Radii of Transition Ions in Crystal Fields

The radii of divalent and trivalent iron-group ions, unlike those of ions with spherically symmetrical ground states, do not vary regularly with atomic number. This is interpreted as an environmental effect, resulting from crystal field splitting of the lower energy levels. An approximate calculation of the crystal-field radius contraction has been made for the hexaquo complexes present in crystalline hydrates and in aqueous solutions of the divalent ions. When this is subtracted from the observed radii, the resulting ``corrected'' quantities exhibit the smooth variation with atomic number expected for free ions.