Iron compounds, electric field gradient

Quadrupole splitting (A q) correlates to electric field gradient and, based on model compounds, can identify some ligand types Can observe changes in ligand field induced by sample perturbation Can only detect iron sites Magnetic circular dichroism (MCD) spectra Require low temperature to observe (—2-70 K)... 

What other measurements can be made which offer a comparison between model and biological compounds Iron is an element which can be studied by Mossbauer spectroscopy (Section 12.5.3). Mossbauer spectroscopy provides a way of determining whether, for instance, the electric field gradient at the iron is similar in model and biological species. The comparison is detailed in Table 16.2. Without going into a detailed discussion of the meaning of the quantities in this table (although Sections 12.5.2 and 12.5.3 provide an indication), it is evident that a reasonable accord exists and this conclusion is confirmed by a more detailed analysis—the iron atoms, indeed, are in similar environments. 

JJor chemists interested in modem theories of chemical bonding, the most useful data obtainable by the Mossbauer technique are the magnitude and sign of the electric quadrupole field gradient tensor and the magnitude of the shift, 8, (which we prefer to call the chemical isomeric. Cl, shift), of the center of the Mossbauer spectrum relative to some standard absorber. Although a considerable amount of chemical and structural information is potentially available from quadrupole data on iron compounds, relatively little use has been made of such data in the literature, and we will not discuss this parameter here. We will instead restrict ourselves to two main points review of the explanations put forth to explain Cl shift data in iron compounds, and a survey of some of the correlations and generalizations which have been found. 

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