19 research outputs found
Formation Pathway of Roussin’s Red Ester (RRE) via the Reaction of a {Fe(NO)<sub>2</sub>}<sup>10</sup> Dinitrosyliron Complex (DNIC) and Thiol: Facile Synthetic Route for Synthesizing Cysteine-Containing DNIC
Transformation of {FeÂ(NO)<sub>2</sub>}<sup>10</sup> dinitrosyliron
complex (DNIC) FeÂ(CO)<sub>2</sub>(NO)<sub>2</sub> into [{FeÂ(NO)<sub>2</sub>}<sup>9</sup>]<sub>2</sub> Roussin’s red ester (RRE)
[(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>2</sub>)ÂFeÂ(NO)<sub>2</sub>]<sub>2</sub> (<b>3</b>) triggered by cysteamine via the reaction
pathway (intermediates) [{FeÂ(NO)<sub>2</sub>}<sup>10</sup>]<sub>2</sub>Â[(NO)<sub>2</sub>ÂFeÂ(μ-CO)Â(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>ÂNH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] (<b>1</b>) → {FeÂ(NO)<sub>2</sub>}<sup>9</sup>Â{FeÂ(NO)<sub>2</sub>}<sup>10</sup>Â[(NO)<sub>2</sub>FeÂ(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>ÂNH<sub>2</sub>)Â(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>ÂNH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] (<b>2</b>) → RRE <b>3</b> is demonstrated. The <b>1</b>-to-<b>2</b>-to-<b>3</b> conversion is promoted
by proton transfer followed by O<sub>2</sub> oxidation and deprotonation.
Additionally, a study on facile conversion of complex <b>3</b> to complexes [(SR)Â(SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] [SR = 2-aminoethanethiolate (<b>4</b>), benzenethiolate
(<b>5</b>)] and [(CysS))Â(SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] (<b>6</b>) via reaction with thiols
and the further utility of complex <b>5</b> as a template for
synthesizing mixed-thiolate-containing reduced RRE (rRRE) [(μ-SC<sub>6</sub>H<sub>5</sub>)Â(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>3</sub>)ÂFe<sub>2</sub>(NO)<sub>4</sub>] (<b>7</b>) provide
the methodology for the synthesis and isolation of neutral, pure cysteine-/mixed-thiolate-containing
DNIC/RRE. Compared to the conversion of complex <b>2</b> to
complex <b>3</b> via reaction with O<sub>2</sub>, diphenyl disulfide
triggers oxidation of complex <b>2</b> to lead to formation
of the neutral {FeÂ(NO)<sub>2</sub>}<sup>9</sup> DNIC <b>5</b> and RRE <b>3</b>. S–S bond activation of diphenyl disulfide
by rRRE <b>2</b> may support the decay (oxidation) of rRRE species
in ToMOC via the reduction of adjacent protein residues such as cystins,
proposed by Lippard
Formation Pathway of Roussin’s Red Ester (RRE) via the Reaction of a {Fe(NO)<sub>2</sub>}<sup>10</sup> Dinitrosyliron Complex (DNIC) and Thiol: Facile Synthetic Route for Synthesizing Cysteine-Containing DNIC
Transformation of {FeÂ(NO)<sub>2</sub>}<sup>10</sup> dinitrosyliron
complex (DNIC) FeÂ(CO)<sub>2</sub>(NO)<sub>2</sub> into [{FeÂ(NO)<sub>2</sub>}<sup>9</sup>]<sub>2</sub> Roussin’s red ester (RRE)
[(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>2</sub>)ÂFeÂ(NO)<sub>2</sub>]<sub>2</sub> (<b>3</b>) triggered by cysteamine via the reaction
pathway (intermediates) [{FeÂ(NO)<sub>2</sub>}<sup>10</sup>]<sub>2</sub>Â[(NO)<sub>2</sub>ÂFeÂ(μ-CO)Â(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>ÂNH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] (<b>1</b>) → {FeÂ(NO)<sub>2</sub>}<sup>9</sup>Â{FeÂ(NO)<sub>2</sub>}<sup>10</sup>Â[(NO)<sub>2</sub>FeÂ(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>ÂNH<sub>2</sub>)Â(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>ÂNH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] (<b>2</b>) → RRE <b>3</b> is demonstrated. The <b>1</b>-to-<b>2</b>-to-<b>3</b> conversion is promoted
by proton transfer followed by O<sub>2</sub> oxidation and deprotonation.
