Optical electronegativities of 3d group central ions

The optical electronegativity x opt behaves in essentially the same way in the 3d group as in the 4d and 5d hexahalides though the variation differs in details. Thus, the tetrahedral complexes have considerably higher x opt than the corresponding octahedral compounds. The slope of x opt versus the number q of electrons in the partly filled shell is compared for the 3d and 4f groups, and is smaller than in the gaseous ions as are also the differences of x opt between the oxidation numbers +3 and +2 for the same q.