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 when a free ion of a transition metal bonds with ligands.
The decrease in the Racah parameter indicates that the repulsion of two electrons in a doubly occupied d orbital is less than in the respective gaseous metal ion, which suggests that the atomic orbital in the complex is larger than in the ion. Possible explanations for this electron cloud expanding effect are:
- The effective charge of the metal is reduced by the influence of the electron-withdrawing ligands, which makes it easier for the d orbitals to expand.
- Overlapping the orbitals and forming a covalent bond increases the size of the orbital, since a molecular orbital was formed from two atomic orbitals. The particle in the box (TiK) model illustrates the energy gain of the electron in the larger system.
Experimental studies show that the nephelauxetic effect follows the following sequence:
The effect does not only depend on the ligand, if the ligand remains the same, the effect follows the following series
- Mn (II) <Ni (II) ≈ Co (II) <Mo (II) <Re (IV) <Fe (III) <Ir (III) <Co (III) <Mn (IV)
See also
Source
Housecroft CE and Sharpe AG, Inorganic Chemistry , 2nd Updated Edition, Pearson Study, 2006.
