A Model of Semimet Hemerythrin; NMR Spectroscopic Evidence of Valence Localization in Bis(μ‐carboxylato)(μ‐phenolato)diiron(II,III) Complexes in Solution

Abstract

A new hexadentate ligand 1 was used to prepare the first FeIIFeIII complex that mimics the unsymmetrical coordination in the active site of one form of semimet hemerythrin. The different valences of the iron ions in this model complex are localized in solution, in analogy to the iron centers in the protein.

Structural, EPR, and Mössbauer Characterization of (μ-Alkoxo)(μ-Carboxylato)Diiron(II,III) Model Complexes for the Active Sites of Mixed-Valent Diiron Enzymes

“…The Fe II -O bonds in 1 and 2 are significantly longer than those found in the corresponding diiron(II,II) complex [Fe II 2 ( N -Et-HPTB)(O 2 CPh)] 2+ (1.966(6) Å), where each iron center has trigonal bipyramidal geometry, 55 but they are in line with Fe(II)- μ -O bonds found in other diron(II,III) complexes such as [Fe II Fe III BPMP(O 2 CCH 2 CH 3 ) 2 ] 2+ (2.090(2) Å) 56 and [Fe II Fe III (tpdb)(O 2 CPh) 2 ] 2+ (2.088(7) Å). 43,47 The shorter lengths of the Fe III - μ -O (O1) bonds, on the other hand, compare favorably to those found for average Fe III - μ -O bond lengths in related diiron(III) complexes, such as [Fe III 2 (HPTB)(O 2 AsMe 2 )(Cl)(OH 2 )] 3+ (1.956(6) Å) and [Fe III 2 (HPTB)(OH)(ONO 2 ) 2 ] 2+ (1.965(8) Å). 57,58 Charge balance considerations also substantiate the mixed-valent diiron(II,III) assignment for both complexes.…”

“…The asymmetric coordination pattern observed for metal centers in 1 and 2 is uncommon for symmetric binucleating ligands which tend to bind two metal centers in a similar fashion. 43,44 It is unclear to us at this point why one isomer is favored over another.…”

Unsymmetrical Bimetallic Complexes with MII–(μ-OH)–MIII Cores (MIIMIII = FeIIFeIII, MnIIFeIII, MnIIMnIII): Structural, Magnetic, and Redox Properties

“…In many instances, these complexes utilize symmetric dinucleating ligands 5–7 or form coordinatively saturated geometries around each metal center. 8,9 We reported recently that the tetradentate sulfonamide-based tripodal ligand, N,N ′ ,N ″-[2,2′,2″-nitrilotris(ethane-2,1-diyl)]tris-(2,4,6-trimethylbenzene-sulfonamido), [MST] 3− , enforces a 5-coordinate geometry around a transition metal center and contains a second metal ion binding site to form heterobimetallic systems. Using this ligand complexes with [M II –(μ-OH)–M III ] cores (M II = Ca, Sr, Ba; M III = Mn, and Fe) were prepared from the activation of dioxygen.…”

Diiron(II) complexes showing a reversible oxygenation induced by a proton transfer mediated with a water molecule. Biological implication of a water molecule in hemerythrin function

“…Furthermore, it is quite unique that the differences between the redox potential values of Fe II Fe III /Fe III Fe III and Fe II Fe II /Fe II Fe III couples for 1-4, DE, are very close in comparison with those of diiron complexes reported hitherto[30,35,[40][41][42][43][44][45]. The smaller DE values in complexes 1-4 must have been induced by the protonation/deprotonation of the OH group of HTPPDO.…”