Iron complexes electronic spectra

Diels-Alder reactions, 4, 842 flash vapour phase pyrolysis, 4, 846 reactions with 6-dimethylaminofuKenov, 4, 844 reactions with JV,n-diphenylnitrone, 4, 841 reactions with mesitonitrile oxide, 4, 841 structure, 4, 715, 725 synthesis, 4, 725, 767-769, 930 theoretical methods, 4, 3 tricarbonyl iron complexes, 4, 847 dipole moments, 4, 716 n-directing effect, 4, 44 2,5-disubstituted synthesis, 4, 116-117 from l,3-dithiolylium-4-olates, 6, 826 electrocyclization, 4, 748-750 electron bombardment, 4, 739 electronic deformation, 4, 722-723 electronic structure, 4, 715 electrophilic substitution, 4, 43, 44, 717-719, 751 directing effects, 4, 752-753 fluorescence spectra, 4, 735-736 fluorinated derivatives, 4, 679 H NMR, 4, 731 Friedel-Crafts acylation, 4, 777 with fused six-membered heterocyclic rings, 4, 973-1036 fused small rings structure, 4, 720-721 gas phase UV spectrum, 4, 734 H NMR, 4, 7, 728-731, 939 solvent effects, 4, 730 substituent constants, 4, 731 halo... 

Chemically the iron complex 18 is reduced by K/Na alloy in THF to give a green solution of the salt 57. The d7 anion in 57 has been characterized by its ESR spectrum in frozen solution (62). Similarly, on treatment with sodium amalgam, the cobalt complexes 7 and 13 yield dark brownish-red solutions of 58 and 59, respectively. A surprisingly robust PPh4+ salt 60 (mp 158-159°C) could be isolated. Solution and solid state magnetic measurements confirm the presence of two unpaired electrons in these 20-e species as in NiCp2 (60). 

S-Donor ligands. As an extension of previous studies on related complexes of iron(n), cobalt(n), nickel(n), and zinc(n), the structure of Mn[SPPh2-N PPh2S]2 has been determined by X-ray methods. The metal atom is co-ordinated in an approximately tetrahedral manner by the four sulphur atoms. The two MnS2P2N rings adopt the twisted boat conformation with S and P atoms at the apices. The single-crystal electronic spectrum has been measured and interpreted.92... 

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique to explore the electronic state of iron complexes. EPR spectroscopy of the non-heme iron component in the electron transfer system of mitochondria has been extensively used and discussed by Beinert (9), who showed that this type of iron has a so-called g = 1.94 type signal upon reduction. Consideration of the EPR spectrum of adrenodoxin has been described previously (68). 

Phthalocyaninato(2-)] iron(II) is a dark blue, thermally stable solid that can be sublimed in vacuo at 300°. It is very soluble in pyridine, giving deep blue solutions of the bis(pyridine) adducts. It also forms an unstable purple hexaaniline adduct when dissolved in aniline. It is soluble in concentrated sulfuric add and dimethyl sulfoxide (slightly) but is insoluble in most other organic solvents. The iron(II) complex, unlike the corresponding iron(II) porphines, is relatively stable toward oxidation to the iron (III) state. The electronic spectrum shows the following absorption bands (1-chloronaphthalene solution) 595 (e = 16,000), 630 (e = 17,000), 658 (e = 63,000) (pyridine solution) 333 (e = 45,000), 415 (e = 15,000), 395 (e = 2000), 658 nm (e = 8000). 

Given the similarities in chemical shifts and linewidths, as well as the contributions of symmetry to the appearance of the spectrum, the electronic and molecular structure of new iron complexes of N-alkyl-porphyrins may be ascertained, to a first approximation, from NMR data. Thus for low-spin iron(III) complexes one would expect at least four sharp resonances upfield of the diamagnetic region. Iron(IV) complexes should have at least four resonances upfield of the diamagnetic region. Iron(III) can be differentiated from iron(IV) by measurement of the solution susceptibility (51). 

Individual iron atoms in Prussian blue appear to have well-defined electronic configurations with lifetimes of around 10-7 seconds. An interpretation295 of the electronic spectrum suggests that the blue colour arises from electron transfer between the [Fe(CN)6]4 and iron(III) ions and that the relevant electrons reside on the ferrocyanide moiety in the ground state. Vacuum pyrolysis of Prussian blue can result in valence reversal to give296 iron(II) ferricyanide, which has also been identified297 in aqueous solution, the complex previously thought to have been Turnbull s blue . 

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

Other spectroscopic techniques that have been used in the study of dppf complexes are XPS, UPS [43] and UV/VIS spectroscopy. XPS provides useful complementary information on the differentiation of pendant and coordinated phosphines [42,80]. Caution needs to be exercised, however, as P(2p) core binding energy is not very sensitive towards changes in the ligand coordination mode or the oxidation state of the metal [42]. The electronic absorption spectra of dppf and MCl2(dppf-P, P ) complexes (M = Co, Ni, Pd, Pt, Zn, Cd, Hg) exhibit an easily detected band at 405—465 nm, attributed to a transition in the ferrocenyl moiety [43]. The presence of any iron-to-metal bonding is usually indicated by an intense ct - a transition [21], as evident in the electronic spectrum of [Pd(dppf-P,P )(PPh3)][BF4]2, 3 [40]. 

The electronic spectrum of the B2 subunit ( ax = 455, 485, and 615 nm) closely resembles those of Mn-catalase and synthetic tribridged Mn 0 complexes (8). The metal site was thus proposed (229) to be analogous to the diiron center of the enzyme from E. coli. This analogy may be reasonable as iron restores 50-70% of the activity in protein derived from Mn-deprived cells (230). Similar to the enzyme from E. coli, the Mn-containing ribonucleotide reductase is inhibited by hydroxyurea and au-... 

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