Theoretical Insights into the Nature of Divalent Lanthanide-Ligand Interactions

The nature of the metal-ligand interaction in divalent samarium complexes is investigated by a variety of quantum chemical tools and compared to the analogous strontium-ligand interaction. The complexes under study are the decamethylsamarocene Sm(C5Me5)(2) the octamethyldiphosphasamarocene Sm(C4Me4P)(2), and the decamethylstrontocene Sr(C5Me5)(2). Molecular orbital descriptions, binding energy decompositions and topological analyses based on the electron density reveal the non-negligible role of covalency in the samarium-ligand interaction. The results are supported by an orbital energetic contribution in the metal-ligand interaction and a number of samarium-carbon bond critical points and electron localization function valence basins. The covalent contribution to the samarium-ligand bond contrasts with the highly ionic strontium-ligand interaction.