Electronic charge and spin distribution in some iron halides from the interpretation of theFe57andI129hyperfine interactions

The ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ isomer shifts in the ${\mathrm{Fe}}^{2+}$ and the ${\mathrm{Fe}}^{3+}$ halides are interpreted from electron-density calculations at the nucleus to provide the proportionality constant between these two quantities: $\alpha =-0.20\mathrm{}{a}_0^3$ mm/sec. In the tetrahedral ${\mathrm{Fe}}^{3+}$ halides the magnetic hyperfine fields are also computed at the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nucleus from semiempirical molecular-orbital calculations. In the ${\left(\mathrm{F}\mathrm{e}{\mathrm{I}}_4\right)}^{-}$ complex the intramolecular electron charge and spin rearrangement is discussed self-consistently for both the iron and the iodine atoms on the basis of the semiempirical valence-bond theory and of molecular-orbital cluster calculations.