Nephelauxetic effect

The nephelauxetic effect is a term from the coordination chemistry of transition metals. It refers to the observation that the Racah parameter B decreases as a free ion of a transition metal forms a bond with ligands.

Removal of the Racah parameter indicates that the repulsion of two electrons in a doubly occupied d orbital is lower than in the corresponding gaseous metal ion, suggesting that the atomic orbital in the complex is greater than the ion. Possible explanations for this effect are expanding electron clouds:

• The effective charge of the metal is reduced by the influence of electron-withdrawing ligands, thus the d- orbitals can stretch more easily.

• Due to the overlap of the orbitals and the formation of a covalent bond, the orbital increased because of two atomic orbitals, a molecular orbital is formed.

Experimental studies show that the effect nephelauxetic following series follows:

The effect depends not only on the ligand, at constant ligand, the effect of the following series follows