phosphine} as a model for the nitrosyl adduct of gentisate 1,2‐dioxygenase (GDO). The further characterization of [Fe(T1Et4iPrIP)(THF)(NO)(OTf)](OTf) (2) which was previously communicated (Inorg. Chem. 2014, 53, 5414) is also presented. The weighted average Fe–N–O angle of 162° for 1 is very close to linear (≥ 165°) for these types of complexes. The coordinated water ligands participate in hydrogen bonding interactions. The spectral properties (EPR, UV/Vis, FTIR) for 1 are compared with 2 and found to be quite comparable. Complex 1 closely follows the relationship between the Fe–N–O angle and NO vibrational frequency which was previously identified for six‐coordinate {FeNO}7 complexes. Liquid FTIR studies on 2 indicate that the ν(NO) vibration position is sensitive to solvent shifting to lower energy (relative to the solid) in donor solvent THF and shifting to higher energy in dichloromethane. The basis for this behavior is discussed. The Keq for NO binding in 2 was calculated in THF and found to be 470 m–1. Density functional theory (DFT) studies on 1 indicate donation of electron density to the iron center from the π* orbitals of formally NO–. Such a donation accounts for the near linearity of the Fe–N–O bond and the large ν(NO) value of 1791 cm–1.

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“…Recent studies on {FeNO} 7 complexes that undergo spin‐crossover also appear to confirm the trend shown in Figure , …”

Section: Resultssupporting

confidence: 62%

A Structural Model for the Iron–Nitrosyl Adduct of Gentisate Dioxygenase

Banerjee

Speelman

et al. 2018

Eur J Inorg Chem

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“…This description has been the subject of several studies using different levels of theory. The estimation of T 1/2 is reasonably close to experimental results for Fe(II) and Fe (III) compounds . (See Table S6 and Figure S2).…”

Section: Resultsmentioning

confidence: 99%

“…With an adequate description of the LS and HS states, provided by TPSS functional we proceeded to reproduce the experimental spin transition curves observed in the series of complexes. A methodology that has been used to this end by some authors is to treat the thermal spin crossover as a thermodynamic equilibrium between LS and HS states. The change in Gibbs free energy between these two states ( ΔG HL ) at a certain temperature is related to the equilibrium constant ( K HL =γ HS /γ LS ).…”

Section: Resultsmentioning

confidence: 99%

“…However, an adequate study of the SCO transition requires firstly a correct estimation of the electronic properties that determine the HS‐LS gap and secondly, the geometry changes ( Δ r HL ) mentioned above. Once again, the B3LYP functional is one of the most widely used, despite the good results achieved by the TPSSh hybrid functional, in particular in the calculation of ΔE 0 HL and its use in the determination of spin transition curves …”

Section: Determination Of Redox and Magnetic Propertiesmentioning

confidence: 99%

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Correlating Properties in Iron(III) Complexes: A DFT Description of Structure, Redox Potential and Spin Crossover Phenomena

et al. 2017

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Calculations of structure, redox potential and spin transition energies were performed using DFT approximations for a series of [Fe(bztpen)OR] 2 + / + type Fe III /Fe II systems (R=Me, Et, nPr, nBu), which have a temperature dependent spin crossover behavior. These compounds exhibit changes in redox and magnetic properties, related to structural variations quite important for their possible applications among which signal generator materials stand out. Functionals B3LYP, wB97XÀD and TPSS along with PCM solvation model were evaluated for redox potential, whereas for spin crossover the TPSSh functional was also included. The multireference character of these compounds was tested as well. Calculations were compared to experimental measurements, and wB97XÀD proved able to accurately describe the geometries observed in solid state for the low spin (LS) and high spin (HS) states; moreover, it had the best correlation between calculated and experimental redox potential values. However, in the description of the spin transition energies the TPSS functional is needed to correctly describe the LS state as the observed ground state in the complexes at low temperature, which allows to calculate proper spin transition curves as a function of temperature. From these results, we obtained suitable approximations for an accurate description of redox potential and magnetic properties for the Fe III coordination compounds, which can be extended to model similar systems.

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“…With weak field ligands, especially polypyridine and related ligand systems with other N-heterocycles, hs-{FeNO} 7 complexes usually result. In rare cases, for example by using salen-type ligands, complexes can also be obtained that show a spin-crossover and exist in the hs and ls state as a function of temperature. − Here, distinct temperature-dependent changes in ν(N–O), magnetic moment and physical properties are observed. Other such examples include complexes that change spin state upon variation of a coligand, for example by different solvent coordination conditions .…”

Section: Non-heme Iron Centers and Nomentioning

confidence: 99%

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

et al. 2021

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Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

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Electronic Structure Modulation in an Exceptionally Stable Non‐Heme Nitrosyl Iron(II) Spin‐Crossover Complex

Cited by 15 publications

References 61 publications

A Structural Model for the Iron–Nitrosyl Adduct of Gentisate Dioxygenase

A Structural Model for the Iron–Nitrosyl Adduct of Gentisate Dioxygenase

Correlating Properties in Iron(III) Complexes: A DFT Description of Structure, Redox Potential and Spin Crossover Phenomena

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

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