Two [Ln₄] molecular rings folded as compact tetrahedra

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Photoactive ligands offer potential for creating multifunctional molecular nanomagnets.
• Developing novel ligands with switchable properties is crucial for advanced magnetic materials.

Purpose of the Study:

• To design and synthesize a new multitopic chelating ligand with a photoswitchable unit.
• To investigate the formation and properties of supramolecular assemblies incorporating this ligand with lanthanide ions.
• To explore the magnetic properties, specifically magnetization relaxation, of the resulting dysprosium-based nanomagnet.

Main Methods:

• Synthesis of the multitopic chelating ligand 1,2-bis-(5-(N'-(pyridine-2-yl-methylene)-carbohydrazide)-3-methyl-thien-3-yl)-cyclopentene (H2L).
• Reaction of H2L with LnCl3 salts (Ln = Dy, Tb) in the presence of NaH to form supramolecular assemblies.
• Single crystal X-ray diffraction analysis to determine the structures of the molecular rings.
• Magnetization relaxation measurements to study the magnetic behavior of the dysprosium analog.

Main Results:

• The ligand H2L undergoes reversible photoisomerization in solution.
• Supramolecular assemblies [Ln4L4Cl4(H2O)4] (Ln = Dy, Tb) were formed, featuring highly symmetric molecular rings.
• The ligand's conformation within the rings inhibited its photoswitching activity.
• The dysprosium analog exhibited slow relaxation of magnetization, with mechanisms elucidated through varied condition studies.

Conclusions:

• A novel photoactive ligand was successfully synthesized and incorporated into lanthanide-based supramolecular structures.
• The structural arrangement within the molecular rings influenced the ligand's photochromic behavior.
• The dysprosium-containing nanomagnet displays promising slow magnetic relaxation properties, relevant for molecular magnetism applications.