Helical lanthanide(III) complexes with chiral nonaaza macrocycle

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Lanthanide Chemistry

Background:

• Chiral macrocyclic ligands are crucial for creating enantiopure metal complexes.
• Lanthanide(III) ions offer unique electronic and magnetic properties for complex formation.
• Understanding stereoselectivity in macrocyclic complexation is key for developing chiral materials.

Purpose of the Study:

• To synthesize and characterize enantiopure helical complexes of various lanthanide(III) ions with a chiral nonaazamacrocyclic amine (L).
• To investigate the stereochemical preferences and solution behavior of these complexes.
• To explore the photophysical properties of selected lanthanide complexes for potential applications.

Main Methods:

• Synthesis of the chiral nonaazamacrocyclic amine L and its lanthanide(III) complexes.
• Characterization using spectroscopic methods (NMR, CD) and X-ray crystallography.
• Photophysical measurements including luminescence and circularly polarized luminescence (CPL).

Main Results:

• Enantiopure helical complexes of Ce(III), Pr(III), Nd(III), Eu(III), Gd(III), Tb(III), Er(III), Yb(III), and Lu(III) with L were successfully synthesized.
• X-ray structures revealed distinct thermodynamic helical preferences ((M) for early Ln, (P) for late Ln).
• NMR and CD studies indicated kinetic preference for (M)-helicity, with slow helicity inversion observed for late lanthanides in solution.
• Photophysical studies showed efficient energy transfer for Eu(III) and Tb(III) but low quantum yields, despite stable chiral emitting species confirmed by CPL.

Conclusions:

• The chiral macrocycle L effectively induces enantiopure helical structures in lanthanide(III) complexes.
• A clear distinction in thermodynamic helical preferences exists between early and late lanthanide ions.
• Late lanthanide complexes exhibit dynamic helicity inversion in solution, highlighting complex stereochemical behavior.
• While energy transfer is efficient, luminescence properties are limited by factors like intersystem crossing and non-radiative decay.