Valency and spin

By far the most utilized Mossbauer isotope is Fe, particularly in (bio)inorganic chemistry. Most iron compounds are found in the oxidation states iron(ll) and iron (III), either with low-spin or high-spin electron configuration. The literature on the application of Fe Mossbauer spectroscopy in this field of research has been reviewed in several textbooks, which are referenced in Chap. 1. The present chapter is intended as a survey of the Mossbauer studies on iron compounds with less common, nevertheless increasingly interesting, valence and spin states. 

Figure 2. Range of Cl shifts in iron compounds characteristic of various valencies and spin states. Question marks at the ends of the lines indicate the extreme limits have not been well defined...

Includes 5s5p core-valence and spin-orbit corrections These values were cited in Ref (13). 

The electric monopole interaction is a function of the s electron densities at the nucleus. This results in a displacement of the spectrum and is expressed as the velocity of the source (mm s ) necessary to counteract the displacement. This isomer (or chemical) shift, 6, provides information about the coordination number, the valency and spin state of the iron in the compound. 

The valence and coordination symmetry of a transition metal ion in a crystal structure govern the relative energies and energy separations of its 3d orbitals and, hence, influence the positions of absorption bands in a crystal field spectrum. The intensities of the absorption bands depend on the valences and spin states of each cation, the centrosymmetric properties of the coordination sites, the covalency of cation-anion bonds, and next-nearest-neighbour interactions with adjacent cations. These factors may produce characteristic spectra for most transition metal ions, particularly when the cation occurs alone in a simple oxide structure. Conversely, it is sometimes possible to identify the valence of a transition metal ion and the symmetry of its coordination site from the absorption spectrum of a mineral. 

The electric field has now been taken in the x-direction, and the polarization is assumed to be parallel to the field. For cubic crystals the susceptibility is independent of field direction. The k values are to be summed over all valence and spin states, and the k values over all conduction-band states of the same spin. 

The quadrupole splitting depends on the valence and spin state of the absorber atoms, as well as the coordination and degree of distortion of the crystallographic site. Values of AEq extend from zero to a maximum of approximately 3.7... 

By using the optical basicity Ath of cations in their appropriate coordination, valence, and spin, it is possible to calculate the theoretical optical basicity of mixed oxides, oxysalts, or of any oxygen-containing sohd, if the stoichiometry is known. Given a M oxide or mixture, Au, is calculated by the linear combination of stoichiometry x,, valence and A, of the / cations (n = oxygen stoichiometry), according to ... 

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