“Ionic radii,” spin-orbit coupling and the geometrical stability of inorganic complexes

The van Santen and van Wieringen theory of “ionic radii” is briefly reviewed and extended to include spin-orbit influences. It is noted that, although for the most part spin-orbit forces have little effect upon stereochemical predictions made for the first transition series, noteworthy exceptions to this rule occur for octahedral complexes of Co
⁺⁺
and tetrahedral complexes of Ni
⁺⁺
and Cu
⁺⁺
. Indeed, it is found that spin-orbit coercions render the ground states of these molecules Jahn-Teller resistant. Diagrams are displayed and tables compiled to illustrate the variation of ionic radii with atomic number for the second and third transition series. Paths for future theoretical research are indicated and an exhortation for closer theoretical-experimental alliance is promulged.