Fe III complex of

The preparation and characterization, and Mossbauer and epr spectra of Fe(II) and Fe(III) complexes of cyclopentadienyldithiocarboxy-late have been reported recently (261). 

The Fe(III) complexes of R-substituted salicylaldehyde thiosemicarbazone (R-thsa2- Fig. 6) are among the most studied spin crossover materials of this family. The crystal structures of several of them have been determined at various temperatures. The iron-donor atom distances are compiled in Table 2. The Fe(III) ion is in a distorted FeS2N202 octahedron formed by two thiosemicarbazone ligands, which are geometrically arranged in such a way that the S and O atoms are located in cis positions, whereas the N atoms occupy trans positions, i.e. each tridentate molecule coordinates in an equatorial plane [101]. 

The Fe(III) complexes of the dianion of pyruvic acid thiosemicarbazone (thpu2- Fig. 7), (cation+)[Fe(thpu)2]-nH20, are very similar to those of the salicylaldehyde derivatives (Fig. 6) discussed above. The spin state properties are quite sensitive to changes in the counter-cation (typically an alkali-metal cation or a protonated nitrogenous base) and the lattice water content of the material. The parent compound, NH4[Fe(thpu)2], is low spin at room temperature [113]. Li[Fe(thpu)2]-3H20 is also low spin but K[Fe(thpu)2] 2-H20 shows almost complete spin crossover between 80 and 300 K [108]. 

Fig. 26. X-ray crystal structure of the Fe(III) complex of the antimalarial chelator desferrioxamine 108. Adapted from (542). 

Homonuclear correlation spectroscopy (COSY) experiments (see Chapter 9) substantiate the theoretical predictions, based on molecular orbital calculation, of the pattern of spin delocalization in the 3e orbitals of low-spin Fe(III) complexes of unsymmetrically substituted tetraphenylporphyrins [46]. Furthermore, the correlations observed show that this n electron spin density distribution is differently modified by the electronic properties of a mono-orf/io-substituted derivative, depending on the distribution of the electronic effect over both sets of pyrrole rings or only over the immediately adjacent pyrrole rings [46]. No NOESY cross peaks are detectable, consistently with expectations of small NOEs for relatively small molecules and effective paramagnetic relaxation [47]. 

Effect of Pressure on Proton-Coupled Electron Transfer Reactions of Seven-Coordinate Iron Complexes in Aqueous Solution It has been shown that seven-coordinate Fe(III) diaqua complexes consisting of a pentaaza macrocyclic ligand possess superoxide dismutase (SOD) activity, and therefore could serve an imitative SOD function.360 Choosing appropriate chemical composition of a chelate system yielded suitable pKa values for the two coordinated water molecules so that the Fe(III) complexes of 2,6-diacetylpyridine-bis(semicarbazone) (dapsox) and 2,6-diacetylpyridine-bis(semioxamazide) (dapsc) (see Scheme 7.12) would be present principally in the highly active aqua-hydroxo form in solution at physiological pH.361... 

The absence of a detectable 13C03 signal from the paramagnetic Fe(III) complex of transferrin probably reflects broadening caused by... 

The chelation effect of Cys-X-Y-Cys was also found for the MCD spectra of Fe(III) complexes of Z-Cys-Pro-Leu-Cys-OMe or Z-Cys-Ala-Ala-Cys-OMe, which exhibited a characteristic ligand-metal charge transfer (LMCT) at 350 nm, but not for those of the Fe(III) complex of Z-Ala-Cys-OMe, Z-Cys-Ala-Cys-OMe, or S2-o-xyl (28). The MCD spectral differences in the region of 300-400 nm are related to the difference in the electronic states of the Fe(III) singly occupied metal t2 orbitals affected by the lone pair on the sulfur atom. The possibility of a spectroscopic splitting by a specific Cys-thiolate orientation relative to other Fe-S bondings has been predicted theoretically by Bair and Goddard (29). The orientation of n orbitals of the sulfur lone pair is now found to be determined by the peptide conformation which dictates the steric disposition of the S-C bond. 

