Iron complexes diamagnetic

Magnetic Interaction in a Diamagnetic Iron Complex (Example [Fe02(SC6HF4)(TPpiyP)])... 

The electronic absorption spectra of the products of one-electron electrochemical reduction of the iron(III) phenyl porphyrin complexes have characteristics of both iron(II) porphyrin and iron(III) porphyrin radical anion species, and an electronic structure involving both re.sonance forms Fe"(Por)Ph] and tFe "(Por—)Ph has been propo.sed. Chemical reduction of Fe(TPP)R to the iron(II) anion Fe(TPP)R) (R = Et or /7-Pr) was achieved using Li BHEt3 or K(BH(i-Bu)3 as the reductant in benzene/THF solution at room temperature in the dark. The resonances of the -propyl group in the F NMR spectrum of Fe(TPP)(rt-Pr) appear in the upfield positions (—0.5 to —6.0 ppm) expected for a diamagnetic porphyrin complex. This contrasts with the paramagnetic, 5 = 2 spin state observed... 

One-electron reduction of the iron(lll) alkyl complexes forms the diamagnetic iron(ll) alkyl anions [Fe(Por)R. The iron(ll) anions do not react with oxygen directly, but are first oxidized by O2 to the corresponding alkyliron(III) complexes, Fe(Por)R, which then insert O2 as described above. 

Diazoalkanes are u.seful is precursors to ruthenium and osmium alkylidene porphyrin complexes, and have also been investigated in iron porphyrin chemistry. In an attempt to prepare iron porphyrin carbene complexes containing an oxygen atom on the /(-carbon atom of the carbene, the reaction of the diazoketone PhC(0)C(Ni)CH3 with Fe(TpCIPP) was undertaken. A low spin, diamagnetic carbene complex formulated as Fe(TpCIPP)(=C(CH3)C(0)Ph) was identified by U V-visible and fI NMR spectroscopy and elemental analysis. Addition of CF3CO2H to this rapidly produced the protonated N-alkyl porphyrin, and Bit oxidation in the presence of sodium dithionitc gave the iron(II) N-alkyl porphyrin, both reactions evidence for Fe-to-N migration processes. ... 

The use of pyridine as solvent dramatically alters the spectral properties of the iron complex of octamethylcorrole. Such a spectrum is reported in Fig. 20 and pertinent data in Table 12. The three resonances (A-C) observed at low field have been attributed to the methyl substituents, the fourth resonance probably being located in the diamagnetic region obscured by the solvent resonances. 

The determination of n from measurement of peff is the most familiar application of magnetic susceptibility measurements to inorganic chemists. To the extent that the spin-only formula is valid, it is possible to obtain the oxidation state of the central atom in a complex. Thus an iron complex with a peff of 5.9B.M. certainly contains Fe(III) (high-spin d5) and not Fe(II). The diamagnetism of AgO rules out its formulation as silver(II) oxide, because Ag2+ has an odd number of electrons (d9) and should be paramagnetic it contains Ag(I) and Ag(III), in equal amounts. There are, however, a number of pitfalls, especially if reliance is placed on a single measurement at room temperature. The Curie law is rarely obeyed within the limits of experimental error. This means that the measured peff is somewhat temperature-dependent. A number of factors can be responsible for deviations from ideal Curie (or even Curie-Weiss) behaviour, and/or from the spin-only formula. 

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). 

The best known of the low-spin iron complexes are undoubtedly the cyanides, and considerable Mossbauer data have now been collected. The diamagnetic... 

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