High-valent iron complexes with tetraamido macrocyclic ligands: Structures, Mössbauer spectroscopy, and DFT calculations

Chanda, Arani; Popescu, D.; Oliveira, Filipe Tiago de; Bominaar, Emile L.; Ryabov, Alexander D.; Münck, Eckard; Collins, Terrence J.

doi:10.1016/j.jinorgbio.2005.12.016

Cited by 78 publications

(54 citation statements)

References 48 publications

(68 reference statements)

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“…12 and Table 1) that differs distinctly from that of 3 indicating significantly more positive δ=0.25(3) mm s −1 (Δδ=0.13 mm s −1 ), indicating a metal-centred reduction resulting in the formation of the low-spin (S=1/2) ferric species12144749. Smaller |Δ E Q | value (1.12 (6) mm s −1 ) compared with that in 3 (2.505 (5) mm s −1 ) can be explained by the appearance of a positive valence contribution to the EFG and thus to Δ E Q caused by adding one electron into the , d xy level12161747. The negative terms of covalence contribution to the EFG are approximately equal for iron(IV) and iron(III) complexes (as in both corresponding three-dimensional configurations the d xz and d yz orbitals, giving rise to the negative covalence contribution, are formally empty).…”

Section: Resultsmentioning

confidence: 93%

“…In search of ligand systems that provide an extraordinarily efficient stabilization of high-valent iron, we have been inspired by TAML-based complexes, as they are among the most stable high-valent iron species reported up to date (in particular, in aqueous solution)12131415161718192021. The deprotonated amide groups are known to be one of the best donors for the stabilization of high oxidation states of transitional metals.…”

Section: Resultsmentioning

confidence: 99%

“…As the valence contribution to the electric field gradient (EFG) for 3d configuration ( z 2 ) 2 ( x 2 − y 2 ) 1 ( xy ) 1 is zero3747, the large negative Δ E Q can be explained by noticeable negative covalence contribution because of electron density donation from the hydrazido groups into the d xz and d yz orbitals (the electrons in , d xz and d yz orbitals yield a negative contribution to Δ E Q (refs 12, 16, 17). …”

Section: Resultsmentioning

confidence: 99%

“…One of the most spectacular examples of such compounds is a family of iron complexes based on a class of the tetraamide macrocyclic ligands (Fe-TAMLs) developed by Collins since the early 1990s (refs 12, 13, 14, 15, 16, 17). Fe-TAML systems demonstrate not only remarkable stability and resistance to oxidative degradation but can also act as exceptionally efficient homogeneous catalysts in aqueous solutions exploiting high-valent iron oxo species1819.…”

mentioning

confidence: 99%

“…Ferrates(VI), considered for a long time as probably the most stable among known high-valent iron compounds, decompose upon standing in aqueous solution within hours, evolving molecular oxygen40. Evidently, the most efficient systems providing extended lifetimes in aqueous media are high-valent Fe-TAMLs12141516.…”

mentioning

confidence: 99%

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Indefinitely stable iron(IV) cage complexes formed in water by air oxidation

et al. 2017

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In nature, iron, the fourth most abundant element of the Earth's crust, occurs in its stable forms either as the native metal or in its compounds in the +2 or +3 (low-valent) oxidation states. High-valent iron (+4, +5, +6) compounds are not formed spontaneously at ambient conditions, and the ones obtained synthetically appear to be unstable in polar organic solvents, especially aqueous solutions, and this is what limits their studies and use. Here we describe unprecedented iron(IV) hexahydrazide clathrochelate complexes that are assembled in alkaline aqueous media from iron(III) salts, oxalodihydrazide and formaldehyde in the course of a metal-templated reaction accompanied by air oxidation. The complexes can exist indefinitely at ambient conditions without any sign of decomposition in water, nonaqueous solutions and in the solid state. We anticipate that our findings may open a way to aqueous solution and polynuclear high-valent iron chemistry that remains underexplored and presents an important challenge.

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