Additionally, a study on facile conversion of complex <b>3</b> to complexes [(SR)Â(SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] [SR = 2-aminoethanethiolate (<b>4</b>), benzenethiolate
(<b>5</b>)] and [(CysS))Â(SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>3</sub>)ÂFeÂ(NO)<sub>2</sub>] (<b>6</b>) via reaction with thiols
and the further utility of complex <b>5</b> as a template for
synthesizing mixed-thiolate-containing reduced RRE (rRRE) [(μ-SC<sub>6</sub>H<sub>5</sub>)Â(μ-SÂ(CH<sub>2</sub>)<sub>2</sub>NH<sub>3</sub>)ÂFe<sub>2</sub>(NO)<sub>4</sub>] (<b>7</b>) provide
the methodology for the synthesis and isolation of neutral, pure cysteine-/mixed-thiolate-containing
DNIC/RRE. Compared to the conversion of complex <b>2</b> to
complex <b>3</b> via reaction with O<sub>2</sub>, diphenyl disulfide
triggers oxidation of complex <b>2</b> to lead to formation
of the neutral {FeÂ(NO)<sub>2</sub>}<sup>9</sup> DNIC <b>5</b> and RRE <b>3</b>. S–S bond activation of diphenyl disulfide
by rRRE <b>2</b> may support the decay (oxidation) of rRRE species
in ToMOC via the reduction of adjacent protein residues such as cystins,
proposed by Lippard
Nitrite Activation to Nitric Oxide via One-fold Protonation of Iron(II)‑<i>O</i>,<i>O</i>‑nitrito Complex: Relevance to the Nitrite Reductase Activity of Deoxyhemoglobin and Deoxyhemerythrin
The reversible transformations [(Bim)<sub>3</sub>FeÂ(κ<sup>2</sup>-O<sub>2</sub>N)]Â[BF<sub>4</sub>] (<b>3</b>) ⇌ [(Bim)<sub>3</sub>FeÂ(NO)Â(κ<sup>1</sup>-ONO)]Â[BF<sub>4</sub>]<sub>2</sub> (<b>4</b>) were demonstrated and characterized.
Transformation of <i>O</i>,<i>O</i>-nitrito-containing
complex <b>3</b> into [(Bim)<sub>3</sub>FeÂ(μ-O)Â(μ-OAc)ÂFeÂ(Bim)<sub>3</sub>]<sup>3+</sup> (<b>5</b>) along with the release of
NO and H<sub>2</sub>O triggered by 1 equiv of AcOH implicates that
nitrite-to-nitric oxide conversion occurs, in contrast to two protons
needed to trigger nitrite reduction producing NO observed in the protonation
of [Fe<sup>II</sup>-nitro] complexes
Nitrite Activation to Nitric Oxide via One-fold Protonation of Iron(II)‑<i>O</i>,<i>O</i>‑nitrito Complex: Relevance to the Nitrite Reductase Activity of Deoxyhemoglobin and Deoxyhemerythrin
The reversible transformations [(Bim)<sub>3</sub>FeÂ(κ<sup>2</sup>-O<sub>2</sub>N)]Â[BF<sub>4</sub>] (<b>3</b>) ⇌ [(Bim)<sub>3</sub>FeÂ(NO)Â(κ<sup>1</sup>-ONO)]Â[BF<sub>4</sub>]<sub>2</sub> (<b>4</b>) were demonstrated and characterized.
