Iron complexes, high-spin

The facility with which Fe 14-41-keV MSssbauer spectra can be measured has resulted in considerable use of the technique for probing iron solid-state systems so much so that it would be impossible to summarise the data adequately in a single chapter. The general field of iron chemistry has therefore been subdivided into a number of subsections and, although this division is to some extent arbitrary it simplifies the task of presenting the results considerably. The subsections are as follows, 

The present chapter will be restricted to the first of these subjects. Since high-spin ferrous (Fe +) and ferric (Fe +) cations have somewhat different orbital properties, as outlined in Chapter 5, we shall consider each in turn. Many complexes have been examined by several workers in the past few years, and the data currently available for each will be presented. Early references which do not contribute significant information beyond that given in the later papers will be omitted where appropriate, but references to such papers will in many cases be found in the papers cited. 

Great difficulty has been found in comparing chemical isomer shifts from different laboratories. Comparatively large discrepancies have frequently been found, and it has been necessary to restrict comment to examples where differences in chemical isomer shift can confidently be held to be significant. 

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At the present time we have no certain knowledge of the state of the heme in these 450 nm species. We do not know if there are heme aggregates although they are unlikely. It is therefore reasonable to look at systems where the haem is aggregated as well as those where it is not in order to see how the absorption spectra can be mimic-ed. It seems reasonable to assume that the iron is low-spin in the carbon monoxide, isocyanide, and nitric oxide complexes as no high-spin iron complexes of this type are known. In the high-spin or low-spin state it may be that the thiol is weakly bound, if at all, for Fe(II) heme in models or in hemoglobin does not bind to thiols. In an attempt to understand these spectra we shall use a semi-empirical approach based on the theoretical discussion in the previous article (52) and elaborated in what follows immediately. Only Fe(II) complexes will be analysed as the Fe(III) proteins have been previously examined (52). 

The Fe Mdssbauer parameters for the clathrochelate [FeMn(trom)](BF4) and [Fe2(trom)](BF4) complexes are characteristic of high-spin iron complexes. The spectrum of the [FeMn(trom)](BF4) clathrochelate exhibits one doublet line, which indicates the sole type of coordination centre. The QS value increases regularly with a temperature decrease. A major contribution to the QS value is made by the valence component (the lattice component is small and practically independent of temperature). For [FeMn(trom)](BF4) clathrochelate, all three spin-quintet states are presumably within kT, and the QS value depends on temperature [192]. 

HIGH-SPIN IRON COMPLEXES Iron(UI) Alums and Jarosites... 

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