Correlations between molecular structure and charge distribution in organometallic complexes of lanthanoids and actinoids

The correlation between molecular structure and charge distribution was investigated in organometallic compounds of the lanthanoid (4f-) and actinoid (5f-) elements. These compounds are suitable models for two reasons: a) they are soluble in nonpolar solvents and b) in both series, there is a possibility for continuous variation of the ionic size of the central ion. Detailed investigation of several compound-classes with different molecular symmetry, has given important information concerning the influence of the molecular structure on the macroscopic charge distribution in the molecule. The anisotropy of the charge distribution in the molecule increases with decreasing of the molecular symmetry. Contrary to predictions previously discussed in the literature, it has been shown, that the molecular symmetry primarily does not depend on sterical interactions, but on the Coulomb-interaction between the central ion and the ligand. Using different models which take into account the molecular geometry and the charge distribution, it was possible to calculate the partial electrical moments between ligand and central ion for several coordinating atoms of the used ligands. The contribution of the f-electrons to the total charge distribution around the central ion can be quantitatively calculated from the molecular polarizability and the total charge distribution of the investigated molecule. (orig./RB)