Transformation of <i>O</i>,<i>O</i>-nitrito-containing
complex <b>3</b> into [(Bim)<sub>3</sub>FeÂ(μ-O)Â(μ-OAc)ÂFeÂ(Bim)<sub>3</sub>]<sup>3+</sup> (<b>5</b>) along with the release of
NO and H<sub>2</sub>O triggered by 1 equiv of AcOH implicates that
nitrite-to-nitric oxide conversion occurs, in contrast to two protons
needed to trigger nitrite reduction producing NO observed in the protonation
of [Fe<sup>II</sup>-nitro] complexes
Noticiero de Vigo : diario independiente de la mañana: Ano XXVIII Número 11586 - 1913 novembro 26
Insertion of CS<sub>2</sub> into
the thermally unstable nickelÂ(III)
hydride [PPN]Â[NiÂ(H)Â(PÂ(<i>o</i>-C<sub>6</sub>H<sub>3</sub>-3-SiMe<sub>3</sub>-2-S)<sub>3</sub>)] (<b>1</b>), freshly
prepared from the reaction of [PPN]Â[NiÂ(OC<sub>6</sub>H<sub>5</sub>)ÂPÂ(C<sub>6</sub>H<sub>3</sub>-3-SiMe<sub>3</sub>-2-S)<sub>3</sub>] and 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (HBpin; pin = OCMe<sub>2</sub>CMe<sub>2</sub>O) in tetrahydrofuran at −80 °C
via a metathesis reaction, readily affords [PPN]Â[Ni<sup>III</sup>(κ<sup>1</sup>-S<sub>2</sub>CH)Â(PÂ(<i>o</i>-C<sub>6</sub>H<sub>3</sub>-3-SiMe<sub>3</sub>-2-S)<sub>3</sub>)] (<b>2</b>) featuring
a κ<sup>1</sup>-S<sub>2</sub>CH moiety
Insight into the Reactivity and Electronic Structure of Dinuclear Dinitrosyl Iron Complexes
A combination of N/S/Fe K-edge X-ray
absorption spectroscopy (XAS), X-ray diffraction data, and density
functional theory (DFT) calculations provides an efficient way to
unambiguously delineate the electronic structures and bonding characters
of Fe–S, N–O, and Fe–N bonds among the direduced-form
Roussin’s red ester (RRE) [Fe<sub>2</sub>(μ-SPh)<sub>2</sub>(NO)<sub>4</sub>]<sup>2–</sup>(<b>1</b>) with
{FeÂ(NO)<sub>2</sub>}<sup>10</sup>-{FeÂ(NO)<sub>2</sub>}<sup>10</sup> core, the reduced-form RRE [Fe<sub>2</sub>(μ-SPh)<sub>2</sub>(NO)<sub>4</sub>]<sup>−</sup>(<b>3</b>) with {FeÂ(NO)<sub>2</sub>}<sup>9</sup>-{FeÂ(NO)<sub>2</sub>}<sup>10</sup> core, and
RRE [Fe<sub>2</sub>(μ-SPh)<sub>2</sub>(NO)<sub>4</sub>] (<b>4</b>) with {FeÂ(NO)<sub>2</sub>}<sup>9</sup>-{FeÂ(NO)<sub>2</sub>}<sup>9</sup> core. The major contributions of highest occupied molecular
orbital (HOMO) 113α/β in complex <b>1</b> is related
to the antibonding character between FeÂ(d) and FeÂ(d), FeÂ(d), and S
atoms, and bonding character between FeÂ(d) and NOÂ(Ï€*). The effective
nuclear charge (<i><i>Z</i></i><sub>eff</sub>)
of Fe site can be increased by removing electrons from HOMO to shorten
the distances of Fe···Fe and Fe–S from <b>1</b> to <b>3</b> to <b>4</b> or, in contrast, to
increase the Fe–N bond lengths from <b>1</b> to <b>3</b> to <b>4</b>. The higher IR ν<sub>NO</sub> stretching
frequencies (1761, 1720 cm<sup>–1</sup> (<b>4</b>), 1680,
1665 cm<sup>–1</sup> (<b>3</b>), and 1646, 1611, 1603
cm<sup>–1</sup> (<b>1</b>)) associated with the higher
transition energy of N<sub>1s</sub> →σ*Â(NO) (412.6 eV
(<b>4</b>), 412.3 eV (<b>3</b>), and 412.2 eV (<b>1</b>)) and the higher <i><i>Z</i></i><sub>eff</sub> of Fe derived from the transition energy of Fe<sub>1s</sub> →
Fe<sub>3d</sub> (7113.8 eV (<b>4</b>), 7113.5 eV (<b>3</b>), and 7113.3 eV (<b>1</b>)) indicate that the N–O bond
