Relative Binding Affinity of Thiolate, Imidazolate, Phenoxide, and Nitrite Toward the {Fe(NO)2} Motif of Dinitrosyl Iron Complexes (DNICs): The Characteristic Pre-Edge Energy of {Fe(NO)2}9 DNICs

Tsai, Mi Ching; Tsai, Fu-Te; Lu, Tsai‐Te; Tsai, Mei-Ling; Wei, Yin-Ching; Hsu, I‐Jui; Lee, Jyh‐Fu; Liaw, Wen‐Feng

doi:10.1021/ic901675p

Cited by 68 publications

(99 citation statements)

References 60 publications

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“…Subsequently, a convenient, one-pot synthesis of this dissymmetric diiron complex (Fig. 2a) made use of the reaction of Fe(CO) 3 (NO) À as precursor to a (proposed) transient Fe(CO) 2 (NO) 2 þ species that readily releases CO and NO, the latter accounting for the (bmedach)Fe(NO) unit 21 . This in situ production of both parts of the bimetallic complex suggested thermodynamic stability for 1 þ , a common requisite shared by many practical molecular electrocatalysts.…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

Redox active iron nitrosyl units in proton reduction electrocatalysis

et al. 2014

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Base metal, molecular catalysts for the fundamental process of conversion of protons and electrons to dihydrogen, remain a substantial synthetic goal related to a sustainable energy future. Here we report a diiron complex with bridging thiolates in the butterfly shape of the 2Fe2S core of the [FeFe]-hydrogenase active site but with nitrosyl rather than carbonyl or cyanide ligands. This binuclear [(NO)Fe(N 2 S 2 )Fe(NO) 2 ] þ complex maintains structural integrity in two redox levels; it consists of a (N 2 S 2 )Fe(NO) complex (N 2 S 2 ¼ N,N 0 -bis(2-mercaptoethyl)-1,4-diazacycloheptane) that serves as redox active metallodithiolato bidentate ligand to a redox active dinitrosyl iron unit, Fe(NO) 2 . Experimental and theoretical methods demonstrate the accommodation of redox levels in both components of the complex, each involving electronically versatile nitrosyl ligands. An interplay of orbital mixing between the Fe(NO) and Fe(NO) 2 sites and within the iron nitrosyl bonds in each moiety is revealed, accounting for the interactions that facilitate electron uptake, storage and proton reduction.

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Section: Synthesis and Characterizationmentioning

confidence: 99%

Redox active iron nitrosyl units in proton reduction electrocatalysis

et al. 2014

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“…The presence in M-DNIC of two nitrosyl and two sulfur-containing ligands and the tetrahedral spatial structure of these complexes in the crystal state were confirmed by X-ray diffraction analysis data [54, 66–68]. However, the tetrahedral field of these ligands cannot induce pairing of the spins in the d 7 configuration to the low-spin ( S = 1/2) state even under conditions of its strong distortion [54].…”

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confidence: 98%

“…Two alternative models of M-DNIC have been developed according to which the low-spin ( S = 1/2) state of M-DNIC is determined by antiferromagnetic interaction between the iron atom and two nitrosyl ligands. In the framework of the first model, the structure of the DNIC core appears as [Fe 3+ (NO − ) 2 ] (or as {Fe(NO) 2 } 9 according to Enemark-Feltham classification) and has a high-spin ( S = 5/2) d 5 -configuration of the iron atom and a triplet ( S = 1) state of nitroxyl ligands [68, 69]. According to the second model, DNIC with a core structure [Fe + (NO) 2 ] {Fe(NO) 2 } 9 (in terms of Enemark-Feltham's classification) is characterized by a high-spin (S = 3/2) d 7 -configuration of the iron atom bound to two neutral NO molecules ( S = 1/2) [66, 67].…”

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confidence: 99%

“…In the meantime, the equation proposed in [73] can be used for estimating the values of the g -factor tensor of the EPR signal of DNIC, namely, the one having a [Fe + (NO) 2 ] core. According to the authors, the low-spin ( S = 1/2) state of this core is provided by the antiferromagnetic interaction of Fe + with a high-spin ( S = 3/2) d 7 configuration and nitrosyl NO ligands (S = 1/2) with the overall spin S = 1 [67, 68]. Such a spin-paired system can be regarded as a mixed triad of interchanging magnetic centers, namely, two identical M* (two NO molecules) and one M # (iron ion) (provided the exchange interaction is ≫ of the quantum energy of the microwave electromagnetic field of the EPR radiospectrometer), and the value of the g -factor for this triad cluster described by the following equation [73] can be calculated as:

\begin{matrix} g = g_{3} + \frac{(g_{3} - g_{i}) [S_{3} (S_{3} + 1) - S_{1,2} (S_{1,2} + 1) - S (S + 1)]}{2 S (S + 1)}, \end{matrix}

where g i ( g i = g 1 = g 2 ) is the g-factor tensor of the EPR signal characteristic of both identical magnetic centers of M* (two NO molecules), S 1,2 is the total spin of these centers equal to unity, g 3 is the g-tensor and S 3 is the spin of the magnetic center M # (iron ion) equal to 3/2 and S is the total spin of triad cluster equal to 1/2.…”

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confidence: 99%

“…Let us consider now the model of DNIC with a configuration of {Fe(NO) 2 } 9 and a [Fe 3+ (NO − ) 2 ] core [66, 68, 69]. Their low-spin ( S = 1/2) state is provided by antiferromagnetic interaction between iron in the high-spin ( S = 5/2) state and a d 5 electronic configuration and nitrosyl ligands of NO − in the triplet state ( S = 1).…”

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Electronic and Spatial Structures of Water-Soluble Dinitrosyl Iron Complexes with Thiol-Containing Ligands Underlying Their Ability to Act as Nitric Oxide and Nitrosonium Ion Donors

Vanin

Burbaev

2011

Journal of Biophysics

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The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe+(NO+)2] core ({Fe(NO)2}7 according to the Enemark-Feltham classification). Similarly, the {(RS−)2Fe+(NO+)2}+ structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d7 electron configuration of the iron atom and predominant localization of the unpaired electron on MO(dz2) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

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