Lanthanide(III) Complexes Based on an 18-Membered Macrocycle Containing Acetamide Pendants. Structural...

Area of Science:

• Coordination Chemistry
• Lanthanide Chemistry
• Supramolecular Chemistry

Background:

• Macrocyclic ligands are crucial for stabilizing lanthanide ions.
• Lanthanide coordination chemistry is sensitive to ligand structure and metal ion size.
• Functionalized macrocycles offer tunable properties for various applications.

Purpose of the Study:

• To investigate the coordination behavior of lanthanide complexes with a specific tetraazadipyridinacyclotetradecaphane scaffold.
• To elucidate the structural changes and solution properties across the lanthanide series.
• To evaluate the potential of these complexes as contrast agents.

Main Methods:

• X-ray crystallography to determine solid-state structures.
• Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy to study solution behavior.
• Paramagnetic Chemical Exchange Saturation Transfer (paraCEST) analysis to assess contrast agent potential.

Main Results:

• Lanthanide complexes exhibit varying coordination numbers (9-12) depending on metal ion size.
• A structural transition from 10- to 9-coordinate species occurs with decreasing lanthanide ion size.
• Lanthanide complexes show tunable magnetic properties and significant paraCEST effects for Pr³⁺ and Tb³⁺.

Conclusions:

• The macrocyclic scaffold accommodates different lanthanide ion sizes through adaptable coordination modes.
• Solution NMR and structural data confirm a size-dependent coordination change.
• The observed paraCEST effects highlight the potential of these lanthanide complexes in magnetic resonance imaging (MRI).