distances of these complexes are in the order of <b>1 > 3 >
4</b>. The N/S/Fe K-edge XAS spectra as well as DFT computations
reveal the reduction of complex <b>4</b> yielding complex <b>3</b> occurs at Fe, S, and NO; in contrast, reduction mainly occurs
at Fe site from complex <b>3</b> to complex <b>1</b>
Insight into the Reactivity and Electronic Structure of Dinuclear Dinitrosyl Iron Complexes
A combination of N/S/Fe K-edge X-ray
absorption spectroscopy (XAS), X-ray diffraction data, and density
functional theory (DFT) calculations provides an efficient way to
unambiguously delineate the electronic structures and bonding characters
of Fe–S, N–O, and Fe–N bonds among the direduced-form
Roussin’s red ester (RRE) [Fe<sub>2</sub>(μ-SPh)<sub>2</sub>(NO)<sub>4</sub>]<sup>2–</sup>(<b>1</b>) with
{FeÂ(NO)<sub>2</sub>}<sup>10</sup>-{FeÂ(NO)<sub>2</sub>}<sup>10</sup> core, the reduced-form RRE [Fe<sub>2</sub>(μ-SPh)<sub>2</sub>(NO)<sub>4</sub>]<sup>−</sup>(<b>3</b>) with {FeÂ(NO)<sub>2</sub>}<sup>9</sup>-{FeÂ(NO)<sub>2</sub>}<sup>10</sup> core, and
RRE [Fe<sub>2</sub>(μ-SPh)<sub>2</sub>(NO)<sub>4</sub>] (<b>4</b>) with {FeÂ(NO)<sub>2</sub>}<sup>9</sup>-{FeÂ(NO)<sub>2</sub>}<sup>9</sup> core. The major contributions of highest occupied molecular
orbital (HOMO) 113α/β in complex <b>1</b> is related
to the antibonding character between FeÂ(d) and FeÂ(d), FeÂ(d), and S
atoms, and bonding character between FeÂ(d) and NOÂ(Ï€*). The effective
nuclear charge (<i><i>Z</i></i><sub>eff</sub>)
of Fe site can be increased by removing electrons from HOMO to shorten
the distances of Fe···Fe and Fe–S from <b>1</b> to <b>3</b> to <b>4</b> or, in contrast, to
increase the Fe–N bond lengths from <b>1</b> to <b>3</b> to <b>4</b>. The higher IR ν<sub>NO</sub> stretching
frequencies (1761, 1720 cm<sup>–1</sup> (<b>4</b>), 1680,
1665 cm<sup>–1</sup> (<b>3</b>), and 1646, 1611, 1603
cm<sup>–1</sup> (<b>1</b>)) associated with the higher
transition energy of N<sub>1s</sub> →σ*Â(NO) (412.6 eV
(<b>4</b>), 412.3 eV (<b>3</b>), and 412.2 eV (<b>1</b>)) and the higher <i><i>Z</i></i><sub>eff</sub> of Fe derived from the transition energy of Fe<sub>1s</sub> →
Fe<sub>3d</sub> (7113.8 eV (<b>4</b>), 7113.5 eV (<b>3</b>), and 7113.3 eV (<b>1</b>)) indicate that the N–O bond
distances of these complexes are in the order of <b>1 > 3 >
4</b>. The N/S/Fe K-edge XAS spectra as well as DFT computations
reveal the reduction of complex <b>4</b> yielding complex <b>3</b> occurs at Fe, S, and NO; in contrast, reduction mainly occurs
at Fe site from complex <b>3</b> to complex <b>1</b>
Nitrate-to-Nitrite-to-Nitric Oxide Conversion Modulated by Nitrate-Containing {Fe(NO)<sub>2</sub>}<sup>9</sup> Dinitrosyl Iron Complex (DNIC)
Nitrosylation of high-spin [FeÂ(κ<sup>2</sup>-O<sub>2</sub>NO)<sub>4</sub>]<sup>2<b>–</b></sup> (<b>1</b>) yields {FeÂ(NO)}<sup>7</sup> mononitrosyl iron complex (MNIC) [(κ<sup>2</sup>-O<sub>2</sub>NO)Â(κ<sup>1</sup>-ONO<sub>2</sub>)<sub>3</sub>FeÂ(NO)]<sup>2<b>–</b></sup> (<b>2</b>)
displaying an <i>S</i> = 3/2 axial electron paramagnetic
resonance (EPR) spectrum (<i>g</i><sub>⊥</sub> =
3.988 and <i>g</i><sub>∥</sub> = 2.000). The thermally
