EDTA complexes Mossbauer

Isomer shift data obtained from Mossbauer spectral studies of Eu" and Dy " complexes of edta, salicylaldehydatoethylenedi-imine, and 8-hydroxy-quinoline have indicated that the covalent bonding in these species is small (ca. 4 % of the total) and is attributable to electron transfer from the ligands to the partly filled 4/ shell. 

Mossbauer effects studies of polypyrrole-iron EDTA and polypyrrole-tetrasulphonated iron phtalocyanine ppy(FePcTs) have been carried out by Saunders et al. [88,89]. These authors present a reasonable interpretation of the obtained Mossbauer data, however, in view of the complexity of the spectra, different line deconvolutions leading to different Mossbauer results are possible. 

Nonheme ferrous centers in some metalloproteins react reversibly with NO forming nitrosyl complexes with S = 312 characterized by the g values of about 4.0 and 2.0 [51]. The EPR spectrum of the nitrosylated NorR (abacterial NO-responsive transcription factor, the enhancer binding protein) is typical of a d high-spin Fe NO", where the S = 5/2 iron is antiferromagnetically coupled to the NO (Fig. 5, [52]). This is confirmed by the X-ray, resonance Raman, MCD, Mossbauer spectroscopies, and DFT calculations. Similar structures were proposed for the classical complexes, [Fe(NO)(l-isopropyl-4,7-(4-ferf-butyl-2mercaptobenzyl)-l,4, 7-triazacyclononane)], [53], Fe(EDTA)NO [54—56], the brown-ring compound, Fe(H20)5N0 [57], and for the Fe(N/V ,N -trimethyl-l,4,7-triazacyclononane) (N3)2N0 [54]. Interestingly, for the latter a spin equilibrium between the valence tautomers 5=1/2 and 3/2 in the solid state was observed. 

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