The crystal structure of the purple Fe(III) complex of 3-hydroxyflavone (45) has an octahedral coordination sphere with a 1 2 Fe(III)-to-fiavone ratio and a Cl ion at an axial position". Similar to the Cu(II) complexes, the Fe(III)-0(enolate) bond distances (1.935 and 1.981 A) are significantly shorter than the Fe(III)-0(keto) bond distances (2.136 and 2.119 A). The Fe(III) center has a rhombic magnetic environment based on EPR studies. Complete cleavage of pUC18 plasmid DNA by this Fe(III)-flavonoid complex (30 p,M) took place in 15 minutes in the presence 1 equivalent of ascorbate/H202 and was still observable without ascorbate, which is attributed to the reduction capability of the bound flavonoid to yield Fe(II) and initiate the oxidative DNA cleavage" . 

Hydroxyflavone and its derivatives form a-ketoenolate (L) complexes with metals (M) of ML, ML2 and ML3 stoichiometry (Section in.B.l.b). Since QD from various sources can be activated by different metal ions, the catalysis of QD has been mimicked with mononuclear Mn(II) and Fe(III) complexes of flavonols, Mn(II)(L)2(py)2 and Fe(ni)(L)3. Upon exposure of these complexes to dioxygen at 95 °C, CO production and the formation of the 0-benzoylsalicylic acid methylester can be detected with GC-MS, analogous to the products found with QD catalysis. Using ca 60% 02 in the thermal... 

Hirano T, Hirobe M, Kobayashi K, Odani A, Yamauchi O, Ohsawa M, Satow Y, Nagano T. (2000) Mechanism of superoxide dismutase-like activity of Fe(ll) and Fe(III) complexes of tetrakis-N,N,N ,N (2-pyridylmethyl)ethylenedi-amine. Chemioal and Pharmaoeutieal Bulletin 48 223-230. 

Hydroxyl radical OH Photolysis of hydroxo or other Fe(III) complexes of NOJ, NO2 decomposition of O3, photolysis of H2O2... 

The oxygen complex can be drawn like this or, alternatively, as an Fe(III) complex of an oxyanion (below). 

The Wieghardt study discussed earlier (9) also encompassed the preparation of an acetato-bridged Fe(III) complex of 1 (n = 2). Such... 

The initial study focused on second-sphere coordination between Fe(III) complexes of deferriferrioxamine-B,... 

Pluth MD, Lippard SJ (2012) Reversible binding of nitric oxide to an Fe(III) complex of a tetra-amido macrocycle. Chem Commun (Camb) 48 11981-11983... 

Kuroda et r//.reported a cyclodextrin-sandwiched poiphyrin 109. The Fe(III) complex of this poiphyrin binds benzylmercaptan in an aqueou.s buffer solution at pH 7.0. Two molecules of benzylmercaptan were bound consecutively, with the first a.s.sociation constant larger than 10 M and the second association constant being 7 X lO M "The host also binds adamantanecarboxylate. a typical guest for cyclodextrin, with a binding constant of 7 X 10 M-. ... 

Kelleher, W.J., Krueger, R.J. and Rosazza, J.P. (1971) The violet pigment of lysergic acid alkaloiD-producing cultures of Claviceps paspali Fe(III) complex of 2, 3-dihydroxybenzoic acid. Lloydia, 34,188-194. 

Hemoglobin contains four iron-porphyrin sites each capable of binding one O2. Each site consists of an Fe(II) held within a porphyrin ring via coordination to the four N donors. The fifth Fe coordination position is occupied by a histidine, called the proximal His. The sixth site of the octahedral Fe(II) normally interacts with O2. which binds reversibly in the bent form. One electron is transferred from Fe(II) to O2 so that the O2 adduct is best considered as an Fe(III) complex of superoxide ion (Oa"). Unfortunately, the blood contains a small concentration of CO, formed in the biological degradation of the porphyrin ring. As a result, about... 

Iron alkynyl complexes containing aromatic moieties are of particular interest as building blocks for molecular devices. Second-order non-linear optical properties have been investigated for various Fe(ii) and Fe(iii) complexes of the type [(dppe)Gp Fe(G=G-Ar)] where Ar = pyridine, GsH4N(GH3), or/>-G6H4X (X = NO2, GN, GF3, H, OMe, and NH2). These compounds have shown significant quadratic redox-switchable polarizabilities. Further examples of redox-active iron alkynyl synthons containing aromatic units have been reported, where the iron alkynyl unit is... 

Ce02. To use the electrodeposition of Fe304 as an example of the electrodeposition of metal oxides using the redox method, the material can be produced by electrochemically reducing a Fe(III) complex of triethanolamine (TEA) as shown in Equations 17.1 and... 

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