Isomerieverschiebung und Quadrupolaufspaltung beim Mößbauer-Effekt von Fe⁵⁷ in Eisenverbindungen

Abstract

Data from previous measurements are discussed from the point of view of isomeric shift and quadrupole splitting. For a comparison of isomeric shifts the magnitude of temperature shifts have to be regarded. Information about electric field gradients arises from the magnitude and the temperature dependence of quadrupole splittings. After putting the data into a suitable form, characteristic regions of the value of line shift, quadrupole splitting and temperature dependence of the splitting for different bond types are obtained. Besides this, influences of the crystal field are to be considered. Different types of contributions to the electric field gradient are discussed. The main features of field gradients in iron ions and molecules with and without closed electron shells are derived and compared with the experimental results. The result that the isomeric shifts for covalent bond iron in the oxydation states 0, +2, +3 and metallic bond iron are distributed over the same region whilst the ions Fe²⁺, Fe³⁺ and [Fe^VIO₄]²⁻ each have characteristic values is discussed.π-bonds in addition to σ-bonds and partially ionic bonds have to be considered. Based on the foregoing discussion the connection between the strength ofπ-bonds and the value of isomeric shifts and quadrupole-splittings and the sign of field gradients is regarded for iron ions and molecules, where ligands have been exchanged. Finally examples for the interdependence of the structure of multicenter-molecules and -ions and the data are given.