unstable nitrate-containing {FeÂ(NO)<sub>2</sub>}<sup>9</sup> dinitrosyl
iron complex (DNIC) [(κ<sup>1</sup>-ONO<sub>2</sub>)<sub>2</sub>FeÂ(NO)<sub>2</sub>]<sup><b>–</b></sup> (<b>3</b>) was exclusively obtained from reaction of HNO<sub>3</sub> and [(OAc)<sub>2</sub>FeÂ(NO)<sub>2</sub>]<sup><b>–</b></sup> and was
characterized by IR, UV–vis, EPR, superconducting quantum interference
device (SQUID), X-ray absorption spectroscopy (XAS), and single-crystal
X-ray diffraction (XRD). In contrast to {FeÂ(NO)<sub>2</sub>}<sup>9</sup> DNIC [(ONO)<sub>2</sub>FeÂ(NO)<sub>2</sub>]<sup><b>–</b></sup> constructed by two monodentate O-bound nitrito ligands, the
weak interaction between Fe(1) and the distal oxygens O(5)/O(7) of
nitrato-coordinated ligands (Fe(1)···O(5) and Fe(1)···O(7)
distances of 2.582(2) and 2.583(2) Ã…, respectively) may play
important roles in stabilizing DNIC <b>3</b>. Transformation
of nitrate-containing DNIC <b>3</b> into N-bound nitro {FeÂ(NO)}<sup>6</sup> [(NO)Â(κ<sup>1</sup>-NO<sub>2</sub>)ÂFeÂ(S<sub>2</sub>CNEt<sub>2</sub>)<sub>2</sub>] (<b>7</b>) triggered by bisÂ(diethylthiocarbamoyl)
disulfide ((S<sub>2</sub>CNEt<sub>2</sub>)<sub>2</sub>) implicates
that nitrate-to-nitrite conversion may occur via the intramolecular
association of the coordinated nitrate and the adjacent polarized
NO-coordinate ligand <b>(</b>nitrosonium<b>)</b> of the
proposed {FeÂ(NO)<sub>2</sub>}<sup>7</sup> intermediate [(NO)<sub>2</sub>(κ<sup>1</sup>-ONO<sub>2</sub>)ÂFeÂ(S<sub>2</sub>CNEt<sub>2</sub>)<sub>2</sub>] (<b>A</b>) yielding {FeÂ(NO)}<sup>7</sup> [(NO)ÂFeÂ(S<sub>2</sub>CNEt<sub>2</sub>)<sub>2</sub>] (<b>6</b>) along with
the release of N<sub>2</sub>O<sub>4</sub> (·NO<sub>2</sub>) and
the subsequent binding of ·NO<sub>2</sub> to complex <b>6</b>. The N-bound nitro {FeÂ(NO)}<sup>6</sup> complex <b>7</b> undergoes
Me<sub>2</sub>S-promoted O-atom transfer facilitated by imidazole
to give {FeÂ(NO)}<sup>7</sup> complex <b>6</b> accompanied by
release of nitric oxide. This result demonstrates that nitrate-containing
DNIC <b>3</b> acts as an active center to modulate nitrate-to-nitrite-to-nitric
oxide conversion
Insight into One-Electron Oxidation of the {Fe(NO)<sub>2</sub>}<sup>9</sup> Dinitrosyl Iron Complex (DNIC): Aminyl Radical Stabilized by [Fe(NO)<sub>2</sub>] Motif
A reversible redox reaction ({FeÂ(NO)<sub>2</sub>}<sup>9</sup> DNIC
[(NO)<sub>2</sub>FeÂ(NÂ(Mes)Â(TMS))<sub>2</sub>]<sup>−</sup> (<b>4</b>) ⇄ oxidized-form DNIC [(NO)<sub>2</sub>FeÂ(NÂ(Mes)Â(TMS))<sub>2</sub>] (<b>5</b>) (Mes = mesityl, TMS = trimethylsilane)),
characterized by IR, UV–vis, <sup>1</sup>H/<sup>15</sup>N NMR,
SQUID, XAS, single-crystal X-ray structure, and DFT calculation, was
demonstrated. The electronic structure of the oxidized-form DNIC <b>5</b> (<i>S</i><sub>total</sub> = 0) may be best described
as the delocalized aminyl radical [(NÂ(Mes)Â(TMS))<sub>2</sub>]<sub>2</sub><sup>–•</sup> stabilized by the electron-deficient
{Fe<sup>III</sup>(NO<sup>–</sup>)<sub>2</sub>}<sup>9</sup> motif,
that is, substantial spin is delocalized onto the [(NÂ(Mes)Â(TMS))<sub>2</sub>]<sub>2</sub><sup>–•</sup> such that the highly
