Infrared spectra of Fe

Iron(II) complexes are often included in studies when complexes are prepared from a large number of different metal ions. 2-formylpyridine thiosemicarbazone, 5, forms brown [Fe(5)2A2] (A = Cl, Br) when prepared in ethanol and [Fe(5-H)2] from aqueous alcohol solution [156], All of these complexes are diamagnetic. The resonance Raman and infrared spectra of [Fe(5-H)2] were examined in detail [130] and coordination occurs via the pyridyl nitrogen, azomethine nitrogen and thiol sulfur. There is appreciable d-d sulfur-to-iron(II) Jt-bonding. Solution studies of iron(II) complexes of some 5-substituted-2-formylpyridine thiosemicarbazones have been reported [157], but no solids... 

The metal isotope technique has been used to study the effect of magnetic crossover on the low-frequency spectrum of Fe(phen)2(NCS)2. This compound exists as a high-spin complex at 298 K and as a low-spin complex a( lOO K. Figure 111-12 shows the infrared spectra of Fe(phen)2(NCS)2 obtained by Takemolo and Hutchinson. On the basis of observed isotopic shifts, along... 

In Fe(CO)5 the formal charge on iron is —5, and in Cr(CO)6 the formal charge on chromium is —6. We should expect that the back donation would be more extensive in either of these compounds than it is in the case of Ni(CO)4. Because the greater back donation results in a greater reduction in C-O bond order, the infrared spectra of these compounds should show this effect. The positions of the CO stretching bands for these compounds are as follows ... 

A remarkable result is the position of (Proto-DME) between (TPP) and (TpivPP) in Series b, Table 15. The vco values originate from various sources and the observed differences between the three porphyrins may thus be meaningless. (Note the enormous solvent dependence of the infrared spectra of various hemes that has been reported recently (29).) Anyway, the three porphyrins have approximately the same ir-acceptor capacity. Therefore, the tetraarylporphyrin moiety, especially in the picket fence hemes, e.g., Fe(TpivPP)LX [33], is comparable with the natural hemes Fe(Proto-DME)LX ([14], M = Fe), and its use as a model porphyrin for the study of hemoprotein properties is well justified, despite the very different substitution pattern. 

In their original paper (2) on the structure of Fe5C(CO)l5, Dahl and co-workers assigned two bands in the infrared spectrum of hydrocarbon solutions of the cluster, at 790 and 770 cm-1, to vFeC modes. This assignment has been confirmed by a recent study of the infrared spectra of the series M5C(CO)15, (M = Fe, Ru, Os) (78). The room temperature spectra of the compounds (Table II) in the solid state are quite similar to each other, comprising three bands assigned as the a, and e modes (split in the solid state) expected for the C4 symmetry of the isostructural clusters. At low temperature the ruthenium and osmium clusters exhibit five absorptions associated with M-C stretches, whereas the iron cluster retains its room temperature spectrum. This is ascribed to the presence of two types of cluster molecule in the crystal lattices of the ruthenium and osmium clusters which are isostructural with, but not isomorphous with, the iron analog in which all the molecules are identical. 

Figure 10.2 Absorption spectra of Fe(III) oxides in the ultraviolet-visible region (left) and visible-near-infrared region (right) (from Sherman Waite, 1985). (a) Goethite (b) lepidocrocite (c) maghemite and (d) hematite. Measured reflectance spectra were converted into absorption spectra by applications of the Kebulka-Munk function. The vertical bars indicate band positions (listed in table 10.2).

Resonance Raman (Xexcit = 647 nm) and mid-infrared spectra of the cyanide-bridged model compounds display three isotope-dependent vibrational modes. Two vibrations (2182 and 535 cm ) show monotonic decreases with increasing mass of the cyanide ligand and could thus be assigned to the C-N stretch and Fe-CN-Cu stretch, respectively. The C-N stretch was also observed by resonance Raman for the first time. The third vibration, detected with resonance Raman, showed a zigzag-type behavior (495,487,493,485 cm ) with the isotopomers that... 

Although (maleic acid)Fe(C0)4 has a symmetry plane perpendicular to the plane of the double bond, (fumaric acid)Fe(C0)4 is clearly asymmetric and should thus be capable of resolution into its enantiomers (457). Accordingly, addition of the complex to a solution of brucine in acetone and crystallization of the diastereoisomeric salts followed by decomposition with hydrochloric acid yielded the two enantiomers having optical activities [a]ff —593 (acetone C, 0.848) and [a] f - -587 (acetone C, 0.921). Analyses and infrared spectra of individual enantiomers were identical to those of the racemic mixture. 

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