Macrocyclic Ligands with an Unprecedented Size-Selectivity Pattern for the Lanthanide Ions.

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Lanthanide ions (Ln³⁺) are crucial in various applications, typically as coordination compounds.
• Achieving selective binding of specific lanthanide ions is challenging due to their similar chemical properties.

Purpose of the Study:

• To design and synthesize novel macrocyclic ligands with dual selectivity for lanthanide ions.
• To investigate the structural and thermodynamic properties of lanthanide complexes formed with these new ligands.

Main Methods:

• Potentiometric titrations to determine thermodynamic stability and selectivity.
• Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray crystallography for structural analysis.
• Density Functional Theory (DFT) calculations to elucidate the origin of selectivity.

Main Results:

• Two 18-membered macrocyclic ligands, macrodipa and macrotripa, were synthesized.
• These ligands exhibit unprecedented dual selectivity, binding both light, large Ln³⁺ and heavy, small Ln³⁺ ions.
• Structural studies revealed a conformational toggle (10-coordinate Conformation A to 8-coordinate Conformation B) accommodating different ion sizes.

Conclusions:

• Novel ligand design can effectively tune lanthanide ion selectivity.
• The observed dual selectivity arises from a balance between ligand strain and metal-ligand binding energies.
• This work provides a new platform for developing selective lanthanide separation and application technologies.