covalent dinitrosyl iron core (DNIC) is preserved. In addition to
IR, EPR (<i>g</i> ≈ 2.03 for {FeÂ(NO)<sub>2</sub>}<sup>9</sup>), single-crystal X-ray structure (Fe–NÂ(O) and N–O
bond distances), and Fe K-edge pre-edge energy (7113.1–7113.3
eV for {FeÂ(NO)<sub>2</sub>}<sup>10</sup> vs 7113.4–7113.9 eV
for {FeÂ(NO)<sub>2</sub>}<sup>9</sup>), the <sup>15</sup>N NMR spectrum
of [FeÂ(<sup>15</sup>NO)<sub>2</sub>] was also explored to serve as
an efficient tool to characterize and discriminate {FeÂ(NO)<sub>2</sub>}<sup>9</sup> (δ 23.1–76.1 ppm) and {FeÂ(NO)<sub>2</sub>}<sup>10</sup> (δ −7.8–25.0 ppm) DNICs. To the
best of our knowledge, DNIC <b>5</b> is the first structurally
characterized tetrahedral DNIC formulated as covalent–delocalized
[{Fe<sup>III</sup>(NO<sup>–</sup>)<sub>2</sub>}<sup>9</sup>–[NÂ(Mes)Â(TMS)]<sub>2</sub><sup>–•</sup>]. This
result may explain why all tetrahedral DNICs containing monodentate-coordinate
ligands isolated and characterized nowadays are confined in the {FeÂ(NO)<sub>2</sub>}<sup>9</sup> and {FeÂ(NO)<sub>2</sub>}<sup>10</sup> DNICs
in chemistry and biology
Insight into One-Electron Oxidation of the {Fe(NO)<sub>2</sub>}<sup>9</sup> Dinitrosyl Iron Complex (DNIC): Aminyl Radical Stabilized by [Fe(NO)<sub>2</sub>] Motif
A reversible redox reaction ({FeÂ(NO)<sub>2</sub>}<sup>9</sup> DNIC
[(NO)<sub>2</sub>FeÂ(NÂ(Mes)Â(TMS))<sub>2</sub>]<sup>−</sup> (<b>4</b>) ⇄ oxidized-form DNIC [(NO)<sub>2</sub>FeÂ(NÂ(Mes)Â(TMS))<sub>2</sub>] (<b>5</b>) (Mes = mesityl, TMS = trimethylsilane)),
characterized by IR, UV–vis, <sup>1</sup>H/<sup>15</sup>N NMR,
SQUID, XAS, single-crystal X-ray structure, and DFT calculation, was
demonstrated. The electronic structure of the oxidized-form DNIC <b>5</b> (<i>S</i><sub>total</sub> = 0) may be best described
as the delocalized aminyl radical [(NÂ(Mes)Â(TMS))<sub>2</sub>]<sub>2</sub><sup>–•</sup> stabilized by the electron-deficient
{Fe<sup>III</sup>(NO<sup>–</sup>)<sub>2</sub>}<sup>9</sup> motif,
that is, substantial spin is delocalized onto the [(NÂ(Mes)Â(TMS))<sub>2</sub>]<sub>2</sub><sup>–•</sup> such that the highly
covalent dinitrosyl iron core (DNIC) is preserved. In addition to
IR, EPR (<i>g</i> ≈ 2.03 for {FeÂ(NO)<sub>2</sub>}<sup>9</sup>), single-crystal X-ray structure (Fe–NÂ(O) and N–O
bond distances), and Fe K-edge pre-edge energy (7113.1–7113.3
eV for {FeÂ(NO)<sub>2</sub>}<sup>10</sup> vs 7113.4–7113.9 eV
for {FeÂ(NO)<sub>2</sub>}<sup>9</sup>), the <sup>15</sup>N NMR spectrum
of [FeÂ(<sup>15</sup>NO)<sub>2</sub>] was also explored to serve as
an efficient tool to characterize and discriminate {FeÂ(NO)<sub>2</sub>}<sup>9</sup> (δ 23.1–76.1 ppm) and {FeÂ(NO)<sub>2</sub>}<sup>10</sup> (δ −7.8–25.0 ppm) DNICs. To the
best of our knowledge, DNIC <b>5</b> is the first structurally
characterized tetrahedral DNIC formulated as covalent–delocalized
[{Fe<sup>III</sup>(NO<sup>–</sup>)<sub>2</sub>}<sup>9</sup>–[NÂ(Mes)Â(TMS)]<sub>2</sub><sup>–•</sup>]. This
result may explain why all tetrahedral DNICs containing monodentate-coordinate
ligands isolated and characterized nowadays are confined in the {FeÂ(NO)<sub>2</sub>}<sup>9</sup> and {FeÂ(NO)<sub>2</sub>}<sup>10</sup> DNICs
in chemistry and biology