Hexanuclear Ln₆ L₆ Complex Formation by Using an Unsymmetric Ligand

Area of Science:

• Supramolecular Chemistry
• Lanthanide Coordination Chemistry
• Materials Science

Background:

• Multinuclear lanthanide complexes offer potential as sensors and imaging agents.
• Synthetic and characterization challenges hinder systematic studies of lanthanide complex self-assembly.
• Lanthanide complex architectures are less diverse than those of transition metal counterparts.

Purpose of the Study:

• To investigate the effect of ligand backbone symmetry on multinuclear lanthanide complex self-assembly.
• To explore the formation of novel lanthanide architectures.
• To understand the critical factors influencing self-assembly.

Main Methods:

• Synthesis of homoditopic ligands with varying backbone symmetry.
• Formation and characterization of lanthanide complexes using mass spectrometry, luminescence, DOSY NMR, and EPR spectroscopy.
• Evaluation of counterion and lanthanide ionic radius effects.

Main Results:

• Replacement of a symmetric linker with an unsymmetric amide promotes the formation of an unusual Ln₆L₆ complex.
• Triflate counterions and specific lanthanide ionic radii are critical for Ln₆L₆ formation.
• Luminescence studies reveal differences between Eu₆L₆ and Eu₂L₃ complexes, with Eu₆L₆ showing signs of non-radiative decay.
• Homo-RIDME EPR experiments provided distance measurements in the Gd₆L₆ analogue.

Conclusions:

• Ligand backbone symmetry is a key determinant in controlling multinuclear lanthanide complex self-assembly.
• The identified Ln₆L₆ architecture presents coordinatively unsaturated metal centers, offering unique properties.
• This work provides insights into the rational design of novel lanthanide-based supramolecular structures for advanced applications.