The Lanthanide Contraction Is a Variable

Area of Science:

• Inorganic Chemistry
• Lanthanide Chemistry
• Coordination Chemistry

Background:

• Lanthanide contraction is a well-established phenomenon in inorganic chemistry.
• The extent of lanthanide contraction can be influenced by the coordination environment and ligand properties.
• Previous studies have not fully elucidated the varying degrees of lanthanide contraction across different ligand types.

Purpose of the Study:

• To investigate the variability of lanthanide (Ln) contraction in [Ln(SST)3(THF)2] and related complexes.
• To compare the Ln-contraction behavior with different ligand types, including tris(trimethylsilyl)siloxide (SST) and tetrahydrofuran (THF).
• To understand the underlying electronic and bonding factors contributing to the observed differences in Ln-contraction.

Main Methods:

• Analysis of crystallographic data for lanthanide complexes from the Cambridge Structural Database (CSD).
• Comparison of bond distances (Ln-O(THF) and Ln-O(SST)) across the lanthanide series (La to Lu).
• Gas-phase electronic structure calculations using density functional theory (DFT).

Main Results:

• A significantly larger variation in Ln-O(THF) bond distances (0.257 Å) compared to Ln-O(SST) (0.164 Å) was observed across the lanthanide series.
• This enhanced Ln-contraction for THF was found to be pervasive across similar structures and also observed with pyridine ligands.
• DFT calculations confirmed the experimental findings, attributing the variable Ln-contraction to differences in bonding types: ion-ion for Ln-SST and ion-dipole for Ln-THF.

Conclusions:

• The type of bonding interaction between the lanthanide ion and the ligand is a critical factor determining the extent of lanthanide contraction.
• Ion-dipole interactions (e.g., with THF) lead to a more pronounced lanthanide contraction compared to ion-ion interactions (e.g., with SST).
• This study provides a deeper understanding of the factors governing lanthanide contraction, essential for predicting and designing lanthanide-based materials.