Helicate versus Mesocate in Quadruple-Stranded Lanthanide Cages: A Computational Insight

Area of Science:

• Supramolecular Chemistry
• Computational Chemistry
• Materials Science

Background:

• Metallo-supramolecular assemblies (MSAs) offer tunable properties for advanced applications.
• Predicting and controlling the isomeric structures (helicate, mesocate) of MSAs is essential for their functional exploitation.
• Computational tools are vital for understanding the factors governing MSA stability.

Purpose of the Study:

• To computationally investigate the factors influencing the relative stability of helicate and mesocate isomers in lanthanide-based quadruple-stranded MSAs.
• To provide insights into ligand design and guest inclusion for controlling MSA structure and stability.
• To establish guidelines for the rational synthesis of specific supramolecular isomers.

Main Methods:

• Quantum mechanical calculations were employed to model lanthanide-based MSAs ([Ln2L4]2-).
• Three calculation setups were used: vacuum, solvent, and solvent with dispersion correction.
• The study analyzed the impact of ligand rigidity, steric hindrance, guest presence, and guest dimension on isomer stability.

Main Results:

• All computational setups accurately predicted the most stable isomer.
• Inclusion of dispersion correction was crucial for reproducing accurate geometrical parameters.
• Ligand flexibility and steric bulk significantly influence helicate vs. mesocate stability.
• Guest inclusion can invert isomer stability, particularly with flexible ligands and increasing guest size.

Conclusions:

• Computational modeling provides a robust approach to understanding and predicting MSA isomerism.
• Ligand design (rigidity, bulk) and guest properties (size) are key parameters for controlling helicate/mesocate ratios.
• These findings offer general guidelines for the targeted synthesis of functional lanthanide-based MSAs.