Studies on the Reaction of Iron(II) with NO in a Noncoordinating Ionic Liquid

Abstract

In an earlier study we investigated the reaction of iron(II) chloride with NO in a strongly coordinating ionic liquid 1-ethyl-3-methylimidazolium dicyanamide [emim][dca] and showed that the actual reactive species in solution was [Fe(II)(dca)5Cl](4-). For the present report we investigated in detail how this reaction could proceed in a noncoordinating ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate [emim][OTf]. The donor ability of OTf(-) is much lower than that of dca(-), such that the solubility of FeCl2 in [emim][OTf] strongly depended on other donors like water or chloride ions present or added to the ionic liquid. On increasing the chloride concentration in [emim][OTf], the tetrachloridoferrate complex [emim]2[FeCl4] was formed, as verified by X-ray crystallography. This complex undergoes reversible binding of NO, for which the UV-vis spectral characteristics of the green-brown nitrosyl product resembled that found for the corresponding nitrosyl complexes formed in water and [emim][dca] as solvents. A detailed analysis of the spectra revealed that the {Fe-NO}(7) species has Fe(II)-NO(•) character in contrast to Fe(III)-NO(-) as found for the other solvents. The formation constant, however, is much higher than in [emim][dca], lying closer to the value found for water as solvent. Surprisingly, the Mössbauer spectrum found in [emim][OTf] is very unusual and unsimilar to that found in water and [emim][dca] as solvents, pointing at a different electron density distribution between Fe and NO in {Fe-NO}.7 First, the high isomer shift points to the presence of iron(II) species in solution, thus indicating that upon NO binding no oxidation to iron(III) occurs. Second, the negligible quadrupole splitting suggests a high local symmetry around the iron center. The nitrosyl product is suggested to be [Fe(II)Cl3NO](-), which is supported by electron paramagnetic resonance (EPR) and IR measurements. The nature of the Fe(II) complexes formed in [emim][OTf] depends on the additives required to dissolve FeCl2 in this ionic liquid.

{FeNO}7‐Type Halogenido Nitrosyl Ferrates: Syntheses, Bonding, and Photoinduced Linkage Isomerism

“…The absorption bands A and B of the visible region are typical for high‐spin‐{FeNO} 7 chromophores in general, be it in an aqueous environment such as the “brown‐ring” complex or in an ionic liquid . Though the spectral features of the brown or green solutions are long known, an assignment of the absorption bands has remained ambiguous.…”

On the real catalytically active species for CO2 fixation into cyclic carbonates under near ambient conditions: Dissociation equilibrium of [BMIm][Fe(NO)2Cl2] dependant on reaction temperature

“…These IR frequencies are comparable to those reported for (Et4N)[FeCl2(NO)2] (1765 and 1692 cm -1 ), thus suggesting that similar DNIC {[Fe(NO)2Cl2] -} species are present in both complexes. [73,74] In addition, the IR data reported in the literature for other iron-nitrosyl complexes [79] support the presence of an iron species formally written as {Fe III −(NO − )2}. For high-spin iron-nitrosyl complexes, the strength of the Fe−NO and N−O bonds is strongly influenced by the effective nuclear charge on iron.…”

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

“…Equation was employed to fit the empirical data. The study revealed the equilibrium constant ( K eq ) to be 470 m –1 which is comparable to values found in similar studies …”

“…The study revealed the equilibrium constant (K eq ) to be 470 M -1 which is comparable to values found in similar studies. [36] (1)…”