Inert Pair Effect - Failure of The Theory

Failure of The Theory

Part of the rationale for describing this as an effect was the fact that, at the time when it was proposed, there were no known compounds of Group 13 elements with the intermediate, +2, oxidation state. This is no longer true since the discovery of complexes of Ga(II) and In(II), such as the halo complexes 2-. These complex ions are stabilized by the formation of a covalent M–M bond. It follows that the instability of simple complexes of ions such as Ga2+ is due to kinetic factors, namely, that the Ga2+, having an unpaired electron, behaves as a free radical and is rapidly destroyed by reaction with another free radical. Drago was right, these compounds are thermodynamically stable by virtue of the formation of a covalent bond between the gallium ions.